HCCHILLSBOROUGH COMMUNITY COLLEGE

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Dr. Drew H. Wolfe

 
CHEMISTRY--THE STUDY OF MATTER AND ENERGY
 
Section | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | Bottom Return to WWWolfe |
 
 
 1.1 INTRODUCTION TO CHEMISTRY

What is Chemistry?

Chemistry is one of the most exciting and relevant areas of study because almost all aspects of life are to some degree related to chemistry. Chemistry is the science that is concerned with the composition of matter and the changes that matter undergoes.

What is a Chemist?

A chemist is a person who studies the composition, structure, and properties of matter and seeks to explain the changes that matter undergoes.

Matter and Energy

What is matter? It includes anything that has mass and occupies space. The earth, and everything on it, is composed of matter. The terms substances, materials, objects, and bodies are used to refer to matter. Examples of matter are as far ranging as the air you breath, the food you eat, the objects that you own, and the ground upon which you walk. Matter is closely associated with energy, and in some rare instances cannot be easily distinguished from energy. Energy is the ability to do work.

Chemistry and the Other Sciences

Chemistry overlaps with and is an integral part of the other sciences. Biology, the study of living systems, applies chemical principles to help understand cells, the basic units of life. Geology, the study of the earth, incorporates chemical observations to understand the processes that occur on earth.

Physics and chemistry, both physical sciences, overlap to a large degree because physics also deals with matter, energy, and the interaction of the two. The principal difference between physics and chemistry is that physicists are more interested in the most fundamental components and regularities of nature and how they fit together to yield our universe. Chemists and physicists make use of the same laws of nature to gain a better understanding of the properties and behavior of matter.

Divisions of Chemistry

The study of chemistry may be separated into artificial divisions that categorize the most significant areas of study. These overlapping divisions include: analytical, inorganic, organic, biological, physical, and geological chemistry. An insight into each division is gained by considering what the various types of chemists study.

Analytical Chemists

Analytical chemists study the identities and amounts of the components of matter. Most chemists use analytical procedures and techniques to some degree in their studies.

Inorganic and Organic Chemists

Inorganic chemists study the properties, structures, and reactions of all elementary substances. One of these substances, carbon, has a special set of properties. Therefore, a division of chemistry is entirely devoted to this vast topic. It is called organic chemistry. Organic chemists investigate the properties of carbon compounds and how they react.

Biological Chemists

Biological chemists, also called biochemists, study the compounds that compose living things which include proteins, carbohydrates, proteins, lipids, and nucleic acids. They also study how these compounds interact to produce living systems.

Physical and Geochemists

Physical chemists apply the concepts of physics and develop theories to better understand the behavior of matter and its interaction with energy. Geochemists investigate the structures, properties, and reactions of substances found in the earth's crust, atmosphere, and oceans.



Problem 1.1

What type of chemist would study each the following? (a) rocks and minerals, (b) synthesis of a new carbon compound, (c) effect of antibiotics, (d) structure of metals

Solution 1.1

(a) geochemists, (b) organic chemists, (c) biochemists, (d) inorganic chemists



 Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

1.2 PROPERTIES OF MATTER

What is matter?

Matter is anything that has mass and occupies space. One of the principal concerns of chemists is to study the composition and structure of matter. Composition refers to the identity and quantity of the components (ingredients) of matter. The structure of matter refers to the physical arrangement of the components within matter. Collectively, the composition and structure determine the properties, or characteristic traits, of matter.

What are the Properties of Matter?

Each type of matter has its own unique set of properties. Thus, different types of matter are distinguished by their properties, as people are distinguished by their physical appearance and personality traits.

Physical Properties

Physical properties are characteristics of an individual substance that can be determined without changing the composition of the substance. Substances are the most basic forms of matter: elements and compounds. Some examples of physical properties are color, hardness, electrical conductivity, heat conductivity, physical state, melting point, and boiling point. Physical properties are measured by observing what happens when matter interacts with heat, light, electricity, and other forms of energy, or when matter is subjected to various stresses and forces.

Each substance has a unique set of physical properties that distinguishes it from all other substances. If two substances have exactly the same set of physical properties, the most plausible conclusion is they are the same substance with the same composition and structure.



Problem 1.2

(a) List three physical properties of water. (b) List physical properties of gold.

Solution 1.2

(a) Water is a liquid that boils at 100oC and freezes at 0oC.

(b) Gold is a bright-yellow solid that boils at 2808oC and melts at 1063oC. It is a malleable metal (can be hammered into different shapes) with a high density (ratio of mass to volume).



 

Physical Changes

A physical change occurs when the physical properties of a substance are altered, but the composition remains the same. No new substance forms in a physical change. Examples of physical changes are changes in state, density, shape, magnetic properties, and conductivity. After a physical change, the starting substance is still present but in a modified state.



Problem 1.3

Explain why each of the following is a physical change. (a) a rock is crushed and a powder results, (b) ice melts, (c) iron is magnetized

Solution 1.3

(a) Both the rock and powder have the same composition. Only the particle size has changed.

(b) When ice melts, water changes from the solid state to the liquid state.

(c) Both unmagnetized and magnetized iron are both iron; hence, they have the same composition.



 

Chemical Properties

Chemical properties describe how the composition of a substance changes or does not change when it interacts with other substances or energy forms. Terms used to describe chemical properties are "reactive," "inert," "unstable," and "combustible." Chemical properties are observed when a substance changes composition. Some examples of chemical properties include: paper burns in air; iron rusts; silver tarnishes; and TNT explodes. In each of these examples, a new substance forms after the chemical change.

Chemical Changes

Chemical changes, also called chemical reactions, are the result of the chemical properties of matter. After a chemical change, the composition is no longer the same.

Chemical Changes and Chemical Equations

For each chemical change, a chemical equation can be written that shows what the original substance, or substances, are ultimately changed to. The starting materials, called reactants, undergo a chemical change and produce the products.

Reactants ---> Products

The arrow that separates the reactants from the products is a symbol that means "yield" or "produce." In chemical reactions, the reactants combine to yield the products.

Examples of Chemical Changes

Chemical changes are monitored by first observing the physical properties of the reactants, and then considering the physical properties of the products. If a chemical change has truly taken place, some or all the physical properties of the products are different from those of the reactants. Examples of everyday chemical changes include rusting iron, cooking foods, ignition of gasoline, explosion of dynamite, and burning wood.



Problem 1.4

Classify each as a physical or chemical property. (a) When limestone is heated carbon dioxide and calcium oxide result. (b) Ice floats on water. (c) Copper can be drawn into thin wires. (d) Milk sours if not refrigerated. Explain each answer.

Solution 1.4

(a) Chemical property. Because two new substances are formed after heating, this is a chemical property. If a physical change had occurred, limestone would have been present after heating.

(b) Physical property. Floating involves no change in physical properties, which immediately eliminates the possibility of a chemical change. Ice floats on water because ice has a lower density than liquid water.

(c) Physical property. The shape of copper is changed when drawn into wires. Its composition does not change.

(d) Chemical property. A change in the taste of the milk shows that one or more new substances is present in the sour milk that was not present in the fresh milk. The increase in the concentration of acid produced from microorganisms causes milk to sour.




Problem 1.5

Classify each of the following as a physical or chemical change. (a) Liquid water evaporates to produce water vapor. (b) Fermenting grapes produce ethanol. (c) A candle burns. Explain each answer.

Solution 1.5

(a) Physical change. When water evaporates the composition remains constant. Water is present in two different states; thus, a physical change has occurred.

(b) Chemical change. Fermentation is the process in which yeast is added to crushed fruits or grains to produce ethanol, the drinking variety. Ethanol, a new substance, is formed after fermentation, indicating a chemical change.

(c) Chemical change. Whenever a substance is burned the initial substance, a candle in this example, is changed to new substances with new compositions; accordingly, the change is chemical.



Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

1.3 STATES OF MATTER

All matter on earth exists in three physical states: solids, liquids, and gases. The properties most often used to distinguish the three states of matter are shape, volume, average density, structure, viscosity (resistance to flow), and compressibility. The physical state of a substance depends on its temperature and pressure. Unless otherwise noted, room conditions of 25oC (298 K) and normal atmospheric pressure (1 atm, a unit of gas pressure) are assumed.

Solids

Solids have fixed shapes that are independent of their containers. The volume of a solid is constant and does not change when a pressure is exerted. Solids are almost completely incompressible. Of the three states of matter, solids have the highest average density (ratio of mass to volume). Densities greater than 1 g/cm3 are the norm for solids. A high average density means that the particles that compose solids are usually packed closer than those in liquids or gases. The tightly packed particles of solids are also highly organized. Solids have practically no ability to flow because the particles that compose a solid are very tightly bonded. This means that solids have very high viscosities.

Liquids

Liquids are different from solids in many respects, but they share some common characteristics. Like solids, liquids are essentially incompressible. This means that pressure exerted on liquids generally produces little, if any, change in their volumes. When placed into a container, liquids assume the shape of the bottom of the container to the level they fill. The average density of liquids is less than that of solids but greater than that of gases. Liquid particles are not bonded as strongly as those in solids, and they are less orderly--more randomly distributed. Both of these factors tend to increase the average volume of liquids relative to solids. Viscosities of liquids vary over a broad range. Because liquids have much lower viscosities than solids, they are significantly more fluid than solids. However, the viscosities of liquids are higher than those of gases.

Gases

Gases bear little resemblance to the more condensed states of matter--solids and liquids. To a degree, the properties of gases are the opposite of those of solids. Gases completely fill the volume of their containers; are compressible; have a completely disorganized structure; possess the lowest average density; and have the lowest viscosities.



Problem 1.6

What physical states best fits the following descriptions? (a) highly organized structure and high viscosity, (b) no organized structure and low viscosity, (c) relatively high densities and have a range of viscosities

Solution 1.6

(a) Solid, (b) gas, (c) liquid


Changes of State--Melting and Freezing

Matter can change from one physical state to another. For example, solids, when heated, change to liquids. The characteristic temperature at which a solid changes to a liquid is called the melting point. At the melting point, both the solid and liquid states of the substance coexist. Liquids, in turn, change to solids as they are cooled. The temperature at which a liquid becomes a solid is called the freezing point. Freezing and melting occur at the same temperature.

Changes of State--Boiling and Condensing

Liquids when heated change to their vapors. A vapor is the gaseous phase of a substance. The transition temperature for this change is termed the boiling point. At the boiling point both the liquid and vapor states coexist. When a substance boils, vapor bubbles can be seen throughout the liquid phase. In the opposite direction, from vapor to liquid, the change is called condensation.

Change of State--Subliming

Numerous solids change directly to their vapors without going through the liquid state. This state change is called sublimation. At the temperature and pressure that a substance sublimes the solid and vapor states coexist.



Problem 1.7

What physical states coexist at the following transition points? (a) melting point, (b) subliming point, (c) freezing point, (d) boiling point?

Solution 1.7

(a) solid, liquid, (b) solid, vapor, (c) solid, liquid, (d) liquid, vapor



 Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

1.4 CLASSIFICATION OF MATTER

Matter exits in many different forms throughout the earth. Every year, thousands of new types of matter are synthesized. When dealing with such a large variety of substances, it is best to divide this enormous group into smaller categories with similar types of matter. Matter may be divided into two major groups--pure substances and mixtures.

Pure Substances 

A substance is classified as pure if it meets the following three criteria: has the same composition throughout the sample; its components are inseparable using physical methods; and changes of state occur at a constant temperature.

Pure substances are subdivided into two groups, elements and compounds. Elements are pure substances that cannot be decomposed by chemical changes. Compounds are pure substances that may be chemically decomposed to elements.

Elements

Elements are the basic units of matter. Today, approximately 110 different elements are known. About 92 elements occur in nature, and the remaining are synthetic. At 25oC, 97 elements are solids, 2 are liquids and 11 are gases.

Elements and the Periodic Table

All of the elements are listed, using their symbols, in the periodic table. Each element is located in a horizontal row called a period, and in a vertical column called a group (sometimes called a family). Each period is numbered consecutively from 1 to 7. Two numbering systems are used to designate the groups. One method uses a Roman numeral and either the letter A or B. The second method numbers the groups consecutively from 1 to 18.

Chemical Symbols of Elements

Chemical symbols are used to represent elements. Many chemical symbols are usually derived from the first one or two letters of the English or old Latin name of the element. For those with two letters, the first letter is always an uppercase letter, and the second is a lowercase letter. Some of these symbols are the first two letters of the English name, others are the first two letters of an old name, and the remainder contain the first letter plus some other letter in the name.



Problem 1.8

What are the symbols for the following elements? (a) boron, (b) aluminum, (c) sodium, (d) copper, (e) cobalt, (f) beryllium

Solution 1.8

(a) B, (b) Al, (c) Na, (d) Cu, (e) Co, (f) Be
 



 

Problem 1.9

What are the symbols for the following elements? (a) magnesium, (b) manganese, (c) potassium, (d) chlorine, (e) silver, (f) lead

Solution 1.9

(a) Mg, (b) Mn, (c) K, (d) Cl, (e) Ag, (f) Pb


 

Problem 1.10

What are the names of the following elements? (a) C, (b) Sc, (c) Ni, (d) Br, (e) Ca, (f) F

Solution 1.10

(a) carbon, (b) scandium, (c) nickel, (d) bromine, (e) calcium, (f) fluorine


 


Problem 1.11

What are the names of the following elements? (a) Sn, (b) U, (c) Ba, (d) P, (e) S, (f) N

Solution 1.11

(a) tin, (b) uranium, (c) barium, (d) phosphorus, (e) sulfur, (f) nitrogen



Atoms

Atoms are the smallest particles that retain the chemical properties of elements. Atoms are extremely small; one gram of carbon, C, contains 5 x 1022C atoms. Each element is composed of similar atoms. Both the chemical and physical properties of an element are directly related to the composition and properties of its atoms.

Compounds

Compounds make up the other class of pure substances. They are more complex than elements. Elements undergo chemical reactions to form compounds; thus, compounds are chemical combinations of elements. Hence, compounds can only be separated into their component elements by chemical means. The smallest subdivision of a compound is a molecule (or formula unit), a chemical combination of atoms.

Chemical Formulas of Compounds

Formulas are used to represent compounds. Each formula shows the specific composition of a compound. For example, the chemical formula of water is H2O. What information is conveyed by the formula of water? It indicates that all water is composed of two parts hydrogen and one part oxygen. Additionally, the formula of a compound gives the ratio of atoms within one molecule of that compound. For example, water molecules are particles with two hydrogen atoms and one oxygen atom.

In each chemical formula, the symbols of the atoms are listed with a subscript--a number written to the right and below the symbol--which gives the number of atoms in the molecule. If only one atom of a given element is found in the molecule, the subscript of 1 is not written; it is understood to be 1. In the formula of the water molecule, H2O, the subscript 2 is placed next to H, but no subscript is written next to O because only one O atom is found per molecule.

In more complex formulas, parentheses are used to group repeating units. For example, the formula of calcium phosphate is Ca3(PO4)2. Calcium phosphate has two PO4 groups, phosphate, which is actually PO43- groups. Instead of writing PO4 twice, it is enclosed in parentheses with 2 as the subscript to the right. The formula for calcium phosphate shows three Ca atoms, two P atoms, and eight O atoms are in calcium phosphate.



Problem 1.12

The formula for the gas carbon dioxide is CO2. What does this indicate about the compound carbon dioxide and its molecules?

Solution 1.12

The formula states that carbon dioxide is composed of one part carbon and two parts oxygen, and its molecules have one carbon atom and two oxygen atoms.
 



 

Problem 1.13

Write the name and number of each atom in the following molecules? (a) N2O, (b) CH4, (c) C6H12O6, (d) P2O5

Solution 1.13

(a) two nitrogen atoms and one oxygen atom, (b) one carbon atom and four hydrogen atoms, (c) six carbon atoms, twelve hydrogen atoms, and six oxygen atoms, (d) two phosphorus atoms and five oxygen atoms


 

Problem 1.14

Write the name of each atom and tell how many atoms are in each of the following. (a) Fe(OH)3, (b) Ba(NO3)2, (c) (NH4)2C2O4

Solution 1.14

(a) one iron atom, three oxygen atoms, and three hydrogen atoms, (b) one barium atom, two nitrogen atoms, and six oxygen atoms, (c) two nitrogen atom, eight hydrogen atoms, two carbon atoms, and four oxygen atoms



Mixtures

Mixtures are the second major division of matter. They are more complex than pure substances because mixtures are composed of two or more pure substances that are physically associated. A mixture has a variable composition, its components may be separated by physical methods, and it changes state occur over a range of temperatures. Milk, gasoline, asphalt, ocean water, granite, and air are some examples of mixtures.

Homogeneous and Heterogeneous Mixtures

Mixtures are divided into two classes, homogeneous and heterogeneous mixtures. "Homogeneous" is a word derived from homo which means the "same" or "equal," and genus which means "kind" or "structure." "Hetero" is a prefix that means "different."

Heterogeneous Mixtures

A heterogeneous mixture is one that exhibits more than one phase. A phase is an observable region of matter with a different composition than the surrounding regions. Each phase can be distinguished from bordering regions by its properties. For example, when sand is added to water, the sand does not dissolve. It just falls to the bottom of the water. Oil and water, salt and sand, and granite are all examples of heterogeneous mixtures.

Homogeneous Mixtures--Solutions

Homogeneous mixtures are also called solutions. Only one phase is can be seen in homogeneous mixtures. For example, consider a sugar-water solution. It is prepared by mixing solid sugar and liquid water. After the sugar dissolves, a homogeneous mixture results. Other examples of homogeneous mixtures include alcohol and water, alloys (solutions of metals), and air.



Problem 1.15

How can a mixture of sand and salt be separated?

Solution 1.15

A combination of sand and salt is a heterogeneous mixture. One contrasting property of each, their abilities to dissolve in water, provides a convenient method of separation. Salt dissolves in water, whereas sand does not. Thus, the following steps can be used to separate them.

1. Add water and dissolve the salt. The sand is unaffected.

2. Filter the resulting salt water solution from the sand.

3. Evaporate the water to recover the salt.
 


Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

1.5 ENERGY

Energy is defined as the ability to do work. What does this mean? Work is done when matter is moved by applying a force--a push or pull. Lifting a book off a table or throwing a baseball requires work. In science, something must be moved to do work. Energy, therefore, is the capacity to move or effect changes in matter. Two general classes of energy exist, potential and kinetic energy.

Potential Energy

Potential energy is stored energy. This potential or stored energy results from the position, condition, or composition of a body. A boulder moved from the ground to the top of a cliff has potential energy of position with respect to the ground. The boulder can fall off the cliff and crush objects below. A compressed spring has potential energy of condition; spontaneously, the spring can expand and do work by pushing something. A vial of nitroglycerine possesses potential energy of composition or chemical potential energy.

Kinetic Energy

Kinetic energy is associated with matter in motion. Whenever an object is moving, it possesses kinetic energy. The following formula is used to calculate kinetic energy, Ekinetic, of an object.

Ekinetic = 1/2 mv2 (1.1)

In this formula m is its mass, and v is its velocity or speed. This equation shows that the kinetic energy of a body is proportional to its mass and its velocity squared. The more massive an object and the faster the object is moving, the greater the kinetic energy it possesses.

Types of Energy

Energy is encountered in many different forms. Some examples include mechanical energy, electric energy, nuclear energy, light, heat, and sound. These examples are forms of energy because each has the capacity to produce changes in matter.

Energy Conversions

Energy can be converted from one form to another. For example, a boulder on the top of a cliff has potential energy only. But as soon as it falls from the cliff, the potential energy of the boulder is changed to energy of motion, or kinetic energy. When the boulder hits the ground, it stops moving and therefore no longer possesses kinetic energy.


Problem 1.16

Explain the energy conversions in an automobile.

Solution 1.16

The energy released when gasoline is burned is transformed into mechanical energy. The chemical potential energy of the gasoline is released, causing a piston to move which is mechanically linked to the movement of the wheels of the automobile. Along with the mechanical energy, heat is also released, an unavoidable transformation.
 


Heat

Heat or thermal energy is especially important to chemists. Why? All other forms of energy can be transformed into heat. In addition, heat changes accompany chemical reactions. Heat is a form of kinetic energy. This means it can never be classified as potential energy. Heat brings about both chemical and physical changes. Solids melt, liquids evaporate, and some substances decompose or undergo chemical changes when heated.

Heat and Temperature

When heat is transferred to matter it increases the potential energy, or the kinetic energy, or both. What happens when a substance is heated? A substance becomes hotter because the heat transferred increases the average motion of the molecules--an average kinetic energy increase. The increase in kinetic energy is observed by measuring the temperature of the substance. Temperature is a measure of the average kinetic energy of atoms and molecules. On an average, pure substances at higher temperatures have faster moving molecules than those at lower temperatures.

Heat, Temperature, and Change of State

Heat transferred to ice at 0.0oC gives a different result. When ice is present, added heat does not increase its temperature. State changes of pure substances occur at a constant temperature. Added heat increases the potential energy of the molecules in the solid ice to the point when many of their bonds break, allowing these molecules to enter the liquid state. Only after the ice has melted totally does the temperature increase. This temperature rise indicates an increase in the average kinetic energy of the molecules.

Heat Transfer

Heat is detected only when it moves from one object to another. Heat always transfers spontaneously from a hotter object to a colder object. The reverse never occurs spontaneously. When two objects at different temperatures contact each other, heat transfers spontaneously from the hotter object to the colder object. Faster-moving molecules, within the hotter object, collide with the slower-moving molecules, in the colder object. During the molecular collisions energy is transferred, decreasing the average kinetic energy of the faster-moving molecules and increasing that of the slower-moving molecules. When their average energies are equal, heat flow stops (thermal equilibrium establishes).



Problem 1.17

Explain what happens to the temperature and heat when a cup of hot coffee is allowed to sit in a room.

Solution 1.17

As time passes, the temperature of the coffee drops. If the coffee is not consumed, its temperature continues to drop until it equals the temperature of the room. Heat flows from the coffee and heats the room. But, compared to the total amount of heat in the room, the small quantity of heat released by the coffee is insignificant.
 



 

Problem 1.18

Describe the heat flow and temperature changes when a hot metal at 100oC is placed into a container of water at 25oC.

Solution 1.18

The temperature of the hot metal decreases as heat flows from the metal to the water. The temperature of the water increases as it absorbs the heat from the metal. Ultimately, the temperature of the metal and water equalize and the heat flow stops.


Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe | 

1.6 CONSERVATION OF MATTER AND ENERGY

Laws of Conservation of Mass and Energy

The law of conservation of mass states that mass cannot be created or destroyed. Applied to chemical reactions, this means that the total mass of the reactants equals the total mass of products. The law of conservation of energy states that energy cannot be created or destroyed. Energy may be converted from one form to another. During these conversions no energy is lost.

Law of Conservation of Matter/Energy

The laws of conservation of mass and energy were merged by Albert Einstein who proposed that matter and energy are equivalent. He expressed this relationship in the following equation

E = mc2 (1.2)

in which E is the change in energy in J, m is the change in mass in kg, and c is the velocity of light, 3.00 x 108 m/s. Equation 1.2 states that matter and energy are interconvertible. A tiny amount of matter transforms into a huge amount of energy in nuclear bombs or nuclear power plants. For most chemical reactions, nonnuclear changes, the amount of matter converted to energy is too small to measure on a balance, and it is correct to say that both matter and energy are conserved.
  



Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

SUMMARY

The study of chemistry is concerned with the composition of matter and the changes that matter undergoes. Six major divisions of chemistry are analytical chemistry, inorganic chemistry, organic chemistry, physical chemistry, biochemistry, and geochemistry. Within science, chemistry is sometimes considered the central science because all other sciences, to a degree, deal with matter.

Our universe is composed entirely of matter and energy. Matter is anything that has mass and occupies space. Energy is the capacity to do work.

Physical properties are characteristics of individual substances that can be measured without changing the composition of a substance. Chemical properties describe how the composition of a substance changes when it interacts with other substances or energy forms.

Solids are the most dense and most viscous of the physical states. In contrast, gases are the least dense and least viscous. Solids have a fixed shape and volume; gases expand and take the shape of their containers, and have a variable volume. The structure of liquids more closely resemble that of solids than gases. Liquids have a relatively high average density and are incompressible.

Matter is divided into two general classes, pure substances and mixtures. Pure substances have a constant composition, cannot be separated by physical means, and undergo state changes at a constant temperature. Mixtures have a variable composition, can be separated using physical means, and undergo state changes over a wide temperature range.

Pure substances are subdivided into elements and compounds. Elements are the most fundamental units of matter. Compounds are produced when elements are chemically combined. Elements are composed of small particles called atoms, and compounds are made up of molecules, which are chemical combinations of atoms.

Mixtures can either be homogeneous or heterogeneous. A homogeneous mixture is a combination of pure substances that can be separated by physical means, has a variable composition, undergoes state changes over a temperature range, and exhibits only one phase. Homogeneous mixtures are called solutions. Heterogeneous mixtures differ from homogeneous mixtures in that they possess two or more phases.

Potential energy is stored energy, and results from the position, condition or chemical composition of an object. Kinetic energy is the energy of motion. All objects that move possess kinetic energy. The kinetic energy of an object is proportional to its mass and its velocity squared.

Energy can be interconverted from one form to another. Whenever energy is interconverted, some of the energy is usually lost as heat. Heat always flows from a hotter object to a cooler one.

Matter and energy are interconvertible--matter can be changed to energy or vice versa. However, in normal chemical changes, both matter and energy are conserved. The same quantity of matter is present, after a chemical reaction, as was originally present. Matter cannot be created or destroyed. Likewise, energy cannot be created or destroyed.
 



Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe | 

CHAPTER 1 REVIEW EXERCISE

1. Classify each as either a physical or chemical property: (a) existence in the solid state, (b) magnetic properties, (c) explosiveness, (d) combustibility, (e) flammability

2. Classify each of the following properties as physical or chemical. (a) Sulfur is bright yellow. (b) Silicon is a hard substance. (c) At low temperatures, mercury exists in the solid state. (d) Cadmium is corroded by acids. (e) Hydrogen explodes when ignited in the air.

3. Classify each as a physical or chemical change: (a) formation of an ice cube from liquid water, (b) frying an egg, (c) fizzing of an Alka-Seltzer tablet in water, (d) gasoline evaporating, (e) distillation of alcohol, (f) digesting food, (g) heating a metal until it is red hot.

4. Classify each of the following as a chemical or physical change. (a) Paper ignites when placed in a flame. (b) Sand and water are separated when passed through a filter. (c) Charcoal burns leaving ashes. (d) Skin tans when exposed to the sun. (e) Sugar dissolves in water. (f) Dry ice forms a vapor "cloud" when exposed to the air.

5. Consider the following properties of diamond (a pure form of C): (a) good conductor of heat, (b) electric insulator, (c) density = 3.51 g/cm3, (d) chemically inert, (e) extremely hard, (f) burns in oxygen to produce carbon dioxide. Classify each of the listed properties of diamond as physical or chemical.

6. From each of the following pairs, determine the substance that has the higher viscosity: (a) water or vegetable oil, (b) motor oil or antifreeze, (c) pudding or soft drink, (d) shaving cream or milk

7. Identify the state(s) of matter with each of the following properties: (a) highest average density, (b) lowest viscosity, (c) intermediate densities, (d) constant volume, (e) takes the volume of the bottom of its container, (f) strongest forces among particles

8. What physical state of matter is most commonly found under each of the following conditions: (a) high temperatures and low pressures, (b) low temperatures and high pressures?

9. What type(s) of matter possesses the following properties: (a) has a variable composition with one phase, (b) is inseparable by chemical means, (c) exhibits two or more phases, (d) changes state at constant temperature and its components can be separated chemically, (e) is composed of uncombined atoms?

10. Classify each of the following as pure substances or mixtures. (a) wine, (b) beef, (c) diamond, (d) tap water, (e) charcoal, (f) baking soda, (g) sugar cube

11. Write the name for each of the following elements. (a) He, (b) Fe, (c) Li, (d) Se, (e) Ne, (f) Zr, (g) Mg

12. Write the name for each of the following elements. (a) Hg, (b) Zn, (c) W, (d) Xe, (e) Sr, (f) Ge, (g) Kr

13. Give the symbols for each of the following elements: (a) chromium, (b) silicon, (c) chlorine, (d) potassium, (e) manganese, (f) platinum, (g) rubidium

14. Write the symbols for all eight elements in the second period of the periodic table.

15. Write the names for all elements in the second chemical group (IIA) on the periodic table.

16. State the name and number of each atom in the following formulas. (a) Na2O, (b) N2O5, (c) Li2CO3, (d) RbH2PO4, (e) Al(OH)3

17. From the given information, classify each of the following as an element or a compound. (a) Melts at 120oC, boils at 228oC, and decomposes to Si and I, (b) A white solid that melts at 44oC, and combines with oxygen to form P2O5, (c) A soft, silvery metal that reacts violently with water.

18. Classify each of the following as homogeneous or heterogeneous mixtures. (a) ocean water, (b) iced tea, (c) concrete, (d) motor oil, (e) olive oil and vinegar

19. How is a mixture of alcohol and water separated?

20. (a) What two factors are directly related to an object's kinetic energy? (b) How is the kinetic energy of an object calculated?

21. What type(s) of potential energy is possessed by each of the following? (a) TNT, (b) apple on a tree, (c) wound watch mainspring, (d) stretched rubber band, (e) water at the top of a dam

22. For each of the following pairs, select the one that can transfer the largest quantity of heat. (a) match flame or bunsen burner flame, (b) cup of water at 90oC or bath tub filled with 90oC water, (c) teaspoon of boiling water or gallon of water at 75oC, (d) two identical metal blocks in contact with each other?

23. (a) If 12 g of carbon are exactly combined with 32 g of oxygen, how many grams of carbon dioxide form? (b) What law does this illustrate?

24. What energy transformations occur when electricity is produced through hydroelectric generation?



Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |

ANSWERS TO REVIEW EXERCISE

1. (a) physical, (b) physical, (c) chemical, (d) chemical, (e) chemical

2. (a) physical, (b) physical, (c) physical, (d) chemical, (e) chemical

3. (a) physical, (b) chemical, (c) chemical, (d) physical, (e) physical, (f) chemical, (g) physical

4. (a) chemical, (b) physical, (c) chemical, (d) chemical, (e) physical, (f) physical

5. (a) physical, (b) physical, (c) physical, (d) chemical, (e) physical, (f) chemical

6. (a) vegetable oil, (b) motor oil, (c) pudding, (d) shaving cream

7. (a) solid, (b) gas, (c) liquid, (d) solid, liquid, (e) liquid, (f) solid

8. (a) gas, (b) solid

9. (a) homogeneous mixture, (b) element, (c) heterogeneous mixture, (d) compound, (e) element

10. (a) mixture, (b) mixture, (c) pure substance, (d) mixture, (e) mixture, (f) pure substance, (g) pure substance

11. (a) helium, (b) iron, (c) lithium, (d) selenium, (e) neon, (f) zirconium, (g) magnesium

12. (a) mercury, (b) zinc, (c) tungsten, (d) xenon, (e) strontium, (f) germanium, (g) krypton

13. (a) Cr, (b) Si, (c) Cl, (d) K, (e) Mn, (f) Pt, (g) Rb

14. Li, Be, B, C, O, N, F, Ne

15. beryllium, magnesium, calcium, strontium, barium, radium

16. two sodium atoms and one oxygen atom, (b) two nitrogen and five oxygen atoms, (c) two lithium, one carbon, and three oxygen atoms, (d) one rubidium, two hydrogen, one phosphorus, and four oxygen atoms, (e) one aluminum, three oxygen, and three hydrogen atoms

17. (a) compound, (b) element, (c) element

18. (a) homogeneous, (b) heterogeneous, (c) heterogeneous, (d) homogeneous, (e) heterogeneous

19. The lower boiling alcohol evaporates more readily than water when heated. Then, cool the alcohol vapor and condense it back to a liquid.

20. (a) mass and velocity, (b) KE = 1/2 mv2

21. (a) chemical, (b) chemical and positional, (c) conditional, (e) positional

22. (a) bunsen burner flame, (b) bath tub, (c) gallon of water, (d) neither

23. (a) 44 g CO2, (b) law of conservation of mass

24. potential energy of water, kinetic energy of water, mechanical energy, electrical energy
 

Section | 1.1 (Chemistry) | 1.2 (Matter) | 1.3 (States) | 1.4 (Classification) | 1.5 (Energy) | 1.6 (Conservation) | Summary | Review Exercise | Answers | TopReturn to WWWolfe |