General_Chemistry_whitten full.pdf

The Foundations

of Chemistry

OUTLINE

1-1 Matter and Energy

1-2 States of Matter

1-3 Chemical and Physical Properties

1-4 Chemical and Physical Changes

1-5 Mixtures, Substances,

Compounds, and Elements

1-6 Measurements in Chemistry

1-7 Units of Measurement

1-8 Use of Numbers

1-9 The Unit Factor Method

(Dimensional Analysis)

1-10 Percentage

1-11 Density and Specific Gravity

1-12 Heat and Temperature

1-13 Heat Transfer and the

Measurement of Heat

The earth is a huge chemical

system, including innumerable

reactions taking place constantly,

with some energy input from

sunlight. The earth serves as the

source of raw materials for all

human activities as well as the

depository for the products of these

activities. Maintaining life on the

planet requires understanding and

intelligent use of these resources.

Scientists can provide important

information about the processes, but

each of us must share in the

responsibility for our environment.

OBJECTIVES

After you have studied this chapter, you should be able to

• Use the basic vocabulary of matter and energy

• Distinguish between chemical and physical properties and between chemical and

physical changes

• Recognize various forms of matter: homogeneous and heterogeneous mixtures,

substances, compounds, and elements

• Apply the concept of significant figures

• Apply appropriate units to describe the results of measurement

• Use the unit factor method to carry out conversions among units

• Describe temperature measurements on various common scales, and convert between

these scales

• Carry out calculations relating temperature change to heat absorbed or liberated

T housands of practical questions are studied by chemists. A few of them are

How can we modify a useful drug so as to improve its effectiveness while mini-

mizing any harmful or unpleasant side effects?

How can we develop better materials to be used as synthetic bone for replacement

surgery?

Which substances could help to avoid rejection of foreign tissue in organ transplants?

What improvements in fertilizers or pesticides can increase agricultural yields? How

can this be done with minimal environmental danger?

How can we get the maximum work from a fuel while producing the least harmful emis-

sions possible?

CHAPTER 1: The Foundations of Chemistry

Which really poses the greater environmental threat — the burning of fossil fuels and

its contribution to the greenhouse effect and climatic change, or the use of nuclear

power and the related radiation and disposal problems?

How can we develop suitable materials for the semiconductor and microelectronics in-

dustry? Can we develop a battery that is cheaper, lighter, and more powerful?

What changes in structural materials could help to make aircraft lighter and more eco-

nomical, yet at the same time stronger and safer?

What relationship is there between the substances we eat, drink, or breathe and the

possibility of developing cancer? How can we develop substances that are effective in

killing cancer cells preferentially over normal cells?

Can we economically produce fresh water from sea water for irrigation or consump-

tion?

How can we slow down unfavorable reactions, such as the corrosion of metals, while

speeding up favorable ones, such as the growth of foodstuffs?

Chemistry touches almost every aspect of our lives, our culture, and our environment. Its

scope encompasses the air we breathe, the food we eat, the fluids we drink, our clothing,

dwellings, transportation and fuel supplies, and our fellow creatures.

Chemistry is the science that describes matter — its properties, the changes it un-

dergoes, and the energy changes that accompany those processes.

Enormous numbers of chemical

reactions are necessary to produce

a human embryo (here at 10 weeks,

6 cm long).

Matter includes everything that is tangible, from our bodies and the stuff of our every-

day lives to the grandest objects in the universe. Some call chemistry the central science.

It rests on the foundation of mathematics and physics and in turn underlies the life

sciences — biology and medicine. To understand living systems fully, we must first

understand the chemical reactions and chemical influences that operate within them. The

chemicals of our bodies profoundly affect even the personal world of our thoughts and

emotions.

No one can be expert in all aspects of such a broad science as chemistry. Sometimes

we arbitrarily divide the study of chemistry into various branches. Carbon is very versa-

tile in its bonding and behavior and is a key element in many substances that are essen-

tial to life. All living matter contains carbon combined with hydrogen. The chemistry of

compounds of carbon and hydrogen is called organic chemistry. (In the early days of

chemistry, living matter and inanimate matter were believed to be entirely different. We

now know that many of the compounds found in living matter can be made from non-

living, or “inorganic,” sources. Thus, the terms “organic” and “inorganic” have different

meanings than they did originally.) The study of substances that do not contain carbon

combined with hydrogen is called inorganic chemistry. The branch of chemistry that is

concerned with the detection or identification of substances present in a sample ( qualita-

tive analysis ) or with the amount of each that is present ( quantitative analysis ) is called

analytical chemistry. Physical chemistry applies the mathematical theories and

methods of physics to the properties of matter and to the study of chemical processes and

the accompanying energy changes. As its name suggests, biochemistry is the study of

the chemistry of processes in living organisms. Such divisions are arbitrary, and most

chemical studies involve more than one of these traditional areas of chemistry. The

principles you will learn in a general chemistry course are the foundation of all branches

of chemistry.

CHAPTER 1: The Foundations of Chemistry

We understand simple chemical systems well; they lie near chemistry’s fuzzy boundary

with physics. They can often be described exactly by mathematical equations. We fare less

well with more complicated systems. Even where our understanding is fairly thorough,

we must make approximations, and often our knowledge is far from complete. Each year

researchers provide new insights into the nature of matter and its interactions. As chemists

find answers to old questions, they learn to ask new ones. Our scientific knowledge has

been described as an expanding sphere that, as it grows, encounters an ever-enlarging

frontier.

In our search for understanding, we eventually must ask fundamental questions, such

as the following:

How do substances combine to form other substances? How much energy is involved

in changes that we observe?

How is matter constructed in its intimate detail? How are atoms and the ways that they

combine related to the properties of the matter that we can measure, such as color,

hardness, chemical reactivity, and electrical conductivity?

What fundamental factors influence the stability of a substance? How can we force a

desired (but energetically unfavorable) change to take place? What factors control the

rate at which a chemical change takes place?

In your study of chemistry, you will learn about these and many other basic ideas that

chemists have developed to help them describe and understand the behavior of matter.

Along the way, we hope that you come to appreciate the development of this science, one

of the grandest intellectual achievements of human endeavor. You will also learn how to

apply these fundamental principles to solve real problems. One of your major goals in the

study of chemistry should be to develop your ability to think critically and to solve prob-

lems (not just do numerical calculations!). In other words, you need to learn to manipu-

late not only numbers, but also quantitative ideas, words, and concepts.

In the first chapter, our main goals are (1) to begin to get an idea of what chemistry is

about and the ways in which chemists view and describe the material world and (2) to

acquire some skills that are useful and necessary in the understanding of chemistry, its

contribution to science and engineering, and its role in our daily lives.

1-1

MATTER AND ENERGY

We might say that we can “touch” air

when it blows in our faces, but we

depend on other evidence to show that

a still body of air fits our definition of

matter.

Matter is anything that has mass and occupies space. Mass is a measure of the quantity

of matter in a sample of any material. The more massive an object is, the more force is

required to put it in motion. All bodies consist of matter. Our senses of sight and touch

usually tell us that an object occupies space. In the case of colorless, odorless, tasteless

gases (such as air), our senses may fail us.

Energy is defined as the capacity to do work or to transfer heat. We are familiar with

many forms of energy, including mechanical energy, light energy, electrical energy, and

heat energy. Light energy from the sun is used by plants as they grow, electrical energy

allows us to light a room by flicking a switch, and heat energy cooks our food and warms

our homes. Energy can be classified into two principal types: kinetic energy and poten-

tial energy.

A body in motion, such as a rolling boulder, possesses energy because of its motion.

Such energy is called kinetic energy. Kinetic energy represents the capacity for doing

work directly. It is easily transferred between objects. Potential energy is the energy an

The term comes from the Greek word

kinein, meaning “to move.” The word

“cinema” is derived from the same

Greek word.

1-1 Matter and Energy

object possesses because of its position, condition, or composition. Coal, for example,

possesses chemical energy, a form of potential energy, because of its composition. Many

electrical generating plants burn coal, producing heat, which is converted to electrical

energy. A boulder located atop a mountain possesses potential energy because of its height.

It can roll down the mountainside and convert its potential energy into kinetic energy.

We discuss energy because all chemical processes are accompanied by energy changes. As

some processes occur, energy is released to the surroundings, usually as heat energy. We

call such processes exothermic. Any combustion (burning) reaction is exothermic. Some

chemical reactions and physical changes, however, are endothermic; that is, they absorb

energy from their surroundings. An example of a physical change that is endothermic is

the melting of ice.

Nuclear energy is an important kind of

potential energy.

The Law of Conservation of Matter

When we burn a sample of metallic magnesium in the air, the magnesium combines with

oxygen from the air (Figure 1-1) to form magnesium oxide, a white powder. This chem-

ical reaction is accompanied by the release of large amounts of heat energy and light

energy. When we weigh the product of the reaction, magnesium oxide, we find that it is

heavier than the original piece of magnesium. The increase in the mass of a solid is due

to the combination of oxygen from the air with magnesium to form magnesium oxide.

Many experiments have shown that the mass of the magnesium oxide is exactly the sum

of the masses of magnesium and oxygen that combined to form it. Similar statements can

be made for all chemical reactions. These observations are summarized in the Law of

Conservation of Matter:

There is no observable change in the quantity of matter during a chemical reaction

or during a physical change.

This statement is an example of a scientific (natural) law, a general statement based on

the observed behavior of matter to which no exceptions are known. A nuclear reaction is

not a chemical reaction.

Figure 1-1 Magnesium burns in

the oxygen of the air to form magne-

sium oxide, a white solid. The mass

of magnesium oxide formed is equal

to the sum of the masses of oxygen

and magnesium that formed it.

The Law of Conservation of Energy

In exothermic chemical reactions, chemical energy is usually converted into heat energy.

Some exothermic processes involve other kinds of energy changes. For example, some lib-

erate light energy without heat, and others produce electrical energy without heat or light.

In endothermic reactions, heat energy, light energy, or electrical energy is converted into

chemical energy. Although chemical changes always involve energy changes, some energy

transformations do not involve chemical changes at all. For example, heat energy may be

converted into electrical energy or into mechanical energy without any simultaneous

chemical changes. Many experiments have demonstrated that all of the energy involved

in any chemical or physical change appears in some form after the change. These obser-

vations are summarized in the Law of Conservation of Energy:

Electricity is produced in hydroelectric

plants by the conversion of mechanical

energy (from flowing water) into

electrical energy.

Energy cannot be created or destroyed in a chemical reaction or in a physical change.

It can only be converted from one form to another.

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