Chapter 14 Laboratory: Gas Chemistry 245

Laboratory:

Gas Chemistry

The study of gases and their chemistry, composition, properties, and interactions is an

important part of general chemistry. By their nature, gases are more difficult to study than

solids and liquids. Unlike solids and liquids, which tend to stay put in their containers, gases

dissipate rapidly into the surrounding atmosphere. (Imagine studying liquids if you had to

work under water.) Their low density relative to solids and liquids makes it difficult to weigh

small volumes of gases accurately. Many gases are colorless and impossible to discriminate

visually or by odor.

Despite these difficulties, gases have been studied intensively since chemistry evolved as

a separate science in the late eighteenth century. Pioneers like Antoine-Laurent de Lavoisier,

Carl Wilhelm Scheele, Joseph Priestley, and Joseph Louis Gay-Lussac built on the earlier

work of the seventeenth-century natural philosopher Robert Boyle to discover and explore

the basic principles that govern the behavior of gases.

Naturally enough, early chemists thought of all gases as forms of air. As they isolated

various gases experimentally—such as hydrogen, oxygen, carbon dioxide, chlorine, and

others—in relatively pure forms, it soon became obvious that these new forms of “air” had

properties much different from plain old air-air. Immersing a candle in oxygen, for example,

caused it to burn fiercely, and carbon dioxide snuffed it out instantly. Accordingly, the early

chemists named gases as airs with particular properties, not recognizing that each of these

special “airs” was in fact a discrete chemical element or compound. It was not until the

seminal works of Scheele, Lavoisier, and Priestley were published that scientists recognized

that these newfangled gases were in fact discrete chemical elements and compounds.

In addition to studying their chemical properties, these early gas chemists also studied the

physical properties of gases; in particular, the relationships between volume, pressure, and

temperature. Anyone who has used a manual pump to inflate a tire or a basketball intuitively

understands the relationship of these three characteristics of gases. As the plunger is

depressed, the pressure increases, the volume decreases, and the pump gets noticeably

warmer. When you used canned air, the opposite occurs. When you press the trigger, gas is

released, increasing its volume and reducing its pressure, and the can gets noticeably colder,

a phenomenon known as the Joule-Thompson effect.

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