Content In A Nutshell
 

Humans have been fascinated by gases since prehistoric times. Air was important enough to be considered one of the four elements by Aristotle—but only for about 200 years have scientists been able to distinguish one “air” from another and realize that the air we breathe is actually a mixture of gases.

Gases consist of submicroscopic particles that are relatively far apart from each other moving randomly with an average kinetic energy proportional to the temperature. (The word gas is derived from the Greek chaos.)

Gaseous particles have very little effect on each other; in fact an ideal gas particle is defined as having no volume and no attraction for other particles. We can show by our senses of smell or sight that gases spread out to fill a given volume.

Gases can be described in terms of four variables: pressure, volume, temperature, and amount (moles). Several sets of two variables—pressure and temperature (Gay Lussac’s Law), volume and temperature (Charles’ Law), volume and amount
(Avogadro’s Law), and pressure and amount—are directly proportional, but pressure and volume are inversely proportional (Boyle’s Law). We can use simple logic to understand the relationships among these variables. Because gases are so much a
part of our lives, many examples of these relationships are found in our environment.

The general gas law combines these variables into an equation with a single constant R, the gas law constant. The equation PV = nRT may be used in calculations, assuming students have a background in algebra.

There are other relationships derivable from the gas law. Dalton’s law of partial pressures indicates that the sum of the pressures of two or more gases equals the total pressure. For many years the molar masses of gases and volatile liquids were determined experimentally using the gas laws. Gas densities can also be calculated using these relationships.

From the time of the 18th-century revolution in chemistry, scientists have used the volumes of gases in work involving stoichiometry of reactions. That two volumes of hydrogen react with one volume of oxygen to form two volumes of water vapor helped chemists understand that H 2 and O 2 were diatomic and that H 2 O was a better formula for water than was HO. This knowledge was essential to development of modern atomic theory.
 
 

Many secondary school texts use gases as an introduction to the atomic theory since gases, like atoms, are generally invisible bodies with observable effects. Using gas laws in stoichiometric calculations makes a link between different topics in the study of chemistry.  Whether it is concern with pressure in an automobile tire, the expansion of popcorn on heating, the effect of a leak in a space suit, the understanding of absolute zero, or the solution to environmental problems such as the depletion of the ozone layer, the study of gases enriches the curriculum of high school students.

1. A gas sample is composed of submicroscopic particles moving with an average kinetic energy directly proportional to the temperature (in kelvins).
2. A gas sample may be described in terms of four variables—pressure, temperature, volume, and amount (moles).
3. The general gas law describes relationships among the variables (P, T, V, n) of an ideal gas. Relationships often described in textbooks as Boyle’s law, Gay Lussac’s law, Charles’ law, and Avogadro’s law can be regarded as subsets of the general gas law.
4. The behavior of gases can be explained in terms of the kinetic molecular theory.
5. Gas densities and molar masses can be determined experimentally through applications of the general gas law.
6. Gas particles, when compared with those of liquids and solids, are relatively far apart from one another.

1. Mass, volume, pressure, temperature, amount of substance
2. Energy
3. Molecules and atoms
4. Stoichiometry
5. Variables, constants
6. Density
7. Molar mass

1. Problem solving
2. Algebra
3. Measurement
4. Graphing
5. Temperature scales
 

After completing their study of gases, students should be able to:
1. imagine gases moving in a given volume at a given temperature and describe the behavior of an ideal gas.
2. define and/or explain the meaning of pressure, temperature, volume, and amount of substance (moles).
3. predict the result of changes involving two variables (P, V, n or T) when others are held constant.
4. use the general gas law in calculations, either in one- or two-condition problems.
5. use the general gas law to calculate molar mass and gas density.
6. understand the importance of gases in the environment.
7. recognize and discuss environmental problems concerning atmospheric gases or global warming.