http://www.ck12.org Chapter 14. The Properties of Gases
Introduction
FIGURE 14.5
Soap bubble in flight.In the last lesson, we studied the properties and characteristics of gases. Many of these properties can be explained by
the fact that gases are mostly empty space but contain large numbers of particles with certain masses and velocities.
Now we are going to study how gases behave when exposed to changes in temperature, pressure, and volume. We
will also see how the development of instruments that measure pressure and temperature led to new discoveries in
our understanding of gases. The origins of the absolute temperature scale will be discussed, and we will examine the
empirical relationships between volume, temperature, pressure, and amount that were discovered by early chemists.
Boyle’s Law: Pressure vs. Volume
With the development of the barometer in 1644 came a series of experiments and investigations aimed at under-
standing the nature of gases. Robert Boyle (1627-1691) was particularly interested in the relationships between the
volume occupied by a sample of gas and the pressure it exerted on its container. He invented one of the earliest air
pumps, which allowed him to create low-pressure environments. Boyle devised experiments to study the pressure-
volume relationship. For example, he observed that reducing the volume of a balloon by half doubles its volume. In
other words, volume is inversely proportional to pressure (V∝1/P).
For a fixed amount of gas at a constant temperature, the volume occupied is inversely proportional to its pressure.
Stated mathematically, the product of the pressure and volume is equal to a constant:
P×V=k
wherekis a constant that depends on the temperature and amount of the gas in a given sample. This observation
was published in 1662 and is now known asBoyle’s Law.
This equation can be used to quantitatively predict how changes in pressure will affect the volume of a sample, and
vice versa. Let’s assume that a sample of gas undergoes a change to one of these variables while the temperature and
amount are held constant. The initial pressure (P 1 ) and the initial volume (V 1 ) can be related to the final pressure
(P 2 ) and the final volume (P 2 ) as follows:
P 1 ×V 1 =k