Charles' Law

Air is a gas. Gases have various properties that we can observe with our senses, including the gas pressure, temperature (T), mass, and the volume (V) that contains the gas. Careful, scientific observation has determined that these variables are related to one another and that the values of these properties determine the state of the gas. The relationship between temperature and volume, at a constant number of moles and pressure, is called Charles and GayLussac's Law in honor of the two French scientists who first investigated this relationship. Charles did the original work, which was verified by Gay-Lussac. They observed that if the pressure is held constant, the volume V is equal to a constant times the temperature T

V = constant * T

CHARLES’ LAW “The volume of a quantity of a gas, held at constant pressure, varies directly as the absolute temperature.”

How Volume Varies With Temperature If we place a balloon in liquid nitrogen it shrinks: So, gases shrink if cooled. Conversely, if we heat a gas it expands (as in a hot air balloon). Let’s take a closer look at temperature before we try to find the exact relationship of V vs. T.

Temperature vs. Volume Graph (fig.7,8 pg.430)

30 25

Volume

20 15

10 5

– 273

0 Temperature (°C)

100