The Ideal Gas and Kinetic Theory
The States of Matter
|It is very fruitful, in general, in the physical sciences to put physical formulas at play in your imagination. Imagine the system described undergoing the changes modeled by the formula. What does the formula tell you? For the Ideal Gas Law, it is helpful to imagine the behavior of the system composed of an ideal gas successively subjected to various constraints. What would happen if the system were compressed at constant temperature? The answer is Boyle's Law, the product of the pressure and volume remains constant. What happens with heating at constant pressure? As the temperature increases at constant pressure, Charles' Law describes the changes that occur, the volume increases.|
Similar reasoning can also be applied to understand how the Ideal Gas Law implies the Combined Gas Law and Gay-Lussac's Law. It is also helpful, furthermore, to go beyond interpreting the laws as a consequence of manipulating equations. Boyle's Law, Charles' Law and Gay-Lussac's Law were all discovered prior to the Ideal Gas Law. Use what you know of kinetic theory to imagine the particle level of a model thermodynamic system (the molecular level) and try to imagine the transformations described by the laws. For a constant temperature compression, for example, as described by Boyle's Law, we know that the average kinetic energy per particle is constant, so the vigor of molecular motion is not changed between the initial and final state. What has changed? The system has been compressed. There is less volume, so the gas is more dense; i.e. if we were to test the pressure with a piston barometer, more collisions would occur upon its surface, and higher pressure would be registered.