Ideal Gas Law and Gas Equilibria

The Ideal Gas Law

The ideal gas law can be used to solve most gas equilibrium problems found on the MCAT. The ideal gas law equation follows the kinetic molecular theory, and is represented by:

$PV = nRT$

P is pressure measured in atmospheres. V is volume measured in liters. n is the number of moles of the substance. R is the universal gas constant. T is the temperature in Kelvin.

Gas Equilibria

There are three laws that are derivatives of the ideal gas law. You don’t have to remember the names of the laws or the origins. However, you should know these laws and be able to see the relationship between the ideal gas law and the equations that represent them.

Charles’ Law

Charles’ Law states that the volume of gas is proportional to its temperature at a constant pressure.

Boyle’s Law

Boyle’s Law states that the volume of a gas is inversely proportional to pressure at constant temperature.

Avogadro’s Law states that the volume of gas is proportional to the number of moles of gas at constant temperature and pressure.

Ideal Gas Properties

There are two laws that describe the properties and behaviors of ideal gases – Dalton’s Law and Graham’s Law.

Dalton’s Law

Dalton’s Law states that the total pressure exerted by a gaseous mixture is the sum of the partial pressures of each of its gases.

$P_{total} = P_{1} + P_{2} + P_{3}...$

Graham’s Law

Graham’s Law states that the rate at which gases diffuse is inversely proportional to the square root of their densities. This ratio is represented by the following equation:

$\frac{ v_{1} } {v_{2}} = \frac{\sqrt{m_{1}}} {\sqrt{m_{2}}}$