What is the Ideal Gas Law? The Ideal Gas Law is a highly useful formula that can used to calculate the volume, pressure, temperature, or number of moles of an "ideal gas" when the other three variables are known. It is given as: PV = nRT where P is pressure, V is volume, n is the number of moles, R is the universal gas constant equal to approximately 0.0821 L x atm / K x mol, and T is the temperature in Kelvin. Because the ideal gas law is a proportion, if any of the variables is held constant, it can be omitted from the equation. See Boyle's Law, Charles's Law, Gay - Lussac's Law, and Avogadro's Law.
So what's an "ideal" gas? An ideal gas is a hypothetical construct that describes the approximate behavior of most gases at low pressure and high temperature. However, no gas will exactly follow the ideal gas law because the ideal gas law does not account for the mass of the gas molecules and interparticle interactions. The Real Gas Law must be used in order to refine calculations to take these variables into account.
Ideal Gas Law LimitationsThe ideal gas law works best when the gas particles are at low pressures and high temperatures. At these conditions, the concepts of the kinetic molecular theory are most true. However, at high pressures and low temperatures, there occur deviations from KMT and the ideal gas laws. Gas particles at these conditions are much closer together, allowing some attraction and repulsion to exist. Also, though gases are assumed to be negligible, at high pressures and low temperatures, this is no longer assumed true. As a result, some of the ideal gas laws may not hold true, such as Dalton's law. At these conditions, attractions may occur, altering the pressure of the gases. For Avogadro's Law, these attractions could alter the number of moles that could fit within a certain volume. Thus, the real gas laws exist.