Ideal Gas Equation

The relationship among a gas's pressure, volume and (absolute) temperature is called the ideal gas equation. Using absolute temperature, the classical gas laws take particularly simple forms:

Charles' law: at constant pressure, the volume-temperature graph (Fig. 7.2(b)) passes exactly through the origin if temperature is measured on the Kelvin scale, so $V \propto T$, i.e. $V/T = \text{constant}$ --- (7.4). In words: the volume of a fixed mass of gas is directly proportional to its absolute temperature, at constant pressure.

Pressure law (Gay Lussac's law): similarly, $P \propto T$, i.e. $P/T = \text{constant}$ --- (7.5) -- the pressure of a fixed mass of gas is directly proportional to its absolute temperature, at constant volume.

Boyle's law: at constant temperature, pressure and volume of a fixed mass of gas are inversely proportional, $P \propto 1/V$, i.e. $PV = \text{constant}$ --- (7.6). …