In the formula of the general gas law, for a given mass of gas where PV = mRT, r is:

In the general gas law formula ( PV = mRT ), the variable ( r ) represents a specific gas constant that is characteristic of the specific gas being considered. This specific gas constant is derived from the universal gas constant ( R ) divided by the molar mass of the gas, allowing it to be expressed in units of kJ/(kg·K).

This relationship is essential for calculations involving the properties of gases under different conditions of pressure and temperature. The specific gas constant allows for the determination of specific properties of the gas, such as density and specific volume, based on the gas’s state. The units of kJ/(kg·K) indicate that the value of ( r ) is specific to the substance being measured, making it crucial for accurately applying the ideal gas law in thermodynamic calculations.

Understanding that ( r ) is a characteristic constant reinforces the importance of identifying the specific gas in use during calculations, leading to correct interpretations of the behavior of gases in various engineering contexts.