Consider two identical flasks filled with an ideal gas at different temperatures that can undergo different thermodynamic processes. Suppose, in a constant-volume process, the first flask's gas temperature is increased to equate to the temperature of the second flask. Then, its internal energy will be the same as the heat change and can be written in terms of molar heat capacity. In a constant-pressure process, if the temperature is increased by the same amount, then the system's internal energy changes with some work being done. As the internal energy is a state function, the internal energy change of the system is the same under both processes. Using the ideal gas equation in differential form, the work done can be written in terms of temperature change. By canceling the common factors on both sides, the relation between the molar heat capacities for both processes is obtained. Here, R is the universal gas constant, and hence, the molar heat capacity of an ideal gas under a constant-pressure process is always greater than that under a constant-volume process.