Define two principal specific heats of a gas. Which is greater and why?
Answers
The principal specific heat capacities of a gas
The specific heat capacity of a gas will depend on the conditions under which it is measured and since these could vary considerably we will restrict ourselves to the following, called the principal specific heat capacities of a gas:
(a) The specific heat capacity at constant volume (cv) is defined as the quantity of heat required to raise the temperature of 1 kg of the gas by 1 K if the volume of the gas remains constant.
(b) The specific heat capacity at constant pressure (cp) is defined as the quantity of heat required to raise the temperature of 1 kg of the gas by 1 K if the pressure of the gas remains constant.
The specific heat capacity at constant pressure (cp) is always greater than that at constant volume (cv), since if the volume of the gas increases work must be done by the gas to push back the surroundings.