Answer to Question #262529 in Mechanical Engineering for Angel

Question

Explain briefly why a gas has two specific heat capacities.

0.28 kg of a gas is heated from 29 °C to 68°C. The specific heat capacity of the gas at constant volume is Cv = 0.72 kJ/kgK and the specific heat capacity at constant pressure Cp =1.01 kJ/kgK Calculate the change in:

a) Enthalpy

b)Internal energy

c) Flow energy

Answer 1

A solid or a liquid when heated does not undergo any change in the volume or pressure. But in case of a gas, both the pressure and the volume change on heating. Therefore, specific heat of a gas is defined either at constant volume or at constant pressure and hence a gas has two specific heats.

q =0.28 kg • 0.72 kJ/kgK • (68°C - 29°C) = 7.86 kJ