Question

If Cp and Cv are the specific heats for a gas at constant pressure and at constant volume respectively, then the relation Cp-Cv=R is exact for?

(a) Ideal and real gases at all pressures

(b) Ideal gas at all pressures and real gas at a moderate pressure

(c) Ideal gas and nearly true for real gases at high pressure

(d) Ideal gas and nearly true for real gases at a moderate pressure

This question was addressed to me during an interview.

This interesting question is from Isothermic and Adiabatic Process topic in section Kinetic Theory of Gases of Engineering Physics I

Answer 1

Right option is (d) Ideal gas and nearly true for real gases at a moderate pressure

To elaborate: Cp-Cv=R

Holds for ideal gas and for real gases at moderate pressure.