Question

Assertion: C_P is always greater than C_V in gases.
Reason: Work done at constant pressure is more than at constant volume.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

When we heat the gas at constant volume, the heat is supplied to raise the temperature of gas only. When we heat the gas at constant pressure, the volume of the gas apart from temperature of the gas rises. When the gas expands, it does some external work for increasing the volume. So in this case, the heat is supplied.
(a) to raise the temperature of the gas.
(b) to do the mechanical work for expansion.
As a result more amount of heat is required to increase the temperature of the gas through the same amount when the pressure is kept constant. Hence $C_p$ is always greater than the value of $C_V$