Question

In a given process of an ideal gas, dW = 0 and dQ< 0. Then for the gas –

• A. The temperature will decrease
• B. The volume will increase
• C. The pressure will remain constant
• D. The temperature will increase

Answer 1

Answer: (A)

The temperature will decrease

Answer 2

From first law of thermodynamics,

dQ = dU + dW

dQ = dU if dW = 0

Since, dQ < 0

Therefore, dU < 0 or U_final < U_initial

or temperature will decrease.

Note : Internal energy U of an ideal gas depends only on the temperature of the gas. Internal energy of 'n' moles of an ideal gas is given by

U = n(f/2)RT

U µ T

Here, f is the degree of freedom of the gas.