Question

For an ideal gas:
A. The change in internal energy in a constant pressure process from temperature $T _{1}$ to $T _{2}$ is equal to $nC _{ v }\left( T _{2}\right.$ $\left.- T _{1}\right),$ where $C _{ v }$ is the molar specific heat at constant volume and $n$ the number of moles of the gas.
B. The change in internal energy of the gas and the work done by the gas are equal in magnitude in an adiabatic process.
C. The internal energy does not change in an isothermal process.
D. No heat is added or removed in an adiabatic process.
Which of the combination are correct?

• A. A, B
• B. A, B, C
• C. A, B, C, D
• D. A, C

Answer 1

Answer: (C)

Change in internal energy depends only on change in temperature since internal energy is a function of state only,
i.e., $dU = nC _{ v } dT$.
In adiabatic process, $dQ =0$
Hence, $d U+d W=0$
$ \Rightarrow d U=-d W$
i.e., magnitude of change in internal energy is equal to magnitude of work done.