Question

The value of internal energy in an adiabatic process

• A. Remains unchanged
• B. Only increases
• C. Only diminishes
• D. May diminish and may also increase

Answer 1

Answer: (D)

May diminish and may also increase

In an adiabatic process, $\Delta Q=0J$

From 1st law of thermodynamics,

$\Delta Q=\Delta U+\Delta W$

$0=\Delta U+\Delta W$

$\Delta U=-\Delta W=-P\Delta V$. . . . . . .(1)

At constant volume, $V=constant$

$\Delta V=0$

From equation (1),

$\Delta U=0J$

Change in internal energy is temperature dependent. So, change in internal energy at constant volume

$\Delta U=m{C}_V\Delta T$. . . . . .(2)

From equation (1) and (2), we conclude that internal energy in adiabatic process may diminish at constant volume and may also increases.

The correct option is D.