Question

When a real gas expands adiabatically against a finite pressure, its

• A. internal energy increases
• B. internal energy decreases
• C. temperature always increases
• D. internal energy remains constant

Answer 1

The correct option is B internal energy decreases

From the first law of thermodynamics,
$dU=q+W$
In adibatic process no change of heat takes place.
So, $dU=W$
Since, the gas is expanding, the work is done by the gas.
$dU=-W$.
Hence internal energy of the system decreases.
Again, $dU=C_v(T_2-T_1)=W$
Since here W is negative, so $T_1>T_2$.
So temperature will also decrease.