Question

A gas undergoes a change from state A to state B. In this process, the heat absorbed and work done by the gas is 5 J and 8 J, respectively. Now gas is brought back to A by another process during which 3 J of heat is evolved. In this reverse process of B to A:

• A. 10 J of the work will be done by the gas.
• B. 6 J of the work will be done by the gas.
• C. 10 J of the work will be done by the surrounding on gas.
• D. 6 J of the work will be done by the surrounding on the gas.

Answer 1

The correct option is D 6 J of the work will be done by the surrounding on the gas.

According to the first law of thermodynamics,

$\Delta U=q+w=5-8=-3J$

As, the internal energy is a state function, for the reverse process $\Delta U$ should be equal to $3J$.

$\Delta U=q+w$

$+3=-3+w$

$\Rightarrow w=+6J$

As work done has a positive sign, work is done by the surrounding on the gas.

Hence, the correct option is $D$