Question

4. The internal energy of the system decreases in an adiabatic process. Which of the following must be true regarding this
process?
a) Heat flows out of the system
b) Work is done by the system
c) Work is done on the system
d) The potential energy of the system is changing​

Answer 1

Answer:

(b) Work is done by the system

Answer 2

By first law of thermodynamics,

$\sf{\longrightarrow Q=U+W}$

where,

• $\sf{Q=}$ heat energy supplied to the system

• $\sf{U=}$ internal energy

• $\sf{W=}$ work done by the system

If work is done on the system then $\sf{W}$ will be replaced by $\sf{-W.}$

For an adiabatic process,

$\sf{\longrightarrow Q=0}$

$\sf{\longrightarrow U+W=0}$

$\sf{\longrightarrow W=-U}$

This means work done increases as the internal energy of the system decreases.

Thus we can conclude with that work is done by the system.

Hence (B) is the answer.