Question

A gas is compressed from a volume of $2m^3$ to volume of $1m^3$ at the constant pressure of 100 N / $m^2$. Then it is heated at constant volume by supplying 150 J of energy. As a result, the internal energy of the gas:

• A. Increases by 250 J
• B. Decreases by 250 J
• C. Increases by 50 J
• D. Decreases by 50 J

Answer 1

The correct option is A Increases by 250 J

Work done in compressing the gas at constant pressure is given by :-

$W=PAV=100\times (1-2)=-100J$

also, heat supplied to system, $Q=150J$

from first law of thermodynamics,

$△u=Q-W$ $\therefore$ change in internal energy $\left(△u\right)=250J$

$\Rightarrow △u=150-(-100)=250J$