Question

In a thermodynamic process of mass of a gas is changed in such a manner gas releases $20$ $joules$ of heat and $8$ $joules$ of was done on the gas. If the energy of the gas was $30$ $joules$, then the energy will be:-

• A. $2$ $J$
• B. $42$ $J$
• C. $18$ $J$
• D. $58$ $J$

Answer 1

Answer: (C)

$18$ $J$

$\text{given}:$

$dQ$ = -20 J ( engergy is released)

$dW$ = -8 J ( work is done on the gas )

$Uo$ = 30 J

$\text{Solution}:$

from the third law of thermodynamics

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

putting all the values from the given we get

$\Rightarrow$ -20 +8= -12J

$U^{\prime }-Uo$ =$\Delta$ $U$

30 - 12 = 18

HENCE ,THE CORRECT OPT: C