Question

What is the change in internal energy when a gas contracts from $377$ mL to $177$ mL under a constant pressure of 2 atm, while at the same time being cooled by removing $124J$ heat?
[Take: $1Latm$ = $100J$]

• A. $-24J$
• B. $-84J$
• C. $-164J$
• D. $-24J$

Answer 1

The correct option is B $-84J$

From the first law of thermodynamics,
$△U=Q+W$
$Q=-124J$ (given)
$W=-P_{ext}(v_2-v_1)$
$-2(177-377)=400atmmL=0.4atmL$

Since, $1atmL=100J$
$0.4atmL=40J$
Substituting the values of $QandW$, we get,
$△U=-124+40=-84J$