Question

$50J$ heat is supplied to a gaseous system simultaneously the gas expands against external pressure $2atm$ by $0.8L$. The change in internal energy of the system will be:

• A. $-120.8J$
• B. $-112.11J$
• C. $-125.4J$
• D. $-130.60J$

Answer 1

The correct option is B $-112.11J$

Solution:- (B) $-112.11J$

Given that the heat is supplied to the system.

Therefore,

$q=50J$

Given:-

$P_{ext.}=2atm$

$\Delta V=0.8L$

As we know that,

$w=-P\Delta V$

$\Rightarrow w=-2\times 0.8=-1.6L-atm=-162.11J$

Now from first law of thermodynamics,

$\Delta U=q+w$

$\Rightarrow \Delta U=50+(-162.128)=-112.11J$

Hence the change in internal energy of the system will be $-112.11J$.