Question

A vessel contains $100$ litres of a liquid X. Heat is supplied to the liquid at a constant pressure of $1$ atm in such a fashion that heat given is equal to the change in enthalpy of the system. The volume of the liquid increases by $2$ litres. If $202.6$ joules of heat were supplied, then the values of $△U$ and $△H$ would have been:
$[△U=\text{change in internal energy},△H\text{change in enthalpy}]$

• A. $△U=0,△H=0$
• B. $△U=+202.6\text{J},△H=+202.6\text{J}$
• C. $△U=-202.6\text{J},△H=-202.6\text{J}$
• D. $△U=0,△H=+202.6\text{J}$

Answer 1

The correct option is D $△U=0,△H=+202.6\text{J}$

$△H=\text{heat given. And the process is given to be isobaric}.$
Therefore
$△H=q=+202.6\text{J}$
And, $w=-P_{ext}\left(△V\right)=-1\times 2\text{litre. atm}\times 101.3=-202.6\text{J}$
Hence, $△U=q+w=0$