Question

Find the external work done by the system inkcal, when 20 keal of heat is supplied to thesystem and the increase in the internal energyis 8400$J(J=4200J/kcal)?$

• A. 16$kcal$
• B. 18$kcal$
• C. 20$kcal$
• D. 19$kcal$

Answer 1

The correct option is B 18$kcal$

According to $1st$ law of thermodynamics
$dU=q+W$
$8.4kJ=(20\times 4.2kJ)+W$
$W=8.4kJ-84kJ$
$W=-75.6kJ$
$W=-75.6/4.2=-18$ $kcal$
Work done by system is $18$ $kcal$

Hence,

option $\left(B\right)$ is correct answer.