The internal energy change in a system that has absorbed $2 \mathrm{kcal}$ of heat and done $500…
The internal energy change in a system that has absorbed $2 \mathrm{kcal}$ of heat and done $500 \mathrm{~J}$ of work is
$8900 \mathrm{~J}$
$6400 \mathrm{~J}$
$5400 \mathrm{~J}$
$7900 \mathrm{~J}$
Solution
Key Idea Heat given to a system ( $\Delta Q$ ) is equal to the sum of increase in the internal energy $(\Delta \mathrm{u})$ and the work done $(\Delta W)$ by the system against the surrounding and $1 \mathrm{cal}=4.2 \mathrm{~J}$.
According to first law of thermodynamics
$\begin{aligned}
\Delta \mathrm{U} & =\mathrm{Q}-\mathrm{W} \\
& =2 \times 4.2 \times 1000-500 \\
& =8400-500 \\
& =7900 \mathrm{~J}
\end{aligned}$