Question

Find the change in internal energy of the system when a system absorbs $2kcal$ of heat and at the same time does $500J$ of work

• A. $8200J$
• B. $7900J$
• C. $6400J$
• D. $5600J$

Answer 1

The correct option is B $7900J$

Heat absorbed is $dQ=2000cal=200\times 4.18=8368J$ and the work done is $dW=500J$.

Using first law, we have $dQ-dW=dU=8368-500=7868\approx 7900J$