Question

A system is provided with $200\text{cal}$ of heat and the work done by the system on the surrounding is $40\text{J}$. Calculate the change in internal energy of the system?

• A. Increases by $600\text{J}$
• B. Decreases by $800\text{J}$
• C. Increases by $800\text{J}$
• D. Increases by $160\text{J}$

Answer 1

The correct option is C Increases by $800\text{J}$

From the first law of thermodynamic, $\Delta U=q+W$
$q=200\text{cal}=200\times 4.2=840\text{J}$
$W=-40\text{J}\text{(Because work is done by the system on the surrounding)}$
$\Delta U=q+w=840-40=800\text{J}$