Question

A system is provided with 200 cal of heat and the work done by the system on the surrounding is 40 J. Then its internal energy

• A. Increases by 600 J
• B. Decreases by 800 J
• C. Increases by 800 J
• D. Decreases by 50 J

Answer 1

Answer: (C)

Increases by 800 J

Answer 2

$\Delta Q = \Delta U + \Delta W$

$\because\Delta Q = 200cal = 200 \times 4.2 = 840J$and $\Delta W = 40J$

⇒$\Delta U = \Delta Q - \Delta W = 840 - 40 = 800J$