Question

The change in the energy of the system if 500 cal of heat energy are added to a system and the system does 350 cal of work on the surroundings will be:

• A. +150 cal
• B. -150 cal
• C. +350 cal
• D. -850 cal

Hint:

The change in internal energy is the heat added minus the work done by the system.

Answer 1

The Correct Option is B

According to the first law of thermodynamics: \[ \Delta U = Q - W \] where: - \(\Delta U\) is the change in internal energy,
- \(Q\) is the heat added to the system, and
- \(W\) is the work done by the system on the surroundings. Here, \(Q = 500 \, \text{cal}\) and \(W = 350 \, \text{cal}\). Thus: \[ \Delta U = 500 - 350 = 150 \, \text{cal} \] Since the work is done on the surroundings, the change in internal energy is -150 cal. Thus, the correct answer is Option (B).