JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Chemical Thermodynamics

A system does 200 J of work and at the same time absorbs 150 J of heat. The magnitude of the change in internal energy is ______ J. (Nearest integer)

Answer: 50

Solution

Write the first law as

Δ U = q + w

, with heat absorbed by the system counted positive and work done by the system counted negative. Here

q = + 150

J and

w = - 200

J, so

Δ U = 150 - 200 = - 50 J

The internal energy falls, and the magnitude of the change in internal energy is 50 J.

JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Integer answer