2001 AIPMT ThermodynamicsFirst law of thermodynamics Easy Question 4 of 4 in First law of thermodynamics

When 1 mol gas is heated at constant volume temp. is raised from 298 to 308 K. Heat supplied to the gas is 500 J. Then which statement is correct : -

A q = w = 500 J, $\Delta U$ = 0
B q = $\Delta U$ = 500 J, w = 0
C q = –w = 500 J, $\Delta U$ = 0
D $\Delta U$ = 0, q = w = –500 J

The answer is B.

Solution

At constant volume, no expansion work is done: $w = -P\Delta V = 0$.
First law: $\Delta U = q + w = q + 0$
So all the heat supplied increases the internal energy: $q = \Delta U = 500$ J and w = 0.
($\Delta U$ cannot be zero, since the temperature rises.)

Concept Heat at constant volume

First law of thermodynamics in past papers

4 questions from this chapter have appeared across 4 exam years.