Question

The molar heat capacity for an ideal gas at constant pressure is 20.785 J K-1 mol-1. The change in internal energy is 5000 J upon heating it from 300 K to 500 K. The number of moles of the gas at constant volume is _____. (Nearest integer)
(Given : R = 8.314 JK-1mol-1).

Answer 1

Cp = 20.785 JK-1 mol-1 and ΔU = nCvΔT
∴ nCv = $\frac{5000}{200}$ = 25
and we know that
Cp – Cv = R
20.785$-\frac{25}{n}$= 8.314
n = $\frac{25}{(20.785-8.314)}$
= 2