Question

A gas mixture consists of 2 moles of oxygen and 4 moles of argon at temperature T. Neglecting all vibrational modes, the total internal energy of the system is?

(a) 4RT

(b) 9RT

(c) 11RT

(d) 15RT

I got this question in my homework.

This key question is from Gases topic in chapter Kinetic Theory of Gases of Engineering Physics I

Answer 1

Correct choice is (c) 11RT

Easiest explanation: For two moles of diatomic nitrogen with no vibrational mode,

U1=2×5/2 RT=5RT

For four moles of monoatomic argon,

U2=4×3/2 RT=6RT

Therefore, U=U1+U2=11RT.