A mixture contains $2 mol$ of helium and $3 mol$ of hydrogen (rigid diatomic). Treating both as ideal, the ratio $C_{P} / C_{V}$ of the mixture is nearest to

Answer: C

Mixture

C_{V} = (2 \times 1.5 R + 3 \times 2.5 R) /5 = 2.1 R

per mole, so

C_{P} = C_{V} + R = 3.1 R

. Hence

γ = 3.1/2.1 = 1.476

, about 1.48. The simple average of the two

γ

values is wrong because heat capacities, not ratios, add.