Question

What is the difference in heat capacities at constant volume and pressure?

(a) Universal volume constant

(b) Universal gas constant

(c) Universal pressure constant

(d) Universal temperature constant

I had been asked this question during a job interview.

My question comes from Thermodynamics Applications topic in chapter Thermodynamics of Chemistry – Class 11

Answer 1

Correct option is (b) Universal gas constant

To elaborate: We all know that ΔH = ΔU + nRΔT; ΔH = nCPΔT and ΔU = nCvΔT; ΔH – ΔU = nCPΔT – nCvΔT = n(CP – CV) ΔT. By equating L.H.S. and R.H.S., we get n(CP – CV) ΔT = nRΔT; CP – CV = R. Hence it’s proven that difference of heat capacities at constant volume and pressure is the universal gas constant.