Question

Let C_v and C_p denote the molar heat capacities of an ideal gas at constant volume and constant pressure respectively. Which of the following is a universal constant?
(a) $\frac{C_p}{C_v}$
(b) C_pC_v
(c) C_p − C_v
(d) C_p + C_v

Answer 1

(c) C_p − C_v

For an ideal gas, C_p − C_v = R , where C_v and C_p denote the molar heat capacities of an ideal gas at constant volume and constant pressure, respectively and R is the gas constant whos value is 8.314 J/K. Therefore, C_p − C_v is a constant. On the other hand, the ratio of these two varies as the atomicity of the gas changes. Also, their sum and product are not constant.