Question

Two moles of oxygen is mixed with eight moles of helium. The effective specific heat of the mixture at constant volume is:

• A. 1.3R
• B. 1.4R
• C. 1.7R
• D. 1.9R

Answer 1

Answer: (C)

1.7R

For mixture of gases, let specific heat be $C_1$

$C_V=\frac{n_1(C_V{)}_1+n_2(C_V{)}_2}{n_1+n_2}$

where,

Oxygen being a diatomic gas, it has $(C_V{)}_1=\frac{5R}{2}$

Helium is a monoatomic gas. So, it has $(C_V{)}_2=\frac{3R}{2}$

$C_V=\frac{2\times \frac{5R}{2}+8\times \frac{3R}{2}}{2+8}=\frac{17R}{10}=1.7R$