Question

Three moles of oxygen are mixed with two moles helium. What will be the ratio of specific heats at constant pressure and constant volume for the mixture ?

• A. 2.5
• B. 3.5
• C. 1.5
• D. 1

Answer 1

Answer: (C)

1.5

Answer 2

For a monoatomic gas like helium $\gamma_{He} = \frac{5}{3}$

For a diatomic gas like oxygen $\gamma_{O_{2}} = \frac{7}{5}$

$\therefore\gamma_{mix} = \frac{3 \times \gamma_{O_{2}} + 2 \times \gamma_{Ηe}}{(3 + 2)}$

$= \frac{3 \times \frac{7}{5}2 \times \frac{5}{2}}{5} = \frac{\frac{21}{5} + \frac{10}{3}}{5} = \frac{113}{15 \times 5} = 1.5$