Question

Four moles of hydrogen, $2moles$ of $He$ and $1mole$ of water vapour form an ideal gas mixture. What is the molar specific heat at constant pressure of mixture?

• A. $\frac{16}{7}R$
• B. $\frac{7R}{16}$
• C. $R$
• D. $\frac{23}{7}R$

Answer 1

The correct option is D $\frac{23}{7}R$

Average degree of freedom of the mixture=$\frac{\left(4\right)\left(5\right)+\left(2\right)\left(3\right)+\left(1\right)\left(6\right)}{4+2+1}=\frac{32}{7}$

Hence $C_V=\frac{f}{2}R=\frac{16}{7}R$

$⟹C_P=C_V+R=\frac{23}{7}R$