Question

Four mole of hydrogen two mole of helium and one mole of water vapour form an ideal gas mixture. What is the molar specific heat at constant pressure of mixtures?

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

Answer 1

Answer: (D)

$\frac{23}{7}R$

$C_V$ for hydrogen = $\frac{5}{2}R$
$C_v$ for helium = $\frac{3R}{2}$
$V_V$ for water vapour = $\frac{6R}{2}=3R$
$\therefore$ $(C_V{)}_{mix}$ = $\frac{4\times \frac{5}{2}R+2\times \frac{3}{2}R+1\times 3R}{4+2+1}$ = $\frac{16}{7}R$
$\therefore$ $C_P$ = $C_V+R$
$C_P$ = $\frac{16}{7}R+R$
Or, $C_P$ = $\frac{23}{7}R$