Question

The density of a polyatomic gas in standard conditions is $0.795kg/m^3$. The specific heat of the gas at constant volume is

• A. $930J/kgK$
• B. $1400J/kgK$
• C. $1120J/kgK$
• D. $1600J/kgK$

Answer 1

The correct option is B $1400J/kgK$

For given polyatomic gas, applying ideal gas equation PM=dRT under standard conditions, where P=pressure=1atm, M=molar mass, d=density=$0.795kg/m^3$,

R=universal gas constant,

T=absolute temperature=$273K$

M=$0.795\times 8.31\times \frac{273}{100000}=0.018kg=18g$
Hence, molecule is $H_{2}O\Rightarrow$ degree of freedom =6
$\Rightarrow$ specific heat at constant volume=$C_v=\frac{f}{2}R=3R=3\times 8.31\times \frac{1000}{18}=1400J/kgK$