Question

A cylinder of fixed capacity $67.2$ liters contains helium gas at STP. Calculate the amount of heat required to raise the temperature of the gas by ${15}^{o}C$. ($R=8.314Jmo{l}^{-1}{k}^{-1}$)

• A. $520J$
• B. $560.J$
• C. $620J$
• D. $621.2J$

Answer 1

Answer: (B)

$560.J$

Since, the process is at constant volume,
Q = U as W = 0
Thus, Q = $n{C}_v\Delta T$
At STP, n = $\frac{PV}{RT}$
Since, He is diatomic, $C_v=2.5R$
Q = $\frac{PV}{RT}\times 2.5R\times 15$
Substituting the pressure and temperature values at STP,
P = 1 atm
V = 67.2 L
T = 298 K
we get,
Q = 560.9 J