Q. A cylinder of fixed capacity (of 44.8 litres) contains 2 moles of helium gas at STP. What is the amount of heat needed to raise the temperature of the gas in the cylinder by $20℃$ (Use $R = 8.31\ J\ mol^{- 1}K^{- 1}$)
A) 996 J
B) 831 J
C) 498 J
D) 374 J
Explanation
(c) Since the volume of cylinder is fixed, the heat required is determined by $C_{V}$
$He$ is a monoatomic gas.
Therefore, its molar specific heat at constant volume is
$C_{V} = \frac{3}{2}R$
$\therefore$ Heat required = no. of moles $\times$ molar specific $\times$ rise in temperature
$= 2 \times \frac{3}{2}R \times 20 = 60R = 60 \times 8.31 = 498.6J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.