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  4. A cylinder of fixed capacity (ot 44.8 L) 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° C ? (Use R = 8.31 Jmol-1K-1)

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Q. A cylinder of fixed capacity (ot 44.8 L) 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 $20^\circ C$ ? (Use R = 8.31 Jmol$^{-1}K^{-1})$

Thermodynamics

Solution:

Since, the volume of cylinder is fixed and helium is a monoatomic gas.
The internal energy $=\mu C_v\Delta T$
$U=\frac{1}{2}f \mu R\Delta T$ $\left[\therefore C_v=\frac{1}{2}f R\right]$
$U=\frac{1}{2}\times3\times8.32\times20.$
= 498.6 J