Q.

When 300 J of heat is given to an ideal gas with Cp=72R its temperature raises from 20°C to 50°C keeping its volume constant. The mass of the gas is (approximately) _______ g.    (R=8.314  J/mol.K)                   [2026]


Ans.

(481)

For a constant volume process, the heat supplied (Q) is given by the formula:

Q=nCvΔT

Where:

1. n = number of moles of the gas.
2. Cv = molar specific heat capacity at constant volume.
3. ΔT = change in temperature =50°C-20°C=30°C=30K

We are given the molar specific heat at constant pressure, Cp=72R. Using Mayer's relation (Cp-Cv=R):

Cv=Cp-R

Cv=72R-R=52R

Using the formula of heat,

300=n×(52×8.314)×30

n=300×25×8.314×300.481 moles

So, the amount of the gas is 0.481 moles. As the molar mass of the gas is not given in the question, we can't determine the mass of the gas directly.