Question

(a) Is it possible to change the temperature and pressure of a fixed mass of a gas without changing its volume? Explain your answer.
(b) Define or explain the meaning of the term 'molar volume'.

Answer 1

(a) It is given that mass of a gas is fixed; i.e., the number of moles of gas does not change.
According to the ideal gas equation:
PV = nRT
$\frac{P}{T}=\frac{n\mathrm{R}}{V}$
Let us suppose that the initial pressure, temperature and volume of the gas were P₁, T₁ and V₁.
$\frac{P_1}{T_1}=\frac{\mathrm{n}\mathrm{R}}{V_1}$
Let the final pressure, temperature and volume of the gas be P₂, T₂ and V₂.
$\frac{P_2}{T_2}=\frac{\mathrm{n}\mathrm{R}}{V_2}$
As P₍₁₎/T₍₁₎ is not equal to P₍₂₎/T_(2). Hence, volume of gas must be changed as n and R are constant. Therefore, it is not possible to change the temperature and pressure of a fixed mass of a gas without changing its volume.

(b) Molar volume is the volume occupied by one mole of any gaseous substance at standard temperature and pressure. This molar volume has fixed value for any gaseous molecule, which is 22.4 L or 22,400 mL.