Question

PV versus T graph of equal masses of H₂, He and CO₂ is shown in figure. Choose the correct alternative

• A. 3 corresponds to H₂, 2 to He and 1 to CO₂
• B. 1 corresponds to He, 2 to H₂ and 3 to CO₂
• C. 1 corresponds to He, 3 to H₂ and 2 to CO₂
• D. 1 corresponds to CO₂, 2 to H₂ and 3 to He

Answer 1

Answer: (A)

3 corresponds to H₂, 2 to He and 1 to CO₂

Answer 2

For equal masses of gases, the number of moles $n$ is inversely proportional to the molar mass $M$, given by $n = \frac{m}{M}$.

• H₂ has the smallest molar mass ($M \approx 2$), so it has the largest number of moles.
• He has an intermediate molar mass ($M \approx 4$).
• CO₂ has the largest molar mass ($M \approx 44$), so it has the smallest number of moles.

In a PV vs. T graph, the slope is proportional to $nR$. Therefore, a higher $n$ results in a steeper slope.

• Line 3 (steepest) corresponds to H₂.
• Line 2 (intermediate) corresponds to He.
• Line 1 (shallowest) corresponds to CO₂.