Question

Two flasks A and B of equal volume, maintained at 300 K and 700 K contain equal masses of helium and nitrogen gases respectively. What is the ratio of transitional kinetic energy of the gas in flask A to that of flask B?

• A. 1 : 3
• B. 3 : 1
• C. 3 : 49
• D. None of these

Answer 1

The correct option is B 3 : 1

Say, $w_{He}=w_{N_2}=w$
Then, ${}^{n}He=\frac{w}{4};{}^n{N}_2=\frac{w}{28}$
$\frac{KE}{mole}=\frac{3}{2}RT$
$\therefore K{E}_{He}=\frac{3}{2}\times R\times 300\times \frac{w}{4}=\frac{900Rw}{8}$
${KE}_{N_2}=\frac{3}{2}\times R\times 700\times \frac{w}{28}=\frac{300Rw}{8}$
$\therefore \text{ratio}=\frac{900Rw}{8}:\frac{300Rw}{8}=3:1$