JEE Advanced 2019 · Paper 1 · Chemistry Q8

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ChemistryMultiple correct+4 / -1Question 26 of 54

Which of the following statement(s) is(are) correct regarding the root mean square speed $(u_{rms})$ and average translational kinetic energy $(\varepsilon_{av})$ of a molecule in a gas at equilibrium?

u_{rms}

is doubled when its temperature is increased four times

\varepsilon_{av}

is doubled when its temperature is increased four times

\varepsilon_{av}

at a given temperature does not depend on its molecular mass

u_{rms}

is inversely proportional to the square root of its molecular mass

Answer and worked solution

Official answer: A, C, D

$u_{rms}=\sqrt{3RT/M}$ and $\varepsilon_{av}=\frac32k_BT$ .

(A) Four times the temperature doubles $u_{rms}$ . True.
(B) $\varepsilon_{av}$ is proportional to $T$ , so it becomes four times larger, not double. False.
(C) $\varepsilon_{av}$ depends only on $T$ , not on the molecular mass. True.
(D) $u_{rms}\propto M^{-1/2}$ . True.

(A), (C), (D)

Topics:Kinetic theory of gases

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