NEET UG CHEMISTRY MCQ: THERMODYNAMICS

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Analyzing +4 | -1

The data below refers to gas phase reaction at constant pressure at

25^{\circ} \mathrm{C}.

\begin{aligned} & \text{(a) } \mathrm{CH}_3-\mathrm{CH}_3 \rightarrow \mathrm{CH}_3-\mathrm{CH}_2+\mathrm{H}; \Delta H_1=+420 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \text{(b) } \mathrm{CH}_3-\mathrm{CH}_2 \rightarrow \mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}; \Delta H_2=+168 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}

From these data, the enthalpy change

\Delta H

for the reaction

2 \mathrm{CH}_3-\mathrm{CH}_2 \rightarrow \mathrm{CH}_3-\mathrm{CH}_3+\mathrm{CH}_2=\mathrm{CH}_2

View answer and explanation

Correct option: C

-252 \mathrm{~kJ}

Option C (-252 kJ) is correct because the enthalpy change for the overall reaction can be found by reversing reaction (a) and adding it to reaction (b), then summing the enthalpy changes.

More Questions from THERMODYNAMICS

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The internal energy of one mole of a gas is: An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If

{T_i}

is the initial temperature and

{T_f}

is the final temperature, which of the following statements is correct? For which of the process, ∆S is negative? The work done by a weightless piston in causing an expansion ∆V (at constant temperature), when the opposing pressure, P is variable, is given by: Assertion :- At constant pressure of the change

\mathrm{H}_2 \mathrm{O}(\mathrm{s}) \rightarrow \mathrm{H}_2 \mathrm{O}(\mathrm{g})

work done is negative.

Reason :- During phase transition work done is always negative. For the reaction,

\mathrm{X}_2 \mathrm{O_4(l}) \longrightarrow 2 \mathrm{XO}_2(\mathrm{g}), \Delta U=2.1 \mathrm{~kcal}, \Delta S=20 \mathrm{~cal} \mathrm{~K}^{-1}

300 \mathrm{~K}

. Hence,

\Delta G