The normal boiling point and $\Delta {H}_{\text {vap }}$ of a liquid ' ${X}$ ' are $400 {~K}$ and $40 {~kJ} {~mol}^{-1}$ respectively. Assuming $\Delta {H}_{\text {vap }}$ to be constant, which of the following is correct? (I) $\Delta {S}_{\text {vap }}>100 {JK}^{-1} {~mol}^{-1}$ at $400 {~K}$ and $0.5 {~atm}$ (II) $\Delta {S}_{\text {vap }} < 100 {JK}^{-1} {~mol}^{-1}$ at $400 {~K}$ and $1 {~atm}$ (III) $\Delta {S}_{\text {vap }} < 100 {JK}^{-1} {~mol}^{-1}$ at $400 {~K}$ and $2 {~atm}$ (IV) $\Delta {S}_{\text {vap }}=100 {JK}^{-1} {~mol}^{-1}$ at $400 {~K}$ and $1 {~atm}$

NEET UG CHEMISTRY MCQ: THERMODYNAMICS

1 Medium

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Analyzing +4 | -1

The normal boiling point and

\Delta {H}_{\text {vap }}

of a liquid '

{X}

' are

400 {~K}

and

40 {~kJ} {~mol}^{-1}

respectively. Assuming

\Delta {H}_{\text {vap }}

to be constant, which of the following is correct?
(I)

\Delta {S}_{\text {vap }}>100 {JK}^{-1} {~mol}^{-1}

400 {~K}

and

0.5 {~atm}

(II)

\Delta {S}_{\text {vap }} < 100 {JK}^{-1} {~mol}^{-1}

400 {~K}

and

1 {~atm}

(III)

\Delta {S}_{\text {vap }} < 100 {JK}^{-1} {~mol}^{-1}

400 {~K}

and

2 {~atm}

(IV)

\Delta {S}_{\text {vap }}=100 {JK}^{-1} {~mol}^{-1}

400 {~K}

and

1 {~atm}

View answer and explanation

Correct option: D

I, III and IV

Option D (I, III and IV) is correct. At the normal boiling point and 1 atm, ΔSvap = ΔHvap/T = 100 J/Kmol. Increasing pressure decreases ΔSvap.