NEET UG CHEMISTRY MCQ: THERMODYNAMICS

1 Medium

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Analyzing +4 | -1

Consider the following reaction occurring in an automobile

2 {C}_8 {H}_{18}({~g})+25 {O}_2({~g}) \longrightarrow 16 {CO}_2({~g})+18 {H}_2 {O}({g})

the sign of

\Delta {H}, \Delta {S}

and

\Delta {G}

would be

View answer and explanation

Correct option: B

-,+,-

Option B (-,+,-) is correct because combustion reactions are exothermic (negative Δ H), increase disorder (positive Δ S), and are spontaneous (negative Δ G).

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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