NEET UG CHEMISTRY MCQ: THERMODYNAMICS

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The standard heat of combustion of solid boron is :

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Correct option: D

- \frac{1}{2}{\Delta _f}\Delta H^\circ \left( {{\mathrm{B}_2}{\mathrm{O}_3}} \right)

Option D (

- \frac{1}{2}{\Delta _f}\Delta H^\circ \left( {{\mathrm{B}_2}{\mathrm{O}_3}} \right)

) is correct because the standard heat of combustion of solid boron is related to the formation of B2O3, considering the stoichiometry of the reaction.

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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