The heat of formation $\mathrm{H}_2 \mathrm{O}({l})$ is $-68.0 \mathrm{~kcal},$ the heat of formation of $\mathrm{H}_2 \mathrm{O}(\mathrm{g})$ is likely to be

NEET UG CHEMISTRY MCQ: THERMODYNAMICS

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The heat of formation

\mathrm{H}_2 \mathrm{O}({l})

-68.0 \mathrm{~kcal},

the heat of formation of

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

is likely to be

View answer and explanation

Correct option: A

-68.0 \mathrm{~kcal}

Option D is the closest. The heat of formation of H2O(g) will be less negative than H2O(l) because energy is required to vaporize the liquid into gas. Therefore, the heat of formation of H2O(g) will be closer to zero than -68.0 kcal, making -58.3 kcal the most reasonable answer.

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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