II2( g)+(1)/(2) O2( g) →II2 O(1) ; ΔH29 ×K=68.32 kcal . Heat of vapourisation of water at I atm

step 1 1 molecule of hydrogen gas reacts with half molecule of oxygen forming 1 molecule of water. Enth

II2( g)+(1)/(2) O2( g) →II2 O(1) ; ΔH29 ×K=68.32 kcal . Heat...

$\mathrm{II}_{2}(\mathrm{~g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{II}_{2} \mathrm{O}(1) ; \Delta H_{29 \times \mathrm{K}}=68.32 \mathrm{kcal} .$ Heat of vapourisation of water at I atm and $25^{\circ} \mathrm{C}$ is $10.52$ kcal. The standard heat of formation (in kcal) of 1 mole of water vapour at $25^{\circ} \mathrm{C}$ is (1) $-78.84$ (2) $78.84$ (3) $+57.8$ (4) $-57.8$

$\mathrm{II}_{2}(\mathrm{~g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{II}_{2} \mathrm{O}(1) ; \Delta H_{29 \times \mathrm{K}}=68.32 \mathrm{kcal} .$
Heat of vapourisation of water at I atm and $25^{\circ} \mathrm{C}$ is $10.52$ kcal. The standard heat of formation (in kcal) of 1 mole of water vapour at $25^{\circ} \mathrm{C}$ is
(1) $-78.84$
(2) $78.84$
(3) $+57.8$
(4) $-57.8$

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Key Concepts

Heat of Vaporisation

The heat of vaporisation is the amount of energy required to vaporize one mole of a liquid at a given temperature and pressure. It is key in processes involving phase transitions, and when combined with other reaction enthalpies, it allows the determination of the thermodynamics for processes occurring over different phases.

Standard Enthalpy of Formation

This is the enthalpy change accompanying the formation of one mole of a compound from its constituent elements in their standard states. It is a fundamental thermodynamic quantity used to assess the stability of compounds and to calculate reaction energies using tabulated formation values.

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is independent of the path taken, as enthalpy is a state function. This allows the calculation of an overall reaction enthalpy by breaking a multistep process into simpler steps with known enthalpy changes and then summing these changes.

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