Because the molecules of a liquid room in constant motion and possess a wide selection of kinetic energies, at any kind of moment some portion of them has actually enough power to escape from the surface of the liquid to go into the gas or vapor phase. This process, dubbed vaporization or evaporation, generates a vapor pressure above the liquid. The warm of Vaporization (also called the Enthalpy that Vaporization) is the heat compelled to induce this phase change.

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Figure \(\PageIndex1\): heat imparts power into the mechanism to overcome the intermolecular interaction that organize the liquid with each other to generate vapor.

Since vaporization requires warm to be added to the system and hence is one endothermic process, as such \( \Delta H_vap > 0\) together defined:

\< \Delta H_vap = H_vapor - H_liquid\>

where

\( \Delta H_vap\) is the change in enthalpy the vaporization \(H_vapor\) is the enthalpy the the gas state the a link or facet \(H_liquid\) is the enthalpy of the liquid state of a link or element

Heat is absorbed when a liquid boils because molecules i beg your pardon are held together by intermolecular attractive interactions and also are jostled free of each various other as the gas is formed. Together a separation requires power (in the kind of heat). In basic the power needed different from one fluid to an additional depending on the magnitude of the intermolecular forces. We can thus suppose liquids with solid intermolecular pressures to have actually larger enthalpies that vaporization. The list of enthalpies that vaporization offered in the Table T5 bears this out.




The Enthalpy of Condensation

Condensation is the opposite of vaporization, and therefore \( \Delta H_condensation\) is likewise the opposite of \( \Delta H_vap\). Due to the fact that \( \Delta H_vap\) is an endothermic process, where heat is lost in a reaction and must be added into the mechanism from the surroundings, \( \Delta H_condensation\) is one exothermic process, where warmth is took in in a reaction and must be offered off indigenous the system into the surroundings.

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\<\beginalign ΔH_condensation &= H_liquid - H_vapor \\<4pt> &= -ΔH_vap \endalign\>

Because \(ΔH_condensation\), also written together \(ΔH_cond\), is an exothermic process, its value is constantly negative. Moreover, \(ΔH_cond\) is same in size to \(ΔH_vap\), so the just difference between the 2 values for one offered compound or element is the hopeful or negative sign.






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