Enthalpy And Enthalpy Change
Category : JEE Main & Advanced
Heat content of a system at constant pressure is called enthalpy denoted by ‘H’.
From first law of thermodynamics, \[q=E+PV\] ……….(i)
Heat change at constant pressure can be given as
\[\Delta q=\Delta E+P\Delta V\] ……….(ii)
At constant pressure heat can be replaced at enthalpy.
\[\Delta H=\Delta E+P\Delta V\] ………(iii)
\[\therefore \,\Delta H=\] Heat change or heat of reaction (in chemical process) at constant pressure
\[\Delta E=\] Heat change or heat of reaction at constant volume.
In case of solids and liquids participating in a reaction,
\[\Delta H=\Delta E\,(P\Delta V\approx 0)\]
Difference between \[\Delta H\] and \[\Delta E\] is significant when gases are involved in chemical reaction.
\[\Delta H=\Delta E+P\Delta V\]
\[\Delta H=\Delta E+\Delta nRT\]
\[P\Delta V=\Delta nRT\]
Here, \[\Delta n=\] nP – nR
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