Wednesday, May 18, 2011

Relation Between ΔH AND ΔE


When a system changes from initial to final state,
                            DH  =  H2    H1
            Where H2 and H1 are enthalpies of final and initial state respectively.
                            But,   H      =      E  +  PV.
                            DH    =     (E2 + P2V2) – (E1 + P1V1)
                            DH    =     E2 + P2V2 – E1 – P1V1
                            DH    =     E2 – E1 + P2V2 – P1V1                         
                            DH    =     DE  +  P2V2 – P1V1 
                            But,   PV     =     nRT.
                            \                  P1V­1  =     n1RT
                            &                   P2V2  =     n2RT, at constant temperature.
                                                  DH     =    DE   +   n2RT – n1RT
                                                  DH     =    DE   +   RT (n2 – n1)   
                                                  DH     =    DE   +   DnRT                                                  
                            Where n2 – n1 is change in moles.

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