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Explain the relation of change in heat at constant pressure and constant temperature. |
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Answer» SOLUTION :At CONSTANT TEMPERATURE thermal change `d_V = Delta U` At constant pressure thermal change `q_(p) = Delta U` At constant pressure `H Delta U + p Delta V` where, `Delta V=` Change in volume `V_1 = ` Initial volume `V_2=` Final volume `Delta H = Delta U + p(V_(2) + p(V_(2) - V_(1) ) = Delta U + (pV_(2)- pV_(1) ) ""...(i)` According to ideal gas equation `pV = nRT` `pV_(1) = n_(1) RT ""...(II)` `pV_(2) =n_(2)RT""...(iii)` Where, `n_1 =` Moles of gaseous reactions. `n_2=` Moles of gaseous products. Put the volume of eq. (ii) and (iii) into eq. (i) `Delta H = Delta U + (n_(2) RT - n_(1) RT) ` `therefore Delta U = Delta U + (n_(2) - n_(1) ) RT` `DeltaH= Delta U + Delta n_(g) RT` Where, `Deltan_(g)=` Difference between moles of gaseous product and gaseous reactants. If `Delta n_(g) =0` than `Delta H= Delta U` If `Delta n_(g) gt 0` than `Delta H gt Delta U` If `Delta n_(g) lt 0` than `DeltaH lt Delta U` |
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