Explain : Enthalpy : state function.ORDelta H= q_(p) Or Prove : "The change in enthalpy of the system in which chemical reaction occurs is equal to value of heat gain by system."

Explain : Enthalpy : state function.ORDelta H= q_(p) Or Prove : "The c

1.	Explain : Enthalpy : state function.ORDelta H= q_(p) Or Prove : "The change in enthalpy of the system in which chemical reaction occurs is equal to value of heat gain by system."
Answer» SOLUTION :`Delta U= q+w` we may WRITE as `Delta U = q_(p) - pDelta V` at constant pressure, where `q_(p)=` heat absorbed by system `pDelta V=` expansion work done by system When heat is absorbed at constant pressure by system, internal energy turns form `U_(1)` to `U_(2)` and volume turns `V_(1)` to` V_(2)`. `therefore Delta U= U_(2) - U_(1)` `Delta V= V_(2) - V_(1)` Put this value in above equation. `therefore U_(2) - U_(1) = q_(p) - p (V_(2) - V_(1) )` `q_(p) = (U_(2) - U_(1) ) + P (V_(2) - V_(1) )` `q_p = (U_(2) + pV_(2)) - (U_(1) + pV_(1) ) ""...(i)` here, `U+pV` is a state function. It is mentioned as H `H= U+ pV""...(ii)` `therefore q_(p) = H_(2) - H_(1) = Delta H` H is a state function, because, U, p, V are state functions, for fixed change at constant pressure, `Delta H = Delta U + pDelta V ""...(iii)` `Delta H` is positive for endothermic reactions which ABSORB heat from the surroundings and `Delta H` is NEGATIVE for exothermic reactions which evolve heat during the reaction.