Calculate the enthalpy for the reaction D + F = G + H using G + C = A + B deltaH = 277
C + F = A delta H = 303
D = B + H delta H = -158

The enthalpy for the reaction : ΔH = -132

Given

Reaction and the enthalpy

Required

the enthalpy

Solution

Hess Law

Reaction 1 reverse :

A + B = G + C  ΔH = -277

Reactions 2 and 3 remain the same (unchanged)

C + F = A         ΔH = 303

D = B + H         ΔH = -158

Add up all the reactions and remove the same compound from two different sides

D + F = G + H  ΔH = -132

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