Calculate the delta H for Y + XZ = XY + Z

Question

Given the following data:

X + Y = XY delta H= a kJ

X + Z = XZ delta H= b kJ

Answer 1

Hess' Law:

Y + XZ ==> XY + Z TARGET EQUATION

Given:

(1). X + Y = XY ∆H = a kJ

(2). X + Z = XZ ∆H = b kJ

Procedure:

copy (1) to get Y on the left: X + Y = XY ∆H = a kJ

reverse (2) to get XZ on the left: XZ = X + Z ∆H = -b kJ (note: change the sign of ∆H)

Add these together to get ...

X + Y + XZ = XY + X + Z and cancel like terms to get

Y + XZ = XY + Z TARGET EQUATION

∆H for target equation = a kJ - b kJ