Use Hess's Law to calculate the heat of reaction for the following reaction:

A + 3B → 3C + 2D

A + 2B → C + D H = - 20 kJ

B → 2C + D H = - 45 kJ

Question 10 options:

+25 kJ

-65 kJ

-25 kJ

+65 kJ

-65kJ

Explanation:

It is possible to calculate the heat of a reaction by the sum of half-reactions, thus:

(a) A + 2B → C + D ΔH = - 20 kJ

(b) B → 2C + D ΔH = - 45 kJ

The sum of (a) + (b) gives:

(a) + (b) A + 3B → 3C + 2D ΔH = - 20kJ - 45kJ = - 65kJ

Thus, heat of reaction is - 65kJ