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

Question

A + 3B —> 3C + 2D

A + 28 —> C+ D H= -20 kJ

B —> 2C+ D H= -45 kJ

(ANSWER CHOICE )

a. -65 kJ

b. +65 kJ

c. -25 kJ

d. +25 kJ

Answer 1

A + 3B ==> 3C + 2D TARGET EQUATION

A + 2B ==> C + D H = -20 kJ

B ===> 2C + D H = -45 kJ

Add them together to get ...

A + 3B ==> 3C + 2D and adding the ∆H values we have -20 + -45 = - 65 kJ

Answer would be (a) -65 kJ