Hess's Law Answers

1. -1220 kJ

2. Here's what will happen:
Multiply (1) by 2, Leave (2) as it is, reverse (3).

Heat of Reaction= 15.3 kJ

3. This is wicked hard. If  you do this I'll give you extra credit. For better practice, try this,


(1)  Find the ΔH for the reaction below, given the following reactions and subsequent ΔH values:
PCl₅(g)  →  PCl₃(g)  +  Cl₂(g)

P₄(s)  +  6Cl₂(g)  →  4PCl₃(g)            ΔH = -2439 kJ

4PCl₅(g)  →  P₄(s)  +  10Cl ₂(g)         ΔH = 3438 kJ
answer = 249.8 kJ