J.R. S. answered • 06/11/18

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This is an example of Hess' Law

The target equation is 2NiCl

_{2}(s) + O_{2}(g) ==> 2NiO(s) + 2Cl_{2}(g)Eq (1) has 2NiO on the right as does the target, so simply copy it down...

2Ni(s) + O2(g) ==> 2NiO(s) ... ∆H = -479.4 kJ

Eq (2) Has NiCl2 on the right, but target has it on the left and w of them, so reverse it and x2 to get ...

2NiCl2(s) ==> 2Ni(s) + 2Cl2(g) ... ∆H = 2x+305.3 kJ (note change in sign when you reverse the rx) = +610.6 kJ

Add them together to get....

2Ni(s) + O2(g) + 2NiCl2(s) ===> 2NiO(s) + 2Ni(s) +2Cl2(g). Cancel appropriate species on each side to get...

2NiCl2(s) + O2 ===> 2NiO(s) + 2Cl2(g) This is the target equation.

Now, add the ∆H values : -479.4 kJ + 610.6 kJ = 131.2 kJ