chem problem.2..?

Question

Given the following data:


2Mg + O2 → 2MgO DH = −1204


MgO + H2O → Mg(OH)2 DH = −37


2H2O → 2H2 + O2 DH = +572 kJ




Calculate DH for the reaction


Mg + H2 + O2 → Mg(OH)2

Answer 1

Add these equations:

reaction 1 DH = -1204
(2 x reaction 2) DH = -74
+ (reverse of reaction 3) DH = - 572

and you get

2 Mg + 2 H2 + 2 O2 --> 2 Mg(OH)2 DH = - 1850

so DH = -925 for the given reaction.