Consider the following three reactions:

Question

Ca(s) + 2H2O(l) ---> Ca2+(aq) + 2OH^- (aq) + H2(g)

CaO(s) + H2O(l) ---> Ca2+ (aq) + 2OH^- (aq)

H2(g) + 1/2O2 (g) ----> H2O (l)

Delta H = 430.75 kJ
Delta H = 81.55 kJ
Delta H = 285.63 kJ

Determine Delta H for the overall reaction:
Ca(s) + 1/2O2 (g) ---> CaO(s)

Answer 1

Add eqn 1 to eqn 3 to the reverse of eqn 2. Add the dH values; when you reverse the rxn change the sign of dH for that rxn.
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