Consider this combination reaction:
2mg(s)+o2(g)→2mgo(s) δh=−1204 kj
what is the enthalpy for the decomposition of 1 mole of mgo(s) into mg(s) and o2(g)?

Since the decomposition of MgO is the reverse of the reaction you have given us. The sign will be reversed:

2MgO -> 2Mg + O2 =  1204 kJ

Divide by two:

MgO -> Mg + 1/2 O2 =

602 kJ

Ibelieve it's celsius. hope this .

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