Consider the reaction
Mg(OH)2(s) → MgO(s) + H2O(l)
with enthalpy of reaction ΔH°rxn = 37.5 kJ/mol. What is the enthalpy of formation of MgO(s)?
Express your answer in kilojoules per mole to one decimal place.
Enthalpy ΔH is a measure of the energy content of a system at constant pressure. Chemical reactions involve changes in enthalpy, ΔH, which can be measured and calculated:
ΔH°rxn = ΣmΔH°f, products − ΣnΔH°f, reactants
where the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation" and mm and n represent the appropriate stoichiometric coefficients for each substance.
The following table lists some enthalpy of formation values for selected substances.
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