Enthalpy of Formation Video Lessons

Concept:

# Problem: Consider the reactionMg(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, reactantswhere 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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###### Problem Details

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)?

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.