Enthalpy H is a measure of the energy content of a system at constant pressure.

Question

Enthalpy H is a measure of the energy content of a system at constant pressure. Chemical reactions involve changes in enthalpy DeltaH, which can be measured and calculated: Delta {H_{ m rxn}}^circ = sum_{ m products} m Delta {H_{ m f}}^{circ} - sum_{ m reactants} n Delta {H_{ m f}}^{circ} where the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation." Enthalpy of formation for selected substances { m CO_2} (g) m Delta {H_{f}}^circ =-393~kJ/mol { m Ca(OH)_2}(s) m Delta {H_{f}}^circ =-987~kJ/mol { m H_2O} (l) m Delta {H_{f}}^circ =-286~kJ/mol { m CaCO_3}(s) m Delta {H_{f}}^circ =-1207~kJ/mol Consider the reaction { m Ca(OH)}_2, (s) ightarrow { m CaO}, (s) +{ m H_2O}, (l) with enthalpy of reaction Delta {H_{ m rxn}}^{circ} =65~ m kJ/mol What is the enthalpy of formation of { m CaO}, (s)?

Explanation / Answer

-636 KJ/mol

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