Consider the reaction with enthalpy of reaction Na2CO3(s)Na2O(s)+CO2(g) What is the enthalpy of formation of Na2O(s) ? Hrxn=321.5kJ/mol Express your answer in kilojoules per mole to one decimal place system at constant pressure. Chemical reactions involve changes in enthalpy, H, which can be measured and calculated: Hrxn=productsmHfreactantsnHf where the subscript "rxn" is for "enthalpy of reaction" and " f " is for "enthalpy of formation" and m and n represent the appropriate stoichiometric coefficients for each substance. The following table lists some enthalpy of formation values for selected substances