# Find the standard enthalpy of formation of ethylene, C2H4(g), given the following data: C2H4(g) + 3O2(g)  -->  2CO2(g) + 2H2O(l)     H°rxn  = –1411 kJ Given that: H°f[CO2(g)] = –393.5 kJ/mol H°f[H2O(l)] = –285.8 kJ/mol

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The heat of reaction is the result of the breaking of bonds within the reactant species and the reforming of bonds to make the product species. The heat of formation (`Delta` H°f) is the energy required to form a compound in kilojoules per mole of substance. Heats of formation can be used to calculate the heat of reaction (`Delta` H°rxn) by subtracting the heats of formation of the reactants from the heats of formation of the products:

Heat of reaction = Heats of formation of products - Heats of formation of reactants

Heats of formation can be found in tables such as the one found here . Elements have a heat of formation of zero (they are the building...

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