STANDARD HEAT OF FORMATION. DEFINITION The change in enthalpy that accompanies the formation of one mole of the compound at its normal state from its.

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Presentation transcript:

STANDARD HEAT OF FORMATION

DEFINITION The change in enthalpy that accompanies the formation of one mole of the compound at its normal state from its constituent elements in their standard state. Standard state is 1atm & 25°C (298K) Every free element in its standard state is assigned a ΔH f of 0.0 kJ. Free elements include single elements and any diatomic molecule (H 2 O 2 N 2 Cl 2 Br 2 I 2 F 2 )

EQUATION ΔH rxn = ΣΔH ƒ (product) − ΣΔH ƒ (reactants) ° ° **Σ is the Greek letter sigma. It means sum, or add. We are finding the sum (Σ) of the change in heat of formation (ΔH f ) of the reactants and subtracting it from the sum of the change in heat of formation of the products.

reactants products

**look up ΔH f values in the table provided reactantsproducts

reactantsproducts

reactants products