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Define heat of formation.How is it usefu...

Define heat of formation.How is it useful in the calculation of the heat of a reaction ?

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The heat of formation or enthalpy of formation is the change in enthalpy of the system when one mole of a substance is formed directly from its elements. It is represented by `Delta_(f)H`
For example, `Fe(s) + S(s) rarr FeS(s), Delta_(f)H= -100.5kJ`. The heat of formation or enthalpy of formation is useful in the calculation of the heat of a reaction. It is given by below equation, Standard heat of reaction= [Sum of the standard heat of formation of products] - [Sum of the standard heat of formation of reactants]
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