The heat of formation is the change in enthal | vedclass

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(C) The enthalpy of formation $(\Delta H_f)$ is defined as the change in enthalpy when $1 \ mole$ of a substance is formed from its constituent elemen

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May be negative or positive

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(C) The enthalpy of formation $(\Delta H_f)$ is defined as the change in enthalpy when $1 \ mole$ of a substance is formed from its constituent elements in their standard states.Since the enthalpy of elements in their standard state is defined as zero,the enthalpy of formation of a compound depends on the energy released or absorbed during the bond formation process.Exothermic reactions result in a negative $\Delta H_f$,while endothermic reactions result in a positive $\Delta H_f$. Therefore,the heat of formation of compounds can be either negative or positive.

The heat of formation is the change in enthalpy accompanying the formation of a substance from its elements at $298 \ K$ and $1 \ atm$ pressure. Since the enthalpies of elements are taken to be zero,the heat of formation $(\Delta H_f)$ of compounds

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