Question

Give definition of enthalpy of reaction and heat of formation.

Answer 1

Enthalpy of reaction:- The standard enthalpy of reaction (denoted ΔHr⦵) is the enthalpy change that occurs in a system when matter is transformed by a given chemical reaction, when all reactants and products are in their standard states.

Heat of formation:- The standard heat of formation is defined as the amount of heat absorbed or evolved at 25° C (77° F ) and at one atmosphere pressure when one mole of a compound is formed from its constituent elements, each substance being in its normal physical state.

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Answer 2

When the matter inside a system undergoes a chemical reaction, the enthalpy change that happens in that system is the enthalpy of a reaction.

For this condition, all the products and reactants should exist in their standard state.

The heat of formation means the amount of heat that is being absorbed or evolved when a mound of a substance is formed from its former elements.