182.
What do you mean by enthalpy (heat) of reaction? Name the factors that influence the enthalpy of reaction.
The total amount of heat energy evolved or absorbed when the number of moles of reactants reacts completely to give the products as given in the balanced chemical equation is known as heat of the reaction. Since most of the reaction takes place at constant pressure, therefore, enthalpy change (∆H) is the heat of the reaction. For example,
Thus heat of the reaction is -393.5 kJ
At constant volume, ∆H= ∆U, therefore, internal energy change (∆U) is the heat of the reaction at constant volume. Hence heat of the reaction is expressed in two ways:
(i) Heat reaction is constant pressure (∆H).
(ii) The heat of reaction at constant volume (∆U).
Both these values are related by the equation
Factors affecting the enthalpy of a reaction:
(i) Temperature
(ii) Physical state of reactants and products
(iii) Allotropic forms of elements
(iv) Pressure and volume.
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