Which expression represents the ∆H for a chemical reaction in terms of the potential energy, PE, of its products and reactants? A) PE of products + PE of reactants B) PE of products – PE of reactants C) PE of reactants × PE of products D) PE of products ÷ PE of reactants E) PE of reactants – PE of products

QUESTION POSTED AT 01/06/2020 - 02:51 PM

Answered by admin AT 01/06/2020 - 02:51 PM

The answer is the option B) PE of products - PE of reactants.

This is, the change of energy, in the form of heat, ΔH, for a chemical reaction is the potential energy of products less the potential energy of reactants: ΔH = PE products - PE reactants.

Note that this leads to:

1) when the potential energy increases, PE of products - PE of reactants > 0 => ΔH > 0, =>the reaction is absorbing energy and it is endothermic;

2) when potential energy decreases PE of products - PE of reactants < 0 => ΔH < 0, the reaction is releasing energy and it is exothermic.

Those are terms very used in chemistry and thermodynamics.
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