Question

Consider the following potential energy diagrams for two different reactions.

Which plot represents an exothermic reaction? In plot a, do the reactants on average have stronger or weaker bonds than the products? In plot b, reactants must gain potential energy to convert to products. How does this occur?

Short answer

Here, the plot a represents an exothermic reaction.

In plot a, the reactants have weaker bonds.

In plot b, the reactants gain energy to convert to products because it is an endothermic reaction and the breaking up of bonds of reactants needs energy.

Step-by-step solution

The change in Enthalpy for Plot a:

$\text{Changeinenthalpy=\hspace{0.17em}Enthalpyofproduct–Enthalpyofreactant}$

For plot a, the change in Enthalpy is negative.

Hence, the reaction is exothermic.

Here, the reactants have weaker bonds so they do not need the energy to get broken.

The change in Enthalpy for Plot b:

For plot b, the change in enthalpy is positive, therefore the reaction is endothermic.

Chemical reactions involve the formation and breaking up of bonds of reactants which results in energy changes.

In endothermic reaction (plot b) the reactant gain energy to form products.