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What energy changes take place during a chemical reaction?

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Recall that potential energy is stored energy. One type of stored energy, called chemical potential energy, is energy that is stored within the chemical bonds of a substance. Bond energy is a measure of the bond strength of a chemical bond and is the amount of energy needed to break apart the atoms involved in the bond. A higher bond energy means that it is a stronger bond.

During a chemical reaction, the bonds in the reactants are broken and new bonds are formed to make the products. This process requires the addition and release of energy. It takes energy to break the bonds in the reactants. This is necessary for all reactions. The energy required to break these bonds is called the activation energy. You can think of the activation energy as a hill that the reactant particles must climb in order to form products.

Look at this Example

Question

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Graph - Image description in following section.

Graph in which the y-axis is labelled “energy,” and the x-axis is labelled “progress.” The graph curves up from the particle as a reactant on the left to the particle at the peak of the curve in the middle, then down to the particle as a product on the right. An arrow labelled (EA) goes from the energy of the reactants to the peak of the curve.

This graph represents a reaction by showing a reactant particle that is gaining energy to get up a “hill” and then losing energy as it goes down the “hill.” What label on the graph represents the activation energy?

The energy difference between the ball at its highest point and the starting position of the ball represents the activation energy. This is represented by EA on the graph. This is the energy that is needed to break the bonds to start a reaction.