Draw and label the parts of a potential energy

• draw and label the parts of a potential energy diagram.
Vocabulary
• endothermic reaction
• exothermic reaction
• internal energy
• potential energy diagram
Introduction
In this lesson, we go beyond the theoretical perspectives of the collision theory to consider how particle collisions
can be represented in energy diagrams. Potential energy diagrams are used in the study of kinetics to show how the
potential energy changes during collisions of reactants and products. The features of such diagrams will be the focus
of this lesson.
Internal Energy of Reactants and Products,
Δ
H
Potential energy diagrams illustrate the potential energy of the reactants and products for a chemical reaction and
how this energy changes during a reaction. Take a look at the potential energy diagram of the reaction shown below.
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18.3. Potential Energy Diagrams www. c k12 .org
The y -axis represents the potential energy. The potential energy measures the energy stored within the bonds and
phases of the reactants and products. This potential energy is a part of the internal energy. In chemical reactions,
the internal energy represents the total energy of the system and is often called enthalpy. The x -axis represents the
reaction progress. Chemical reactions proceed (or are read) from left to right. Therefore, looking at the potential
energy diagram, the reactants are usually found to the left on the diagram and the products on the right.
The enthalpy of a substance is sometimes called heat content. The potential energy stored in the bonds of the
substance was thought of as heat stored as potential energy. When a reaction occurs, the enthalpy or heat content of
the reactants changes into the enthalpy or heat content of the products. The enthalpy of the reactants and products
is almost never the same. Therefore, when a reaction occurs, there is a change in the amount of potential energy
stored in the bonds between the reactants and the products. If the bonds of the products store more energy than
the bonds of the reactants, then energy must be taken in during the reaction. If the bonds of the products store less
potential energy than the bonds of the reactants, then excess potential energy will be left over and will come out of
the reaction as kinetic energy. The difference in the enthalpy or heat content of the reactants and that of the products
is expressed as 4 H , or the change in enthalpy . Since this energy is either taken in or given off during the reaction,
it is also called the heat of reaction .
Exothermic and Endothermic Potential Energy Diagrams
There are two types of potential energy diagrams. These two types center on the difference between the energies
of the reactants and products. Consider the figure below. An endothermic reaction is shown on the left, and an
exothermic reaction is shown on the right.