Have you ever learned about activation energy in your chemistry class? If yes, then you may have also come across the terms “potential energy diagram” or “activation energy hill”. You may have even wondered why activation energy is shown as PE (Potential Energy) on a PE diagram rather than KE (Kinetic Energy) when it is supposed to be the average KE required for two particles to react.
What Is Activation Energy?
Before diving into why activation energy is shown as PE on a PE diagram, let’s first understand what activation energy is. Activation energy, denoted as Ea, is the minimum amount of energy required to initiate a chemical reaction. In simpler terms, the reactant molecules need to collide with enough energy to break the bonds between them and form new bonds with other molecules to produce products.
Potential Energy Diagram
A potential energy (PE) diagram is a graph that shows the change in potential energy that occurs during a chemical reaction. The reactant molecules have higher potential energy than the product molecules. The PE energy diagram consists of an X-axis that represents the reaction progress while the Y-axis represents the amount of potential energy a system has.
The PE diagram is made up of a series of curves and lines – one for each step or intermediate in the reaction process. Generally, the vertical lines represent energy level changes, while the curves represent the intermediate state in a chemical reaction.
Activation Energy Hill
Now, the question arises why activation energy is shown as PE in a PE diagram. It is traditionally shown as a “hill” since the reactant molecules must absorb energy before they can react. The activation energy hill represents the energy required to reach the activated complex or transition state, which is a short-lived intermediate state that exists before the products and reactants get transformed into each other.
If we do not give the reactant molecules the required energy to reach the activation energy hill, then the reaction will not proceed, and it will be energetically unfavorable. Thus, it is essential to have a higher potential energy for the reactants to initiate the chemical reaction.
Example
Let’s take the example of the reaction between hydrogen and chlorine to form hydrogen chloride gas (H2 + Cl2 → 2HCl)
Hydrogen and chlorine, both of which are diatomic gases, have high energy bonds. Therefore, they require a significant amount of energy to break those bonds and form new HCl bonds. As the temperature increases, the kinetic energy of the reactant molecules also increases, which makes it easier to overcome the activation energy barrier required for the reaction to proceed.
The activation energy hill is represented as the distance between the energy of the reactants and the energy of the activated complex.
Conclusion
In conclusion, activation energy is an essential aspect of chemical reactions, and the activation energy hill on a potential energy diagram is a visual representation of the energy required to initiate a chemical reaction. It is shown as PE on a PE diagram since the reactant molecules must absorb this energy to transform into products, and this energy gives them the momentum required to react.
So, the PE of the reactants has to increase for the activation energy to be overcome, and the products have a lower PE since they need lower energy to exist. I hope this article has cleared your doubts on why activation energy is shown as PE on a potential energy diagram.
Why is Activation Energy Drawn In a Potential Energy Diagram In Reactions?
Have you ever learned about activation energy in your chemistry class? If yes, then you may have also come across the terms “potential energy diagram” or “activation energy hill”. You may have even wondered why activation energy is shown as PE (Potential Energy) on a PE diagram rather than KE (Kinetic Energy) when it is supposed to be the average KE required for two particles to react.
What Is Activation Energy?
Before diving into why activation energy is shown as PE on a PE diagram, let’s first understand what activation energy is. Activation energy, denoted as Ea, is the minimum amount of energy required to initiate a chemical reaction. In simpler terms, the reactant molecules need to collide with enough energy to break the bonds between them and form new bonds with other molecules to produce products.
Potential Energy Diagram
A potential energy (PE) diagram is a graph that shows the change in potential energy that occurs during a chemical reaction. The reactant molecules have higher potential energy than the product molecules. The PE energy diagram consists of an X-axis that represents the reaction progress while the Y-axis represents the amount of potential energy a system has.
The PE diagram is made up of a series of curves and lines – one for each step or intermediate in the reaction process. Generally, the vertical lines represent energy level changes, while the curves represent the intermediate state in a chemical reaction.
Activation Energy Hill
Now, the question arises why activation energy is shown as PE in a PE diagram. It is traditionally shown as a “hill” since the reactant molecules must absorb energy before they can react. The activation energy hill represents the energy required to reach the activated complex or transition state, which is a short-lived intermediate state that exists before the products and reactants get transformed into each other.
If we do not give the reactant molecules the required energy to reach the activation energy hill, then the reaction will not proceed, and it will be energetically unfavorable. Thus, it is essential to have a higher potential energy for the reactants to initiate the chemical reaction.
Example
Let’s take the example of the reaction between hydrogen and chlorine to form hydrogen chloride gas (H2 + Cl2 → 2HCl)
Hydrogen and chlorine, both of which are diatomic gases, have high energy bonds. Therefore, they require a significant amount of energy to break those bonds and form new HCl bonds. As the temperature increases, the kinetic energy of the reactant molecules also increases, which makes it easier to overcome the activation energy barrier required for the reaction to proceed.
The activation energy hill is represented as the distance between the energy of the reactants and the energy of the activated complex.
Conclusion
In conclusion, activation energy is an essential aspect of chemical reactions, and the activation energy hill on a potential energy diagram is a visual representation of the energy required to initiate a chemical reaction. It is shown as PE on a PE diagram since the reactant molecules must absorb this energy to transform into products, and this energy gives them the momentum required to react.
So, the PE of the reactants has to increase for the activation energy to be overcome, and the products have a lower PE since they need lower energy to exist. I hope this article has cleared your doubts on why activation energy is shown as PE on a potential energy diagram.