Simulation Activity: Energy Changes in Chemical Reactions Mark as Favorite (87 Favorites)

ACTIVITY in Classification of Reactions, Chemical Change, Temperature, Exothermic & Endothermic, Activation Energy, Energy Diagrams, Bond Energy. Last updated July 25, 2023.


In this simulation, students will evaluate the energy changes in an endothermic and an exothermic chemical reaction. Through the use of this simulation students will have the opportunity to compare how energy is absorbed and released in each reaction. Additionally, students will make a connection between the standard energy diagrams associated with each reaction type.

Grade Level

High and middle school

NGSS Alignment

This simulation will help prepare your students to meet the performance expectations in the following standards:

  • MS-PS1-5: Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
  • HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
  • Scientific and Engineering Practices:
    • Using Mathematics and Computational Thinking


By the end of this simulation, students should be able to

  • Differentiate between endothermic and exothermic chemical reactions
  • Identify processes as either exothermic or endothermic based on evidence, such as temperature changes in a chemical reaction
  • Associate an endothermic and exothermic chemical reaction with their related energy diagram
  • Understand how a chemical reaction is related to an energy diagram

Chemistry Topics

This lesson supports students’ understanding of

  • Energy
  • Endothermic
  • Exothermic
  • Energy Diagram
  • Chemical Reactions


Teacher Preparation: minimal

Lesson: 30-45 minutes



  • No specific safety precautions need to be observed for this activity.

Teacher Notes

  • This simulation could be used in a teacher-lead lecture, or it could be used as a student activity.
  • The size of the arrows entering and exiting the particles in the reaction should be noticeably different in size in an effort to correspond with the particular reaction type.
  • This simulation could be beneficial for simple understand of particle rearrangement in a double replacement reaction, if needed, rather than a focus on the energy changes
  • Teachers should ignore the presence of the energy diagram shown on the screen if it isn’t appropriate or is too advanced for the student audience.
  • This simulation was inspired by an ACS Middle School Chemistry Lesson.

For the Student


In this investigation you will examine two chemical reactions. You will be asked to answer questions as you navigate through the steps of the simulation. You can find the simulation here:

Exothermic Chemical Reactions: Make sure the Exothermic tab is chosen to begin.

  1. Click the orange button to “Break Bonds.” What is needed in order to break a chemical bond?
  2. When the particles rearrange during the chemical reaction, to create new bonds, why do they pair up like this? What is being represented in this step?
  3. In the overall reaction, what do you notice about the energy associated with the reactants and the energy associated with the products?
  4. What observation best represents this exothermic chemical reaction?
    1. A reaction takes place and the temperature of the mixture increases.
    2. A reaction takes place and the temperature of the mixture decreases.

  5. How does the energy diagram image shown relate to the chemical reaction?
  6. The prefix “exo” means external or outside, how does this relate to the exothermic chemical reaction that you just observed?

Endothermic Chemical Reactions: Click on the endothermic tab to begin.

  1. Before clicking the orange button to “Break Bonds.” How has the energy diagram changed? What is noticeable about the reactants in particular?
  2. Play the reaction. What do you notice about the energy changes between the reactants and the products in this reaction?
  3. If you observed a chemical reaction take place and the product was very cold, would this be an endothermic or an exothermic reaction?

Comparing Endothermic and Exothermic Chemical Reactions:

  1. The activated complex is the point on the graph that indicates that the reactants transition into products. Identify the point on the graph that you think might represnet the activated complex.
  2. Which type of reaction needs more energy (activation energy) added to the reactants to begin?
  3. Draw a sketch of both types of energy diagrams and indicate the activation energy for each.