AQA GCSE FOUNDATION Chemistry: Energy Profiles

GCSE Foundation Chemistry: Energy Profiles

This tutorial will explore energy profiles, focusing on activation energy and how to represent exothermic and endothermic reactions.

What is an Energy Profile?

An energy profile is a visual representation of the energy changes that occur during a chemical reaction. It shows the energy of the reactants, the energy of the products, and the activation energy needed for the reaction to occur.

Activation Energy (Ea)

Activation energy is the minimum amount of energy that reactant molecules need to collide with in order to react. It's like pushing a boulder uphill - you need to put in some energy to get it over the top.

Exothermic Reactions

• Energy released: In exothermic reactions, more energy is released when new bonds are formed in the products than is absorbed when bonds are broken in the reactants.
• Energy profile: The products have lower energy than the reactants, resulting in a downward slope on the energy profile. The energy difference between reactants and products represents the energy released.

Endothermic Reactions

• Energy absorbed: In endothermic reactions, more energy is absorbed when bonds are broken in the reactants than is released when new bonds are formed in the products.
• Energy profile: The products have higher energy than the reactants, resulting in an upward slope on the energy profile. The energy difference between reactants and products represents the energy absorbed.

Drawing Energy Profiles

1. Reactants: Start by drawing a horizontal line representing the energy of the reactants.
2. Products: Draw another horizontal line representing the energy of the products. This line will be lower for exothermic reactions and higher for endothermic reactions.
3. Activation energy: Draw a curved line connecting the reactants and products, with the highest point representing the activation complex. The difference in energy between the reactants and the activation complex is the activation energy (Ea).

Example Energy Profiles

Here are example energy profiles for an exothermic and an endothermic reaction:

Exothermic Reaction:

             Energy
              |
              |
              |                Activation Complex
              |     Ea        /
       Reactants   |     /
              |    /
              |   /
              |  /
              | /
       Products    |
              |___________________________________
                            Reaction progress

Endothermic Reaction:

             Energy
              |
              |
              |                Activation Complex
              |      Ea        /
       Reactants   |     /
              |    /
              |   /
              |  /
              | /
       Products    |
              |___________________________________
                            Reaction progress

Summary

Understanding energy profiles helps us to visualize the energy changes involved in chemical reactions. By comparing the energy levels of reactants and products, we can determine whether a reaction is exothermic or endothermic. The activation energy is crucial for determining how easily a reaction will proceed.