Reaction profiles are diagrams that show the energy changes that occur during a chemical reaction. They help GCSE Chemistry students understand exothermic reactions, endothermic reactions and activation energy. Reaction profile diagrams are commonly used in exam questions and are an important part of the Energy Changes topic.
Summary
- Reaction profiles show how energy changes during a reaction.
- The vertical axis shows energy.
- The horizontal axis shows the progress of the reaction.
- All chemical reactions require activation energy.
- Exothermic reactions have products at a lower energy level than reactants.
- Endothermic reactions have products at a higher energy level than reactants.
- Reaction profiles are commonly used in GCSE exam questions.
What are Reaction Profiles?
A reaction profile is a diagram that shows the energy changes that occur during a chemical reaction. By comparing the energy of the reactants and products, students can determine whether a reaction is exothermic or endothermic. With the y-axis representing energy and the x-axis the progress of the reaction, the highest point on the curve represents the activation energy and the difference between reactants and products shows the overall energy change. For further details on exothermic and endothermic reactions please see our exothermic reactions guide and endothermic reactions guide
Parts of a Reaction Profile Diagram
- Reactants – substances present before the reaction starts.
- Products – substances formed during the reaction.
- Activation energy – minimum energy needed for a reaction to occur.
- Overall energy change – difference between reactants and products.
Being able to identify these features is an important GCSE Chemistry skill.
When drawing or annotating reaction profiles, use the specific reactants and products that given in the relevant chemical equation rather than just the generic words ‘reactants’ or ‘products’
| Feature | What It Shows |
| Reactants | Starting substances |
| Products | Substances formed |
| Activation Energy | Minimum energy needed for reaction to occur |
| Overall Energy Change | Difference between reactants and products |
Exothermic Reaction Profiles
Exothermic reactions transfer energy to the surroundings. On the reaction profile diagram, the products are shown at a lower energy level than the reactants because energy has been released. Examples include combustion, respiration and neutralisation reactions.
Endothermic Reaction Profiles
Endothermic reactions transfer energy from the surroundings. On the reaction profile diagram, the products are shown at a higher energy level than the reactants because energy has been absorbed. Examples include photosynthesis, thermal decomposition and instant cold packs.
Activation Energy
All chemical reactions require activation energy before they can begin. Activation energy is the minimum amount of energy needed for a reaction to occur. Every reaction has an activation energy with some reactions requiring more energy than others. Activation energy can be thought of as a hill that reactant particles must overcome before a reaction can occur. Activation energy is covered in more detail in our Activation Energy GCSE guide (coming soon).
How to Interpret Reaction Profile Diagrams
- Identify the energy level of the reactants.
- Identify the energy level of the products.
- Locate the activation energy.
- Decide whether the reaction is exothermic or endothermic. If the products are lower than the reactants, the reaction is exothermic. If the products are higher than the reactants, the reaction is endothermic.
Common GCSE Exam Mistakes
- Confusing activation energy with overall energy change.
- Mixing up exothermic and endothermic reaction profiles.
- Forgetting that all reactions require activation energy.
- Drawing endothermic profiles with products lower than reactants.
- Sloppily drawn arrows for activation energy and energy change.
Exam Tips
- Learn the difference between activation energy and overall energy change.
- Practise identifying whether a reaction is exothermic or endothermic.
- Always label activation energy clearly.
- When drawing the arrows on the diagrams ensure they always start from the same height as the reactants, the activation energy line must touch the highest point on the curve, the overall energy change must go to the same height as the products.
- Remember exothermic products are lower than reactants.
How Reaction Profiles Link To Other GCSE Chemistry Topics
- Energy changes
- Exothermic reactions
- Endothermic reactions
- Activation energy
- Bond energy calculations
Final Thoughts
Reaction profiles are an important part of GCSE Chemistry because they help students visualise energy changes during reactions. Understanding activation energy and the difference between reactant and product energy levels will help students answer a wide range of GCSE exam questions. For a detailed view of our full range of topics, see our GCSE Chemistry revision guide.
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