CHEM 1123 – Comprehensive Final Study Guidance

Q26. Show the energy of activation on the graph below. Is the reaction exothermic or endothermic?

Background

Topic: Reaction Energy Diagrams

This question tests your understanding of reaction energy diagrams, specifically how to identify the activation energy and determine whether a reaction is exothermic or endothermic based on the relative energies of reactants and products.

Key Terms and Concepts:

• Activation Energy (Ea): The minimum energy required for a reaction to proceed, represented by the energy difference between the reactants and the highest point on the curve.

• Exothermic Reaction: A reaction where the products have lower energy than the reactants (energy is released).

• Endothermic Reaction: A reaction where the products have higher energy than the reactants (energy is absorbed).

Step-by-Step Guidance

1. Examine the energy diagram. Identify the starting point (reactants) and the ending point (products) on the y-axis (energy).

2. Locate the highest point on the curve between reactants and products. This peak represents the transition state.

3. Draw or imagine a vertical arrow from the reactants' energy level up to the peak. This vertical distance is the activation energy ($E_a$).

4. Compare the energy of the products to the energy of the reactants. If the products are lower, the reaction is exothermic; if higher, it is endothermic.

Try solving on your own before revealing the answer!

Final Answer:

The activation energy is the vertical distance from the reactants to the peak of the curve. Since the products are lower in energy than the reactants, the reaction is exothermic.