Part 1
1. Consider the potential energy diagram shown below. This graph shows the chemical potential energy in a reaction system over time. The y–axis is potential energy in kilojoules. The x–axis is the reaction progress, or time.

a. Does this graph represent an endothermic or an exothermic reaction? Explain your answer.
b. What is the enthalpy change, ΔH, for this reaction? Show your work.
c. What is the activation energy, Ea, for this reaction? Show your work.

Part 2
2. In a particular chemical reaction, the energy of the reactants is 30 kJ and the energy of the products is 5 kJ. The maximum energy of the system is 40 kJ. Use this information to answer questions a – d.
a. Sketch a potential energy diagram for this reaction. Make sure to label the energy of the reactants, the energy of the products, the activation energy, and the enthalpy change for the reaction. (Note: You may use the graph provided below or sketch your own. Resize as needed.)


b. What is the activation energy for this reaction?
c. What is the enthalpy change for this reaction?
d. Is this reaction endothermic or exothermic? Explain your answer in two ways: first, using the energy values, and second, by referring to the shape of the graph.

Part 3
3. The coating on the head of a match is highly flammable. When it burns, it releases a great deal of energy. However, before the match can burn, it must gain a small amount of energy from a spark. That spark is typically produced by striking (rubbing) the match head against a rough surface.
a. Sketch a potential energy diagram that represents the striking and burning of the match. Remember to label the diagram with the energy changes that occur. (Note: you do not have to use actual energy values. And you may use the graph provided below or sketch your own.)

b. Describe a potential energy diagram that represents the striking and burning of the match.