Endothermic reactions

Kinetics – Potential Energy Diagrams
Potential energy diagrams are used to represent potential energy changes that take place as time
progresses during chemical reactions. The potential energy diagrams for the exothermic reaction
between substances X and Y is shown below. The reaction progresses from stage 1 (reactants),
through stage 2 (activated complex to), to stage 3 (products).
Exothermic Reaction
1. From the word list to
the right, select the term
that describes the
energy represented by
each lettered interval
(A, B, C, D, E ) in the
diagram, and write that
term in the space beside
the letter (PE refers to
Potential energy).
X + Y
XY + energy
Word List
Energy of activation
PE of products
PE of activated complex
Heat of reaction
PE of reactants
2. How do substances X and Y acquire increased potential energy as they move from stage 1 to
stage 2? ______________________________________________________________________
3. What happens to particles that meet or exceed the activation energy needed for a given reaction?
4. Under what two conditions do colliding particles fail to form the activated complex?
Endothermic reaction
5. Label the drawing with the letters A, B, C, D, E letting
each letter stand for the following intervals:
A = PE of products;
B = energy of activation;
C = PE of reactants;
D = heat of reaction;
E = PE of the activated complex
6. Which labeled section on the diagram for the
endothermic reaction shows the most significant
difference between the diagrams for the exothermic vs.
endothermic reactions? __________________
Explain _______________________________________
Exothermic reaction
Reaction Coordinate
X + Y + energy
7. On the diagram below, draw a dotted line to show the pathway of a catalyzed reaction. Add the
label C' to show the interval that represents the activation energy for the catalyzed reaction.
Reaction Coordinate
8. What is the name of the part of the diagram for the catalyzed pathway that is most changed from
that on the diagram for the non-catalyzed pathway? _____________________________
Explain why it is changed. ________________________________________________________
9. What affect does this change have on the rate of the reaction?_____________________________
10. According to the collision theory, why does the presence of a catalyst increase the rate of a