Energy and Rates of Chemical Reaction Questions

1. The potential energy diagram shown is for the reaction C à A + B. Is this reaction exothermic or

endothermic? Select the number on the diagram that indicates the

a.  activation energy;

b.  potential energy of the reactant;

c.  energy change for the reaction.

Reaction progress over time

2. If a 100C rise in temperature approximately doubles the rate of a chemical reaction, how would you

expect the rate of the reaction at 300C to compare with the rate of the same reaction at 00C?

3. Why will a mixture of hydrogen and chlorine gases react faster when the volume they occupy is

decreased?

4. A student describes the burning of a candle as an endothermic reaction because it takes heat to

light the candle. Is this a correct description? Explain.

5. How is the activation energy of a reaction like a wall or barrier?

6. How is the rate of a reaction influenced by a catalyst? How do catalysts make this possible?

7. Which of these statements is true? For those that are not true, explain why.

a. Chemical reactions can be slowed down by increasing the temperature.

b. Once a chemical reaction gets started, the reacting particles no longer have to collide for

products to form.

c.Enzymes are biological catalysts.

8. Sketch a reaction progress curve, graph, for a reaction that has an activation energy of 22 kJ, and

the total energy change is -103 kJ.

9. For the reaction A + B ↔ C, the activation energy for the forward reaction is 5 kJ and the total

energy change is -20 kJ. What is the activation energy of the reverse reaction?

10. When table sugar, or sucrose, is dissolved in an acidic solution, the sucrose slowly decomposes

into two simpler sugars: fructose and glucose. Use the graph to answer these questions.

Rate of Sucrose Decomposition

0 25 50 75 100 125 150

Time (min)

a.  How many grams of sucrose are decomposed during the first 30 minutes?

b.  How many grams of sucrose decompose in the 30-minute interval between 90 and 120 minutes?

c.  In general, what happens to the rate of decomposition with time?

11. How do the rates of the forward and reverse reactions compare at a state of dynamic chemical

equilibrium?

12. The following data were collected for the decomposition of compound AB into its elements.

[AB] (mol/L) / Time (s)
0.300 / 0
0.246 / 50
0.201 / 100
0.165 / 150
0.135 / 200
0.111 / 250
0.090 / 300
0.075 / 350

a.  Make a graph of the concentration versus time where concentration is the dependent

variable.

b.  How long will it take before the concentration of AB is 0.185 mol/L?

c.  What is the relationship between the concentration of AB versus time?