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Skills Worksheet
Concept Review
Section: What Affects the Rate of a Reaction?
Complete each statement below by choosing a term from the following list. Use
each term only once.
1.
time
chemical kinetics
volume
acidity
appearance
mass
decrease
positive
disappearance
reaction rate
is the decrease in reactant concentration or increase in
product concentration per unit of time as a reaction proceeds.
2. The study of reaction rates, called
, is one of the frontiers of
chemistry that provides an almost unlimited supply of opportunities for
chemical research.
3. Reaction rates can be noted and evaluated from the
reactant or the
of a
of a product per unit of
.
4. Three properties can be used to monitor the reaction rate in the following
chemical reaction:
Mg(s) 2H3O(aq) 2Cl(aq) £ Mg2(aq) 2Cl(aq) H2(g) 2H2O(l)
the
in
of solid Mg; the decrease in
, H3O ions, of the solution; and the
formed, all per unit of time.
of H2
5. The minus sign in the reaction-rate equation makes the decrease in reactant
concentration a
number.
6. Write the reaction-rate equation for the chemical reaction in item 4.
7. Refer back to the chemical reaction in item 4. If 0.048 g of magnesium
completely reacts in 20 seconds, what is the average reaction rate in mol/s
over that time interval?
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Holt Chemistry
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Reaction Rates
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Concept Review continued
In each blank next to the descriptions below, write the letter of the factor affecting
the rate of reaction.
a. temperature
c. nature of reactants
b. concentration
d. surface area
______ 8. A piece of steel wool heated in air (20% oxygen by volume) burns
slowly, but when heated in pure oxygen, it undergoes rapid combustion, as evidenced by a dazzling shower of sparks.
______ 9. Storing foods and milk in a refrigerator helps to slow down reactions
that ordinarily result in spoilage and souring.
______10. Powdered iron in melted sulfur reacts more rapidly than a lump of iron
in melted sulfur.
______11. When a piece of magnesium ribbon is placed in a beaker of dilute
hydrochloric acid, a rapid evolution of hydrogen gas occurs; when a
piece of iron is placed in the same acid, hydrogen gas is evolved
slowly, and the iron disappears at a relatively slow rate.
______12. Pressure cookers are used so that the reactions involved in cooking
food will take place at a faster rate.
Write your answer to the following questions in the space provided.
13. If the concentrations of the products in a reaction are increasing would the
signs of their rate expressions be positive or negative?
14. During a given chemical reaction explain how the following conditions may
affect the reaction rate in all states of matter.
a. concentration
b. pressure
c. temperature
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Holt Chemistry
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Reaction Rates
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Concept Review continued
15. How does surface area affect reaction rates? Explain your answer.
Solve the following problems, and write your answer in the space provided. Refer
to Table 1 (Concentration Data and Calculations for the Decomposition of N 2O5)
for concentration data.
16. Calculate the reaction rate of the decomposition of N2O5 between the time
intervals of 40.0 to 60.0 seconds.
17. Calculate the reaction rate of the decomposition of N2O5 between the time
intervals of 20.0 to 40.0 seconds.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Chemistry
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Reaction Rates
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TEACHER RESOURCE
Answer Key
Concept Review: What
Affects the Rate of a
Reaction?
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
4.
5.
6.
7.
8.
9.
10.
Reaction rate
chemical kinetics
disappearance, appearance, time
decrease, mass, acidity, volume
positive
reaction rate 1/1 ∆[Mg]/∆t 1/2 ∆H3O/∆t 1/1 ∆[H2]/∆t
average rate (0.002 mol Mg)/20s 0.0001 mol/s
b
a
d
c
a
positive
a. usually the reaction rate will
increase as the concentration of the
reactants increases in all states of
matter.
b. has almost no effect on reactions in
the liquid or solid states. In the gas
phase, an increase in pressure
increases the concentration, therefore increasing the reaction rate.
c. in almost all cases and in all states
of matter, an increase in temperature will increase the reaction rate.
For reactions on surfaces an increase
in surface area increases the reaction
rate. This is due to the fact that the
reaction rate is proportional to the
surface area, a higher surface area
allows an increased amount of the
reaction to occur.
4.775 105 M/s
5.275 105 M/s
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
Concept Review: How Can
Reaction Rates Be
Explained?
n, m
n, m
n
B
n, m
n, m
a. 1
b. 3⁄2
c. 2,
d. 3
increase, 2
increase, 27
1
⁄4, 3
In order for a reaction to occur, the
molecules or atoms must collide with
sufficient energy to overcome the activation energy barrier. And the collision
must occur in the correct orientation,
or in most cases at a particular end of
a molecule or atom, in order for a
reaction to occur.
rate k[AB]
rate k[B]2
rate k[A2]
2NO H2 £ N2 H2O2
Step 1, the slower step
O3 £ O2 O rapid
O O3 £ 2O2 slow
15 kcal
35 kcal
The label should be placed at the peak
of the curve.
exoendoa
b
e
c
f
d
catalytic converter
lower activation energy, accelerate
regenerated
1. 2. k
3. [A], [B]
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Chemistry
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Reaction Rates