SCH4U1
Reaction Mechanisms
1.
Consider the following reaction that occurs in the atmopshere on a smoggy day:
NO
+
O
3
NO
2
+
O
2
r = k{NO]
Which of the following mechanisms is consistent with this rate law?
Explain.
a) NO
+
O
3
NO
2
+
O
2
(slow)
b)
NO
N
+
O
(slow)
N
+
O
3
NO
2
+
O
(fast)
O
+
O
O
2
(fast)
NO
+
O
3
NO
2
+
O
2
(overall)
c) O
3
O
2
+
O
(slow)
O
+
NO
NO
2
(fast)
NO
+
O
3
NO
2
+
O
2
(overall)
Surface Area and Rate
1. A manufacturer of fireworks containing powdered magnesium wants to achieve a
somewhat longer duration for the burn period. Can you suggest a possible way to do
this?
2.
CH
4
+
O
2
CO
2
+
2 H
2
O
If the concentration of oxygen is doubled, the rate of this reaction will be:
a) double the original rate.
b) half the original rate.
c) four times the original rate.
d) impossible to determine without more experimental information.
3 a) Calculate the total surface area of a wooden cube with 10.0 cm long sides.
b) Calculate the total surface area if the cube is cut into 1000 smaller cubes.
c) Calculate the total surface area if each of the smaller cubes is again subdivided into
1000 mini cubes.
d) If the cubes of a) b) and c) were burned, how would the rates of these reactions
compare?
4.
A cube with a surface area of 864 cm
2
takes 60 minutes to dissolve in a liquid.
An
identical cube is divided into 216 smaller cubes and these cubes take only 10 minutes
to dissolve. What are the dimensions of the smaller cubes?
Hint:
SA
cube
= 6x
2
where x
is the length on a side.
5. A block of wood burns in 75 minutes. An equivalent amount of sawdust burns in 15
minutes. If the surface area of the sawdust was 125 cm2, what was the surface area of
the block of wood?
Answers:
1.
b) since slow reaction is the ratedetermining step and it contains NO.
1.
Use granular Mg (less SA)
2. d)
(need rate law equation; not solid reactants)
3.
a) 600 cm
2
b) 6.00 x 10
3
cm
2
c) 6.00 x 10
4
cm
2
d) 10 x , 100x and 1000x faster
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2.0 cm x 2.0 cm x 2.0 cm
5. 25 cm
2
SCH4U1
CATALYSTS
A catalyst is a substance which speeds up a reaction without being used up itself.
It speeds up the reaction by changing the reaction mechanism to one which requires
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 Spring '10
 White
 Reaction, Catalysis, Chemical reaction

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