Chemistry 102, Test Chapter 13-14 Worksheet With Answers - 1997 Page 5
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1112.(13)The reaction NO
(g) + CO(g)
NO(g) + CO
(g) has the rate law:
2
2
2
Rate = k[NO
]
. Which of the following mechanisms is consistent with this rate law?
2
1.
2 NO
+ 2 CO
2 NO + 2 CO
slow
2
2
2.
NO
+ NO
NO
+ NO
slow
2
2
3
NO
+ CO
NO
+ CO
fast
3
2
2
3.
NO
NO + O
slow
2
CO + O
CO
fast
2
4.
NO
+ NO
N
O
fast
2
2
2
4
N
O
+ 2 CO
2 CO
+ 2 NO
slow
2
4
2
2
Answer: 2.
Rate = k[NO2]
Look at the slow step (rate-determining
step) in each mechanism to determine the rate law:
+ 2CO → 2NO + 2CO
1. 2NO
Slow
2
2
2
2
This gives a rate law of: Rate = k[NO2]
[CO]
Does not match the rate law above.
→ NO
2. NO
+ NO
+ NO
Slow
2
2
3
2
This gives a rate law of: Rate = k[NO
][NO
] or Rate = k[NO
]
2
2
2
****This matches the given rate law
→ NO + O slow
3. NO
2
This gives a rate law of: Rate = k[NO
]
does not match the given rate law
2
→ N
4. NO
+ NO
O
Fast
2
2
2
4
+ 2CO → 2CO
N
O
+ 2NO Slow
2
4
2
2
This gives a rate law of: Rate = k[N
O
][CO]
N
O
is an intermediate
2
4
2
4
[N
O
] = [NO
][NO
] from step 1
2
4
2
2
2
Rate = k[NO
][NO
][CO]
Does not match the given rate law.
2
2
13.(5) Consider the data for several different reactions at a given temperature
Reaction
Ea (kJ/mol)
∆H(kJ)
1
40
-25
2
60
+30
3
15
+20
4
90
-55
Which is most likely the slowest exothermic reaction?
1. 1
2. 2
3. 3
4. 4
Answer: 4. 4
Note: See Problem 48, chapter 11
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