Chemistry 111
Page 1 out of 7
Exam III /Fall 2002
Answer Key
Bonus
question:
Name today’s holiday.
Hint…
Kids go trick-or-treating all over the city and
get lots of candy.
☺
Halloween
Fill in the Blanks
.
Please, make sure you write your answer in the blank provided.
If it requires
a calculation, make sure you show all your work, or you will receive no credit for your answer.
1.
67.5 min
Let’s say that at the house of a certain math professor, he and his wife
hand out 250 pieces of candy in the first 5.00 minutes of a
Halloween
night.
Of course, the kids are terribly frightened because of his
ghoulish disguise but what they do not realize is that he is not wearing
a costume…
Anyhow, they have all together 2,500 pieces of candy.
Assuming that the candy will be dispensed following second order
kinetics, how long will it take before they have only the 1,000 pieces
he wants to keep for himself?
(14 pts)
Well, we are told that the disappearance of the candy follows second order kinetics.
This means that…
1
[A]
−
1
[A]
D
=
k t
We need to determine the rate constant (k) first.
For that, we use the information that he
dispenses 250 pieces of candy in 5.00 minutes.
Therefore, he has 2,250 pieces of candy left
after 5 minutes.
1
2,250 pieces
−
1
2,500 pieces
=
k
×
5.00 minutes
∴
k = 8.89
×
10
-6
pieces
-1
min
-1
.
Now, he wants to have 1,000 pieces left for himself to eat at a later time.
Therefore,
1
1,000 pieces
−
1
2,500 pieces
=
8.89
×
10
-6
pieces
-1
min
-1
×
t
∴
t =
67.5 minutes
.
2.
H
2
Both H
2
gas and butane gas (CH
3
CH
2
CH
2
CH
3
) are non-polar and
they both obey the ideal gas law.
Which of these two would you

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