AP Chemistry · Topic 5.3
Concentration Changes Over Time Practice
Part of Kinetics.(TRA-3.C)
Practice questions
39
Sample questions
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Sample 1difficulty 1/5
The rate is independent of [A] (horizontal line on rate vs [A]). This indicates:
- Acheck_circle
Zero order in A
- B
First order in A
- C
Inverse order
- D
Second order in A
Why
For zero order, rate = k regardless of [A].
- A
Sample 2difficulty 1/5
The plot of rate vs [A] is linear with positive slope. The order in A is:
- A
Cannot tell from this plot alone
- Bcheck_circle
1
- C
0
- D
2
Why
rate = k[A] is linear in [A] with slope k for first order.
- A
Sample 3difficulty 2/5
A first-order reaction shows successive half-lives of 80 s on a [A] vs t plot.
For a first-order reaction, the half-life t1/2 = 80 s. After 240 s, what fraction of A remains?
- A
1/3
- Bcheck_circle
1/8
- C
1/16
- D
1/4
Why
240 s = 3 half-lives. (1/2)^3 = 1/8 remains.
- A
Sample 4difficulty 2/5
For which order is half-life independent of initial concentration?
- Acheck_circle
First
- B
Third
- C
Zero
- D
Second
Why
Only first-order reactions have constant half-life regardless of [A]₀.
- A
Sample 5difficulty 2/5
[A] starts at 1.00 M. At t = 100 s, [A] = 0.50 M. At t = 200 s, [A] = 0.25 M. At t = 300 s, [A] = 0.125 M.
What is the order of the reaction?
- A
Third order
- B
Zero order
- Ccheck_circle
First order
- D
Second order
Why
Constant half-life (100 s) regardless of starting concentration is the signature of first-order kinetics.
- A