Exercises
 Page ID
 54342
Section 82
Q81
A) You are driving down the street at a constant speed of 60mph.
Draw a graph of distance versus time over the course of 4 hours.
B) How would you use the graph to determine the rate (speed in mph) at which the car is travelling (assuming you did not already know the answer)? Hint: What is the slope for the graph in part A? What does the term slope mean?
C) Now draw a new graph (still distance vs. time). Assume that at t=1 hour you removed your foot from the accelerator, and that the car coasts to a stop after 1 hour (we know that is not realistic, just think about the shape of the curve.)
E) Does the car move at a constant rate (speed) as it is slowing down? Why or why not?
F) Why do the two graphs look different? (hint: they should look different)
G) In the time between t=1 and t=2, how would you estimate your speed (using the second graph you drew? (Why do we need to specify the time?)
Section 83
Q81
Consider the reaction A_{2} + B_{2} ⇌ 2AB. If the initial concentration of both A and B is 4 M, and after 10 minutes the reaction appears to stop. The concentration of [A] is now 2.0M.
A) Draw a graph of [A_{2}] v time, over the span of 20 minutes.
B) On the same axes draw a graph of [B_{2}] v time, over a span of 20 minutes
C) On the same axes draw a graph of [AB} v time over a span of 20 minutes
Q82
We can discuss the rate in terms of [A_{2}], [B_{2}], or [AB]. How are they related to each other? Δ[A_{2}]/Δt = ?
Q83
What is the difference between Δ[A_{2}]/Δt and d[A_{2}]/dt
Q84
At t = 15 minutes has the reaction stopped?
Section 84
Q81
Here are some concentration time data for a reaction. Determine the rate law for the reaction by plotting three graphs: You should use excel to plot the graphs. (just copy the data out of word and paste it into excel)
A) [A] v time,
B) ln[A] v time
C) 1/[A] v time.
Submit all graphs with your work.
Time (minutes) 
[A] (M) 
0.0 
0.55 
0.25 
0.42 
0.50 
0.31 
0.75 
0.23 
1.00 
0.17 
1.25 
0.12 
1.50 
0.085 
A) What is the order of the reaction with respect to [A]?
B) How would you calculate the rate constant?
Section 85
Q81
What set of concentrations would you use in order to determine the rate law for a given reaction?
Here is one set of conditions – fill out the rest of the table with enough sets of conditions to determine what the rate law is for the reaction
A + B à C + D
[A] mol/L 
[B] mol/L 
Initial rate mol/L.min 
1.0 
1.0 
1.0 









A) If the reaction is first order in A and 2^{nd} order in B, fill out the table with the rate you would expect.
[A] mol/L 
[B] mol/L 
Initial rate mol/L.min 
1.0 
1.0 
1.0 









B) If the reaction is first order in A and zero in B, fill out the table with the rate you would expect
[A] mol/L 
[B] mol/L 
Initial rate mol/L.min 
1.0 
1.0 
1.0 









C) If the reaction is first order in A and first order in B. fill out the table with the rate you would expect
[A] mol/L 
[B] mol/L 
Initial rate mol/L.min 
1.0 
1.0 
1.0 









How would you determine the initial rate of the reaction? What measurements would you record and how would you treat the data?
Q82
 Determine the order of the reaction and rate constant (k) based on the following data. The data are real data generated by watching the dissociation of a protein complex (PA_{20}·PA_{63}) to its separate subunits (PA_{20} and PA_{63}).
PA_{20}·PA_{63}→PA_{20} + PA_{63}
Time (min) 
[PA_{20}·PA_{63}] (μM) 
4.67 
0.98 
7.33 
0.81 
10.33 
0.73 
13.00 
0.65 
16.00 
0.60 
18.33 
0.56 
21.00 
0.49 
24.00 
0.55 
27.00 
0.42 
29.33 
0.37 
32.00 
0.38 
35.00 
0.32 
37.67 
0.39 
40.33 
0.33 
43.33 
0.33 
46.00 
0.28 
48.67 
0.28 
51.67 
0.31 
54.33 
0.20 
57.00 
0.19 
59.67 
0.20 
62.67 
0.24 
65.00 
0.24 
68.00 
0.19 
70.67 
0.21 
73.67 
0.19 
76.33 
0.16 
79.00 
0.13 
81.67 
0.15 
84.67 
0.14 
87.67 
0.19 
90.67 
0.17 
93.33 
0.19 
96.00 
0.15 
Section 86
Q81
If we say something (anything) is at equilibrium, what does that mean to you?
Q82
If a reaction is at equilibrium, what does that mean? (is it different than the definition you gave above?)
Q83
Consider the reaction A ⇌ 2B. The initial concentration of A is 4 M, and after 10 minutes the concentration of A is 2.0 M and does not change any further.
A) Draw a graph of [A] v time, over the span of 20 minutes, and on the same axes draw a graph of [B] v time, over a span of 20 minutes. Show where the reaction reaches equilibrium.
Q84
When the reaction reaches equilibrium, what is the relationship between the rate of the forward reaction and the rate of the reverse reaction?
Section 87
Q81
What does it mean when we say a reaction has reached equilibrium?
Q82
If ΔG for a system is = 0, what does that mean?
Q83
For the reaction A D B, as the reaction approaches equilibrium what happens to G (does it increase, decrease or stay the same?)
Q84
For the reaction A D B, if K = 1, what are the relative concentrations of A and B?
Q85
For the reaction A D B, for which K = 1. Draw a graph of how the Gibbs Free energy changes as the relative amounts of [A] and [B] change.
G
100% A 50% A 0%A
0% B 50% B 100%B
Section 88
Q81
A) Write out the equilibrium reaction for the ionization of Propanoic acid (CH_{3}CH_{2}COOH) in water.
B) What is the expression for Ka?
C) If the pH of a 0.15 M solution of propanoic acid is 2.8, what is the Ka? What is the pKa?
Q82
For the acid base reactions given, draw out the full reaction using Lewis structures and curved arrows to indicate how the proton transfer takes place.
Indicate whether the equilibrium position would lie to the right or the left.
pKa H2O = 15.7, NH_{4}+ = 9.8, NH_{3} = 33
A) NH_{3} + H_{2}O D NH_{4}^{+} + ^{–}OH
B) NH_{2}^{–} + H_{2}O D NH_{3} + –OH
Q83
Draw a reaction energy profile (H vs reaction progress) for an exothermic reaction.
 Label the axes, the transition state, reactants, products, DH, and the activation energy.
Section 89
Q81
A) What is the pH of a 0.25 M solution of NH4Cl? (Ka = 5.6 x 10^{–10})
B) If you added enough NH3 to make the solution 0.25 M solution in NH3, what would happen to the pH (assume the only reaction going on is the one you used in part 1a) – why?
C) Calculate the pH of a solution that is 0.25 M in both NH4Cl and NH3
Q82
For the reaction:
2NH_{3}(g) + CO_{2}(g) D (NH_{2})_{2}CO(s) + H_{2}O(l) ΔH = – 330 kJ
Predict the effect of the following on the position of equilibrium (use arrows to show the direction of change
A) Adding CO2
B) Adding (NH_{2})_{2}CO(s)
C) Increasing pressure
D) Increasing volume
E) Adding a catalyst
F) Adding some He(g)
G) Heating the reaction up.