SC 1. For each description on the left, select all of the descriptors on the right that apply. As a hint, the number of descriptors that apply to each description is indicated in brackets after the description.
Description |
Descriptor |
a. the criteria that apply to a chemical system in equilibrium (3 descriptors) |
1. open system |
b. a system in which matter is allowed to enter and leave (1 descriptor) |
2. closed system |
c. a shift to the right (1 descriptor) |
3. colour changing |
d. the changes to the following system in a sealed container when placed in an ice bath (2 descriptors) |
4. colour remaining the same |
e. the shaded region identified on the following graph (1 descriptor) |
5. equal rate of forward and reverse reactions |
|
6. forward reaction favoured |
|
7. reverse reaction favoured |
Program of Studies
SC 1.
Description a.
D1.1k. Students will
Description b.
D1.1k. Students will
Description c.
D1.3k. Students will
Description d.
D1.3s. Students will
Description e.
D1.3s. Students will
Hint
SC 1.
Description a.
What must you be able to accomplish and observe to study a system?
Description b.
What makes gaseous systems difficult to study?
Description c.
Which side of a reaction will experience an increase in concentration with this shift?
Description d.
What does Le Châtelier’s principle state?
Description e.
What happens to the concentrations of substances when a system reaches equilibrium?
SC 1.
Description |
Descriptor |
a. |
2, 4, 5 |
b. |
1 |
c. |
6 |
d. |
3, 7 |
e. |
5 |
Lesson(s) to Review
SC 1.
Description a.
Module 7 Lesson 1
Description b.
Module 7 Lesson 1
Description c.
Module 7 Lesson 6
Description d.
Module 7 Lesson 6
Description e.
Module 7 Lesson 1
SC 2. Write the balanced chemical equation for the system shown in the following graph at equilibrium.
Program of Studies
SC 2.
D1.2k. Students will
Hint
SC 2. How do the values for concentration identify the reactants and products? How does the change in concentration of each species help you identify mole ratios for the reaction?
SC 2.
A 2 B
The concentration of B at the beginning is 0; therefore, A is the only reactant. This is confirmed as the concentration of A drops over the time of the experiment.
The concentration of B increases until equilibrium is established, as is consistent with a product. The rate of change for A is one half that of B, indicating the mole proportions are 1A:2B
Lesson(s) to Review
SC 2. Module 7 Lesson 4
Use the following information to answer the next four questions:
C(g) + D2(g) 2 E(g) + F(g) + 100 kJ
CHANGES TO A SYSTEM
|
|
|
|
|
SC 3. Write the equilibrium law expression for the system described in the chemical equation shown.
Program of Studies
SC 3.
D1.4k. Students will
D1.3s. Students will
Hint
SC 3. What is the general rule to write equilibrium law expressions?
SC 3.
Lesson(s) to Review
SC 3. Module 7 Lesson 5
SC 4. Explain the effect that Change 5 listed above would have on the equilibrium.
Program of Studies
SC 4.
D1.3k. Students will
Hint
SC 4. Which reaction, forward or reverse, would enable the system to compensate for a stress like this?
SC 4. The forward reaction would be favoured to reduce the concentration of the added reactant until a new equilibrium was established. Therefore, the system would shift to the right.
Lesson(s) to Review
SC 4. Module 7 Lesson 6
SC 5. Which of the changes to the system listed would cause the equilibrium shown to shift to the right.
Program of Studies
SC 5.
D1.3k. Students will
Hint
SC 5. Which reaction, forward or reverse, would enable the system to compensate for a stress like this?
SC 5.
Change |
Rationale |
1 |
The forward reaction is exothermic; therefore, a reduction in temperature would favour the forward reaction in an attempt to replace the energy removed from the system by reducing the temperature. |
2 |
The lower number of particles is on the reactants side (2 moles versus 3 moles on the products side). The reduced pressure favours the forward reaction that results in more gaseous particles, which will increase the pressure in the system. |
5 |
See answer to SC 4 above. |
Lesson(s) to Review
SC 5. Module 7 Lesson 6
SC 6. State the change listed that will not shift this equilibrium.
Program of Studies
SC 6.
D1.3k. Students will
Hint
SC 6. What change in this list will have no effect on this or any equilibrium?
SC 6.
Change 5—Adding a catalyst will not shift an equilibrium; it will only reduce the time required for the system to reach equilibrium.
Lesson(s) to Review
SC 6. Module 7 Lesson 6
SC 7. Consider the following system at equilibrium, graph, and possible stresses:
PCl5(g) + heat PCl3(g) + Cl2(g)
STRESSES
1. addition of heat |
2. addition of an inert gas |
3. addition of Cl2(g) |
4. pressure of system increased by decreasing the volume |
Match each stress listed to locations A through D shown on the graph.
Program of Studies
SC 7.
D1.3s. Students will
Hint
SC 7. How would the concentration of each substance in the system initially change with stresses 2, 3, and 4?
SC 7.
Position on Graph |
Stress |
Rationale |
A |
1 |
The forward reaction is endothermic. The system will compensate for the stress by attempting to remove the additional energy by favouring the forward reaction. The graph shows the concentration of reactant decreasing, and the concentration of the products increasing. |
B |
4 |
All three gases demonstrate an increase in concentration—this could be attributed to the reduction in volume for the system. After the initial volume change, the side with fewer particles will be favoured. A shift to the left is predicted. The graph shows the concentration of products decreasing and the concentration of the reactants increasing. |
C |
2 |
Addition of an inert gas will not change the concentration of any component in the system and will not affect the equilibrium. No change is predicted (initially or as the system moves toward equilibrium). No change in concentration is observed on the graph. |
D |
3 |
The only substance to show a change in concentration initially is Cl2(g). As a result of the increase in the concentration of Cl2(g), the system is expected to shift to the left. The graph shows the concentration of products decreasing and the concentration of reactants increasing. |
Lesson(s) to Review
SC 7. Module 7 Lesson 6
Use the following additional information to answer SC 8 and SC 9.
A system at equilibrium contains SO2(g), O2(g), and SO3(g). The concentrations of gases in the system are 3.46 x 10–2 mol/L, 1.95 x 10–5 mol/L, and 1.73 x 10–2 mol/L respectively.
SC 8.Write the equilibrium expression for this system.
Program of Studies
SC 8.
D1.4k. Students will
D1.3s. Students will
Hint
SC 8. What is the balanced chemical equation for the equilibrium in this system?
SC 8.
Lesson(s) to Review
SC 8. Module 7 Lesson 5
SC 9. Use your answer to SC 8 to calculate the value for the equilibrium constant, Kc, for this system.
Program of Studies
SC 9.
D2.3k. Students will
Hint
SC 9. Are you given equilibrium concentrations for each component in the equilibrium?
SC 9.
Lesson(s) to Review
SC 9. Module 7 Lesson 5
SC 10. Consider the following chemical system and information:
2 NH3(g) N2(g) + 3 H2(g)
Gaseous ammonia is introduced into an evacuated flask to a concentration of 2.00 mol/L. At equilibrium the concentration of ammonia in the flask is 1.00 mol/L. Calculate the Kc for this system using these data.
Program of Studies
SC 10.
D2.3k. Students will
Hint
SC 10. Are you provided equilibrium concentrations for each component in the equilibrium? If not, how can you use the information provided to calculate the concentrations of all substances at equilibrium?
SC 10.
Concentration |
2 NH3(g) |
N2(g) |
+ 3 H2(g) |
|
Initial (mol/L) |
2.00 |
|
0 |
0 |
Change (mol/L) |
–1.00 |
|
+0.500 |
+1.50 |
Equilibrium (mol/L) |
1.00 |
|
0.500 |
1.50 |
Lesson(s) to Review
SC 10. Module 7 Lesson 5
SC 11.
Program of Studies
SC 11. a. D1.4k. Students will
SC 11. b. D2.3k. Students will
SC 11. c. D1.4k. Students will
Hint
SC 11. a. What does the magnitude of the exponent for the equilibrium constant suggest about the position of the equilibrium for this system?
SC 11.b. Are you provided equilibrium concentrations for each component in the equilibrium? If not, how can you use the information provided to calculate the concentrations of all substances at equilibrium?
To develop your ICE table, let x equal the change in the concentration of hydrogen.
SC 11.c. How does the magnitude of the exponent for the equilibrium constant support the calculations shown in your ICE table?
SC 11.
Concentration |
H2(g) |
+Cl2(g) |
2 HCl(g) |
|
Initial (mol/L) |
0.500 |
0.500 |
|
0 |
Change (mol/L) |
–x |
–x |
|
+2x |
Equilibrium (mol/L) |
0.500 – x |
0.500 – x |
|
2x |
Simplify the expression by taking the square root of both sides.
Collect like terms and solve for x.
x = 0.500 mol/L
Complete the ICE table to calculate the equilibrium concentration for each gas.
Concentration |
H2(g) |
+Cl2(g) |
2 HCl(g) |
|
Initial (mol/L) |
0.500 |
0.500 |
|
0 |
Change (mol/L) |
–0.500 |
|
–0.500 |
+1.00 |
Equilibrium (mol/L) |
0.000 |
0.000 |
|
1.00 |
Lesson(s) to Review
SC 11.a.
Module 7 Lesson 5
SC 11.b.
Module 7 Lesson 5
SC 11.c.
Module 7 Lesson 5
SC 12. For each description on the left, match all of the chemical formulae on the right that apply. As a hint, the number of chemical formulae that apply to each description is indicated in brackets after the description:
Description |
Chemical Formula |
a. ___ and ___ are a conjugate pair. (6 possible pairs) |
1. HNO3(aq) |
b. amphiprotic species (4 chemical formulae) |
2. CH3COOH(aq) |
c. monoprotic species (5 chemical formulae) |
3. CH3COO–(aq) |
d. polyprotic species (2 chemical formulae) |
4. HS–(aq) |
e. can behave as a Brønsted-Lowry acid (7 chemical formulae) |
5. H2PO4–(aq) |
f. can behave as a Brønsted-Lowry base (8 chemical formulae) |
6. HPO42–(aq) |
g. A mixture of ___ and ___ form a buffer. (3 possible pairs) |
7. H3O+(aq) |
|
8. OH–(aq) |
|
9. H2O(l) |
|
10. NO3–(aq) |
|
11. S2–(aq) |
Program of Studies
SC 12.
a. D1.7k. Students will
b. D1.7k. Students will
c. D1.6k. Students will
d. D1.6k. Students will
e. D1.5k. Students will
f. D1.5k. Students will
g. D1.8k. Students will
Hint
SC 12.
SC 12.
Description |
Chemical Formula |
a. |
1. and 10. |
b. |
4., 5., 6., 9. |
c. |
1., 2., 7., 8., 9. |
d. |
5., 11. |
e. |
1., 2., 4., 5., 6., 7., 9. |
f. |
3., 4., 5., 6., 8., 9., 10., 11 |
g. |
2. and 3. |
Lesson(s) to Review
SC 12.
SC 13. Write the balanced chemical reaction and predict the position of the equilibrium for the following substances when combined.
Program of Studies
SC 13.
D1.6k. Students will
Hint
SC 13. How can the position on the Table of Relative Strengths of Acids and Bases be used to predict the products of an acid-base reaction and the position of its equilibrium?
SC 13.
Lesson(s) to Review
SC 13. Module 8 Lesson 3
SC 14. Sketch the titration curve for the titration of aqueous ethanoic acid with aqueous sodium hydroxide. On your sketch identify the location of the equivalence point and of the buffering regions. Explain chemically what is occurring at each of these locations on the titration curve.
Program of Studies
SC 14.
D1.3s. Students will
Hint
SC 14. How does the strength of the chemical components in a reaction influence the shape of a titration curve?
SC 14.
Lesson(s) to Review
SC 14. Module 8 Lesson 6
SC 15. Complete the following table comparing acids to their conjugate:
Substance |
Ka |
Conjugate |
Kb |
H2C6H6O6(aq) |
9.1 × 10–5 |
|
|
|
|
B(aq) |
4.2 × 10–6 |
Program of Studies
SC 15.
D2.2k. Students will
Hint
SC 15. What is the relationship between Kw, Ka, and Kb?
SC 15.
Substance |
Ka |
Conjugate |
Kb |
H2C6H6O6(aq) |
9.1 × 10–5 |
HC6H6O6–(aq) |
1.1 × 10–10 |
HB+(aq) |
2.4 × 10–9 |
B(aq) |
4.2 × 10–6 |
Lesson(s) to Review
SC 15. Module 8 Lesson 4
SC 16. Predict the [H3O+(aq)], [OH–(aq)], pH, and pOH for a 0.125–mol/L solution of
benzoic acid, C6H6COOH(aq).
Program of Studies
SC 16.
D2.2k. Students will
Hint
SC 16. Benzoic acid is a weak acid. Do you have to consider the assumption (approximation rule) described on page 741 of the textbook to perform these calculations?
SC 16. C6H6COOH(aq) + H2O(l) C6H6COO–(aq) + H3O+(aq)
Benzoic acid is a weak acid.
The assumption holds, meaning that the extent of ionization of the benzoic acid is very small in relation to its molar concentration; therefore, you can approximate the equilibrium concentration of the benzoic acid at equilibrium to be 0.125 mol/L.
Concentration (mol/L) |
C6H6COOH(aq) |
C6H6COO–(aq) |
+ H3O+(aq) |
|
Initial |
0.125 |
|
0 |
0 |
Change |
–x |
|
+x |
+x |
Equilibrium |
(0.125 – x) = 0.125 due to approximation |
|
x |
x |
Therefore,
Lesson(s) to Review
SC 16. Module 8 Lesson 4