Acc Chem Unit #12 Plan Reaction Rates

HON CHEM Name ______UNIT #11B – Equilibrium

I) Assignments / Handouts A) Video worksheet “Molecules in Action” (required pg 3) B) Chapter 18 text ws (required pg 4-5) C) Equilibrium practice (required pg 6-8) D) Equilibrium problems (required pg 9-12) E) LeChatelier’s lab F) TBA

II) Text Support (Chapter 18 – Sections 18.3 and 18.4) Emphasis for unit 11B is on equilibrium. Complete the study guide for chapter 18 in your hw packet. It is a mostly based on concepts covered in section 18.3. A separate mini-unit (#11C) on quantitatively determining solubility product constant (Ksp) problems covered in section 18.4 will follow.

II) Learning Targets (I can …) A) Differentiate between equilibrium systems and systems not in equilibrium. B) Describe various equilibrium systems both macroscopically and microscopically. C) Describe the effects that changes in concentration, pressure, temperature, and catalysts have on systems in equilibrium. D) Use LeChatelier’s Principle to qualitatively predict shifts in various equilibrium systems in response to changing conditions. E) Write Ke and Ksp expressions for equilibrium systems. F) Quantitatively solve problems using Ke and Ksp expressions. G) Identify equilibrium shifts by analyzing information on graphs. H) Identify and describe equilibrium systems in our environment.

III) Tentative Schedule Mon 4/25 Intro to equilibrium Tue 4/26 LeChatelier’s Principle Lab Wed 4/27 LeChatelier’s post lab; equilibrium shifts Thu 4/28 Equilibrium – Q and A on homework problems Fri 4/29 Ke expressions Mon 5/2 Q and A Tue 5/3 Exam #11A&B (Equil and Reaction Rates) Unit #11A and B HW packet due Wed 5/4 Intro to solution equilibrium Ke and Ksp problems

IV) On-line support Science Geek Website at www.sciencegeek.net (choose chemistry homepage from menu on left) Interactive practice activities Unit #5 – Reaction Energy and Kinetics (the section below is a good fit this unit of study)  LeChatelier’s Principle  Unit 5 Review - mostly reaction rates (kinetics) and equilibrium

ChemTeam website (equilibrium) www.chemteam.info This website may help you in your quest to understand chemistry. Explanations can get quite involved – depending on the topic. It may be helpful at the introductory level. It will be especially helpful if you are looking for extra detail.

Engineering Challenge Your task to is design a system that maximizes the production of ammonia (NH3) which ultimately will be used in the production of fertilizer to spread across the great state of Iowa.

Ammonia is produced according to the following equation: N2(g) + 3 H2(g) ↔ 2 NH3(g) + Energy

Manipulate the following variables  Temperature  Pressure  Concentration  Catalyst Consider the effects of these variables on both reaction equilibrium and reaction rate. Be prepared to defend the design of your system.

The World of Chemistry – Episode 14 “Molecules in Action” 1. What is the basis of all chemical reactions?

2. What is necessary for successful collisions?

3. What is meant by activation energy?

4. How are activation energies affected by catalysts?

5. What is true about a catalyst at the end of a chemical reaction?

6. What is meant by equilibrium?

7. What does Le Chatelier's Principle tell us about equilibrium reactions?

8. What is the reaction involved in the Haber Process?

9. Why is this reaction important?

10. What conditions are used to increase the yield in the Haber Process?

Chapter 18 text study guide (sect 18.3 and 18.4) - EQUILIBRIUM ______: Reaction in which reactants form products, and products form reactants simultaneously.

______: Forward and reverse reactions are taking place at the same rate.

Conditions for equilibrium 1. Balance between reactants and products. 2. Rate of forward reaction = rate of reverse reaction 3. Closed system (nothing added or removed)

Equilibrium position is indicated by the concentrations of reactants and products when a system is in equilibrium. ______are favored when the forward reaction is more likely to happen. ______are favored when the reverse reaction is more likely to happen.

______: If a stress is applied to a system in equilibrium, the system will change to relieve the stress. (If a system in equilibrium is subjected to a change, processes occur to counteract that change.)

3 types of stress: Changes in concentration, temp, or pressure 1. Change in concentration: a. Adding a substance pushes the reaction in the opposite direction. (Shift away from what you add.) b. Taking away a substance pulls the reaction towards the removed substance. (Shift toward what you take away.)

3 H2 (g) + N2 (g) ↔ 2 NH3 (g)

What happens if you add H2? ______Take some away? ______

What happens if you add NH3? ______Take some away? ______

2. Change in temperature: a. Increasing the temp causes the equilibrium to shift in the direction that absorbs energy. (Shift away from what you add.) b. Decreasing the temp causes the equilibrium to shift in the direction that releases energy. (Shift toward what you take away.)

2 SO2 (g) + O2 (g) ↔ 2 SO3 (g) + Energy

What happens if you increase the temp of the reaction? ______

What happens if you decrease the temp of the reaction? ______3. Change in pressure: (gases only with unequal moles) a. Increase of pressure causes the equilibrium to shift toward the side with fewer moles of gas. (It takes up less space.) b. Decrease of pressure causes the equilibrium to shift toward the side with more moles of gas. (It takes up more space.)

3 H2 (g) + N2 (g) ↔ 2 NH3 (g) Moles of gas on reactant side = ______Product side = ______

Increase pressure ______Decrease pressure ______

What effect do the following changes have on the position of equilibrium for this reversible reaction?

PCl5 (g) + Energy ↔ PCl3 (g) + Cl2 (g)

A. Addition of Cl2? ______B. Increase in pressure? ______

C. Removal of energy? ______D. Removal of PCl3? ______

For industrial purposes, we can manipulate equilibrium by changing the temperature, pressure, or concentration of substances to get what is desired or most cost efficient.

______(Ke): Number that relates the amount of reactants to products at equilibrium.

Write the Keq expression for the hypothetical equilibrium described below: aA + bB --- cC +dD

\ Dintrogen tetroxide and nitrogen dioxide are in equilibrium: N2O4(g) ↔ 2 NO2(g)

Write the equilibrium constant expression

Determine Ke at a temp in which [N2O4] = 0.040 M and [NO2] = .20 M

Determine [N2O4] at a temp in which [NO2] = .30 M and Ke = 0.50

Equilibrium Practice Name ______

Conditions for equilibrium 1. Balance between reactants and products. 2. Rate of forward reaction = rate of reverse reaction 3. Closed system (nothing added or removed)

Le Chatelier’s Principle: If a stress is applied to a system in equilibrium, the system will change to relieve the stress. (If a system in equilibrium is subjected to a change, processes occur to counteract that change.) Directions for questions 1-7: Predict the effect of the following changes on their respective equilibrium systems. Answer “shift left”, “shift right” or “no effect”.

+2 +2 1. Cu (light blue) + 4 NH3 (colorless) ↔ Cu(NH3)4 (dark blue) a. Add Cu+2 b. Add NH3 c. Remove NH3

+2 d. Add Cu(NH3)4

2. 2 CO(g) + O2(g) ↔ 2 CO2(g) + heat a. Add CO2 b. Remove O2 c. Add CO d. Add heat e. Remove heat f. Increase pressure g. Decrease pressure

3. N2(g) + 3 H2(g) ↔ 2 NH3(g) + heat a. Remove NH3 b. Add H2 c. Remove N2 d. Add heat e. Cool f. Increase pressure g. Decrease pressure

-2 - -2 + 4. Cr207 (orange) + OH (clear) ↔ 2CrO4 (yellow) + H (clear) a. Add H+ b. Remove OH-

+2 -2 c. Add Ba (which consumes CrO4 )

-2 d. Remove Cr2O7

5. 2 SO3 (g) + CO2 (g) + heat ↔ CS2 (g) + 4 O2 (g)

a. Addition of CO2. b. Addition of CS2. c. Addition of heat. d. Increase in pressure. e. Decrease in pressure. f. Removal of O2. g. Removal of CO2. h. Addition of a catalyst.

6. C (s) + H2O (g) + heat ↔ CO (g) + H2 (g)

a. Decreasing the pressure. b. Increasing the pressure. c. Removing H2. d. Removing H2O. e. Lowering the temperature 7. N2 (g) + 3 H2 (g) ↔ 2 NH3 (g) + heat

a. Removal of H2. b. Addition of a catalyst. c. Addition of heat. d. Increase in pressure. e. This reaction produces ammonia (NH3) and heat energy. If your job was to produce the most ammonia at the least cost, describe 3 things you could do to make more ammonia. Questions 8-9: What effect will the following changes have on the color of the respective equilibrium systems? Iodine gas is blue and nitrogen dioxide gas is red. All other gases in these equations are clear.

8. 2 HI (g) + energy ↔ H2 (g) + I2 (g)

a. decreasing temperature b. increasing temperature c. decreasing pressure d. increasing pressure

9. 2 NO2 (g) ↔ N2O4 (g) + energy

a. decreasing temperature b. increasing temperature c. decreasing pressure d. increasing pressure

10. Hemoglobin carries O2 from the lungs to the rest of the body. When CO is present, CO reacts with the hemoglobin (in place of O2) causing carbon monoxide poisoning. What would be a logical treatment for a person suffering from this poisoning? Why?

Hemoglobin-O2 + CO ↔ Hemoglobin-CO + O2

Equilibrium Problems 1. Sugar is added to a cup of coffee until no more sugar will dissolve. A. Does the addition of another spoonful of sugar increase the rate at which the sugar molecules leave the crystal phase and enter the liquid phase? Explain.

B. Will the sweetness of the solution be increased by this addition? 2. Why are chemical equilibria referred to as “dynamic”?

3. SO2(g) + ½ O2(g) ↔ SO3(g) + 23 kcal A. Discuss conditions that favor a high equilibrium concentration of SO3(g).

B. What mass of oxygen gas is needed to form 1.00 grams of SO3(g)?

4. How does a catalyst affect the equilibrium conditions of a chemical system? Explain.

For questions 5-7; tell whether equilibrium shifts right, left or not at all.

5. CO(g) + NO2(g) ↔ CO2(g) + NO(g) + 54.1 kcal

What happens to this system at equilibrium if: A. the temperature is increased? B. the volume is decreased by a factor of 10?

6. heat + H2O(liq) ↔ H2O(g)

How will the following affect this system in equilibrium? A. reducing volume by increasing pressure B. increasing temperature C. injecting steam in the system (assume no temp change) 7. CO(g) + 2H2(g) ↔ CH3OH(g) + heat

A. the temperature is increased with pressure and amount held constant B. the pressure is increased with temperature and amount held constant

8. Consider the reaction: 4 HCl(g) + O2(g) ↔ 2 H20(g) + 2 Cl2(g) + 27 kcal

What effect would each of the following changes have on the equilibrium concentration of Cl2(g)? (Answer decrease, increase or no effect)?

A. Increasing the temperature of the reaction vessel.

B. Decreasing the total pressure.

C. Increasing the concentration of O2(g).

D. Increasing the volume of the reaction chamber.

E. Adding a catalyst.

9. Nitric oxide gas (NO) releases 13.5 kcal/mol when it reacts with oxygen gas to produce nitrogen dioxide gas. A. Write a balanced equation for this reaction. Include the energy term.

B. What effect will raising the temperature have on: 1. the equilibrium concentration of: a. NO(g) b. O2(g) c. NO2(g)

2. the numerical value of the equilibrium constant 3. the speed of formation of NO2(g)

C. What effect will increasing the concentration of NO(g) have on: 1. the equilibrium concentration of: a. O2(g) b. NO2(g)

2. the numerical value of the equilibrium constant 3. the speed of formation of NO2(g)

10. Write the equilibrium law expression for the following reactions: A. N2(g) + 3 H2(g) ↔ 2 NH3(g)

B. CO(g) + NO2(g) ↔ CO2(g) + NO(g)

+ +2 C. Zn(s) + 2 Ag (aq) ↔ Zn (aq) + 2 Ag(s)

+2 - D. PbI2(s) ↔ Pb (aq) + 2 I (aq)

- - E. CN (aq) + H2O (liq) ↔ HCN(aq) + OH (aq) 11. Write the equilibrium law expression for the following reactions: A. C2H6(g) ↔ H2(g) + C2H4(g)

+2 +2 B. Cu (aq) + 4 NH3(aq) ↔ Cu(NH3)4 (aq)

+ - C. Ag (aq) + Cl (aq) ↔ AgCl(s)

+ +2 - D. PbSO4(s) + H (aq) ↔ Pb (aq) + HSO4 (aq) E. CO(g) + 1/2 O2(g) ↔ CO2(g) + heat

12. Determine the value of the equilibrium constant (Ke) for the reaction at 448ºC: 2 HI(g) ↔ H2(g) + I2(g)

At 448ºC, the concentrations of the gases at equilibrium are: HI = 4.0 x 10-3 M -3 H2 = 7.5 x 10 M -5 I2 = 4.3 x 10 M