Catalyst

Cobalt (II) Chloride EquilibriumCo(H2O)6

2+(aq) + 4Cl-(aq) ⇌ CoCl42-(aq) + 6H2O(l)

(Think-Write): According to LC’s Principle, why do you think the color changed?(Pair): Find out what your partner thinks(Share): Share your findings with the class.

Lecture 8.7 – Le Châtelier’s Principle II

Learning Targets LT 8.7 – I can define Le Châtelier’s principle and use this principle to predict how

concentration, temperature, and pressure will impact a given equilibrium. I can explain why the equilibrium shifts in a 3-5 sentence justification paragraph.

LT 8.8 – I can write an equilibrium constant (Keq) for a given chemical reaction, describe the significance of this value for a chemical reaction, and calculate the Keq for an equilibrium reaction.

Common Core Standards

• CCSS.ELA-L.RST.11-12.3: Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.

• CCSS.ELA-L.RST.11-12.4: Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11–12 texts and topics.

• CCSS.ELA-L.RST.11-12.9: Synthesize information from a range of sources (e.g., texts, experiments, simulations) into a coherent understanding of a process, phenomenon, or concept, resolving conflicting information when possible.

Where are we going?Real-world applications College-level work

What is an equilibrium constant?

I. Equilibrium Constants (Keq)

A. Equilibrium constant (Keq): the ratio of the product concentrations to reactant concentrations at eq.

1. Only written for aqueous (aq) and gaseous (g) substances

B. For the general reaction:aA (aq) + bB (aq) cC (aq) + dD (aq)⇌

The equilibrium constant (Keq):

8.8: I can write an equilibrium constant for a given chemical reaction…

Class Example (I Do)Write the equilibrium constant for the following equilibrium:

2NO (g) + Cl2 (g) 2NOCl (g)⇌

8.8: I can write an equilibrium constant for a given chemical reaction…

Class Example (We Do)Write the equilibrium constant for the following equilibrium:

Ag (s) + 2 NH3 (aq) ⇌ Ag(NH3)2+ (aq)

8.8: I can write an equilibrium constant for a given chemical reaction…

How do we calculate Keq?

II. Calculating Keq

A. Magnitude of K1. Keq > 1: Products favored at equilibrium

2. Keq < 1: Reactants favored at equilibrium.

B. LC’s Principle and Keq

1. Keq > 1: Eq. lies to right

2. Keq < 1: Eq. lies to left

8.8: I can…describe the significance of Keq for a chemical reaction…

Class Example (I Do)N2(g) + 3H2(g) ⇌ 2NH3(g)

1. Write the equilibrium constant:

• Solve for Keq if [NH3] = 0.933M, [N2] = 0.533M, [H2] = 1.600M:

• State whether reactants or products are favored.

8.8: I can…calculate Keq for a chemical reaction.

Class Example (We Do)PCl5(g) PCl⇌ 3(g) + Cl2(g)

1. Write the equilibrium constant:

• Solve for Keq if [PCl5] = 0.135M, [PCl3] = 0.55M, [Cl2] = 0.40M

• State whether reactants or products are favored.

8.8: I can…calculate Keq for a chemical reaction.

Whiteboard Question #1

• Write the equilibrium constant expressions for the following equilibrium reactions:a) 2N2H4(g) + 2NO2 (g) 3N⇌ 2(g) + 4H2O(g)

a) 2NaHCO3(s) Na⇌ 2CO3(s) + H2O(g) + CO2(g)

Whiteboard Question #2H2 + Cl2 2HCl⇌

1.Write the equilibrium constant expression.

2.Solve for Keq if [HCl] = 2.0M, [Cl2] = 1M, [H2] = 0.5M

3.State whether reactants or products are favored.

Whiteboard Question #3C6H6(l) C⇌ 6H6(g)

1.Write the equilibrium constant expression.

2.Solve for Keq if [C6H6(g)] = 0.00334M:

3.State whether reactants or products are favored.

2-4-6-10 Practice

• Goal: Achieve a minimum of 10 points• Work with me if you are still at a “1”.• Complete all of the problems for a prize!• 15 minutes starts now!

Lab 8.2: Le Châtelier’s Principle

Co(H2O)62+(aq) + 4Cl-(aq) ⇌ CoCl4

2-(aq) + 6H2O(l)Purpose: predict the changes observed in an equilibrium system involving cobalt complexes and explain these changes in terms of Le Châtelier’s Principle.Lab Jobs:

1. Materials manager – gets materials, safety2. Facilitator/leader – facilitates discussion/on task behavior3. Timekeeper – records time, ensures on task behavior4. Recorder – records data

Materials, safety, data.

CCSS: Follow precisely a complex multistep procedure when carrying out experiments...

Lab Groups (P.4)

• Group 1: Cesar, Erick, Manny, Adrian• Group 2: Ricardo, Alexia, Carla, Pedro• Group 3: Steven, Marco, Cindy, Kim M.• Group 4: Kim P., Akemy, Melissa• Group 5: Michelle, Melly, Andrea, Melany• Group 6: Madelin, Stephanie, Laura, Jocelyn• Group 7: Marvin, Pablo, Alexis, Christian• Group 8: Neyda, Karla, Maria, Donna

Lab Debrief

• In your journal, please write a short (1-3 paragraphs) well-organized mini-essay addressing the following questions:1. What is dynamic equilibrium?2. What does Le Châtelier’s Principle state and how is it

related to equilibrium?3. What reaction was studied? How did the lab illustrate Le

Châtelier’s Principle? What stresses were applied and how did the equilibrium respond?

4. What evidence did the lab provide for how the equilibrium shifted? Give examples and be specific!

CCSS: Synthesize information into a coherent understanding of a process, phenomenon, or concept…

Mr. Aldredge’s Paragraph

“Dynamic equilibrium is the state of a chemical equilibrium in which the rates of the forward and reverse reactions are equal. In the lab activity, the equilibrium between Co(H2O)6

2+ and CoCl42+

was studied. Various stresses were applied to this equilibrium, such as increasing or decreasing the temperature and adding or removing products and reactants. The evidence for the observed shifts in equilibrium was a change in color between the cobalt compound from blue to pink or vice versa. The lab is connected to the idea of the equilibrium constant, Keq, because if Keq > 1 the equilibrium lies to the right, and if Keq < 1 the equilibrium lies to the left. Therefore, based on the color of the reaction mixture we can conjecture if Keq is greater than or less than 1.”

Learning Targets LT 8.7 – I can define Le Châtelier’s principle and use this principle to predict how

concentration, temperature, and pressure will impact a given equilibrium. I can explain why the equilibrium shifts in a 3-5 sentence justification paragraph.

LT 8.8 – I can write an equilibrium constant (Keq) for a given chemical reaction, describe the significance of this value for a chemical reaction, and calculate the Keq for an equilibrium reaction.

Learning Target Log Update

Update your LT Log for LT’s 8.7-8.8 (self-assessment)

• Homework: Finish lab analysis if not done• Unit 8 Test Thursday/Friday

Closing Time