Unit 7: Equilibrium.

Describe characteristics of equilibrium, both macroscopically and at the particle level.

1. What does it look like macroscopically when a chemical system is at equilibrium?
2. Explain equilibrium at the particle level in terms of reaction rates.

Identify the point at which equilibrium has been reached on a graph of amount or rate vs. time.

1. Explain equilibrium at the particle level in terms of reaction rates.
2. Explain what it means when the forward and reverse rates become constant on a rate vs. time graph.

Determine if the forward rate or reverse rate is faster (or if they are the same) based on the direction of a reaction.

1. Given a reaction moving in a certain direction, how can you tell which rate is faster?
2. At equilibrium, how do the forward and reverse rates compare?

Write K and Q expressions for a reversible reaction.

1. Write the equilibrium expression in terms of partial pressures for N₂(g) + 3H₂(g) ⇌ 2NH₃(g) .
2. The reaction A(aq) + 2B(aq) ⇌ 2C(s) + D(aq) has not yet reached equilibrium. Write the appropriate reaction quotient or equilibrium expression.
3. Explain the difference between Q and K.

Calculate the value of K given equilibrium conditions (in concentration or pressure).

1. Determine the value of the equilibrium constant Kc for the reaction H₂ + I₂ ⇌ 2HI. If the equilibirum concentration of H₂ and I₂ are 0.1M and the equilibirum concentration of HI is 1.0M
2. Calculate K_p for the reaction 3O₂ ⇌ 2O₃ if equilibrium partial pressures are 0.998atm and 0.002 respectively.

Recognize systems that essentially go to completion or barely proceed at all by examining the magnitude of K values.

1. Explain why the equilibrium concentration of A and B are essentially 0.0M for the reaction A(aq) + B(aq) ⇌ C(s) + D(aq), K_C=1x10⁷ if 1.0M of A and B are allowed to react.
2. What does a very small K value tell you about a reaction’s progress?

Manipulate the value of K to correspond to a manipulation of the reaction it represents.

1. If the reaction A(aq) + B(aq) ⇌ C(s) + D(aq) with K=10 determine the value of K of the reaction C(s) + D(aq) ⇌ A(aq) + B(aq)
2. If the reaction A(aq) + B(aq) ⇌ C(s) + D(aq) with K=10 determine the value of K of the reaction 2A(aq) + 2B(aq) ⇌ 2C(s) + 2D(aq)

Use ICE tables and comparisons of Q vs K to determine equilibrium concentrations/pressures.

1. Determine the equilibrium concentration of A and D when 1.0M of A and B are allowed to react according to the reaction A(aq) + B(aq) ⇌ C(s) + D(aq) with K_eq=10

Draw or complete a particle diagram to represent the relative numbers at equilibrium, or evaluate a diagram to calculate the value of K for a represented system.

1. Draw a particle diagram with 10 total particles for the theoretical reaction: 2A(g) + B₂(g) ⇌ 2AB(g) with K_eq=1.0

Use Le Châtelier’s Principle to determine the shift in a system in response to a stress.

1. If the reaction A(g) + B(aq) ⇌ C(aq) + D(aq) is at equilibrium the total volume of the container is made smaller with q piston at constant temperature. Will the reaction shift to the left or to the right?

Describe the change in physical properties after a system responds to stress (color, temperature, etc.).

1. NO₂ is dark brown and N₂O₄ is colourless. They form the exothermic equilibrium reaction 2NO₂ ⇌ N₂O₄ + heat. Justify whether the reaction mixture will become a lighter or darker brown when the temperature of reaction vessel is increased.

Evaluate Q vs K to determine the direction in which a reaction will proceed to reestablish equilibrium.

Determine if a stress will change the value of Q or K.

1. A exothermic reaction is at equilibrium with a K_eq = 10.0. The reaction container is increased from 25^oC to 50^oC. Justify whether K_eq will be less than, equal to, or greater than 10.0 When the reaction returns to equilibrium.
2. A exothermic reaction is at equilibrium with a K_eq = 10.0. Additional reactant is added to the reaction vessel. Justify whether K_eq will be less than, equal to, or greater than 10.0 When the reaction returns to equilibrium.

Write the Ksp expression for the dissolution of a salt.

1. Write the K_sp expression for the dissolution of NaCl
2. Write the K_sp expression for the dissolution of BaCl₂
3. Write the K_sp expression for the dissolution of NaCH₃COO

Calculate the molar solubility of a salt from the Ksp value.

1. The K_sp of Ca(OH)₂ is 1.3x10^-6. Determine its molar solubility (M).

Determine if a salt is considered soluble by examining its Ksp value.

1. Does a large K_sp imply a salt is soluble or insoluble?

Evaluate a system to determine if a common ion will impact the solubility of a salt.

1. Explain whether additional NaCl(s) will precipitate from a saturated solution of NaCl(aq) if NaBr(s) is added.
2. Explain whether additional NaCl(s) will precipitate from a saturated solution of NaCl(aq) if KBr(s) is added.

Use Le Châtelier’s principle to discuss this impact qualitatively.

1. Write the reaction for the dissolution of NaCl. Then describe the direction of shift if NaBr(s) is added.

Use Ksp expressions to calculate this impact quantitatively.

1. Compare K and Q for the dissolution of NaCl both before and after NaBr(s) is added to a saturated solution.