Unit 7: Equilibrium.

7.1 Introduction to 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.

7.2 Direction of Reversible Reactions.

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?

7.3 Reaction Quotient and Equilibrium Constant.

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.

7.4 Calculating the Equilibrium Constant.

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 Kp for the reaction 3O2 ⇌ 2O3 if equilibrium partial pressures are 0.998atm and 0.002 respectively.

7.5 Magnitude of the Equilibrium Constant.

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), KC=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?

7.6 Properties of the Equilibrium Constant.

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)

7.7 Calculating Equilibrium Concentrations.

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=10

7.8 Representations of Equilibrium.

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.

    7.9 Introduction to Le Châtelier’s Principle.

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

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

    7.10 Reaction Quotient and Le Châtelier’s Principle.

    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.

    7.11 Introduction to Solubility.

    Write the Ksp expression for the dissolution of a salt.

    Calculate the solubility of a salt from the Ksp value.

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

    7.12 Common-Ion Effect.

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

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

    Use Ksp expressions to calculate this impact quantitatively.

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