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Chemistry 15: 1-2

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Chemical Equilibrium

Chapter 15: 1-2 Homework

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 15: Sections 1 and 2.

Study Notes

Key Formula

Rules for Reaction Rates
In a solution, the reaction quotient has the form

aA + aB → cC + dD Q   =   [ C ] c [ D ] d [ A ] a [ B ] b

Note that the stoichiometric coefficient becomes the exponent on the concentration of the associated molecule, and that the concentration of water, when it is a reactant or product, is usually ignored.

If a solid is involved, the concentration of the solid is [S] = 1. It can effectively be ignored: the amount of a solid does not affect the reaction quotient or equilibrium constant.
If the reaction is between gases, then the concentrations of the gas can also be presented by the partial pressures of the gas:

A (g) + B(g) ↔ 2 C(g)

Kp = PC2 / (PA*PB)

The value of the equilibrium constant can tell us whether the reaction is product-favored or reactant-favored at equilibrium.

If K > 1, the reaction is product-favored: the product concentrations will be greater than the reactant concentrations at equilibrium.

If K < 1, the reaction is reactant-favored: the reactant concentrations will be greater than the product concentrations at equilibrium.

The value of the reaction quotient at any time, compared to the equilibrium constant (which is just the reaction quotient at equilibrium) can tell us which way the reaction is running.

If Q < K: the reaction must run forward to decrease the amount of reactants and increase the amount of products so that Q → K.

If Q > K: the reaction must run backwards to decrease the amount of products and increase the amount of reactants so that Q → K.

If Q = K: the reaction is in equilibrium.

Web Lecture

Read the following weblecture before chat: The Equilibrium Condition

Study Activity

Videos for Chapter 15: Principles of Chemical Reactivity: Equilibria

Review the Videos at Thinkwell Video Lessons.

  • Under "Chemical Equilibrium"
    • Principles of Chemical Equilibrium
      • The Concept of Equilibrium
      • The Law of Mass Action and Types of Equilibrium
      • Converting Between Kc and Kp
    • Using Equilibrium Constants
      • Approaching Chemical Equilibrium
      • Predicting the Direction of a Reaction

Use the Virtual Lab at the Chem Collective Cobalt Chloride and LeChatlier's Principle. If the lab does not load, try refreshing your browser window.

  1. Click on the "Cobalt Lab" link in the upper right and follow the instructions in the assignment to work through the lab.
  2. What happens as you change the temperature? How the the solution re-establish its equilibrium state?
  3. Note that if you have Java installed, you can download the lab and run it locally.

Chat Preparation Activities

Chapter Quiz

(Aligns to) AP #11 GUIDED INQUIRY — Titration Methods — Phase III

Repeat your experiment if necessary to confirm your results, then submit your formal report.