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Chemistry

Chemistry 15: 5-6

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WebLecture

Disturbing Chemical Equilibrium

Chapter 15: 5-6 Homework

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 15: Sections 5 and 6.

Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 15: Sections 5-6.

Study Notes
  1. 15.5 In many analyses, we recognize that an overall reaction is a sequence of steps. We may need to multiply a reaction's coefficients or reverse it to achieve the net desired overall reaction. These manipulations affect the equilibrium constant of the reaction step.
    • Changing the stoichiometric coefficients by multiplying through a reaction equation will change the equilibrium constant by an exponential factor. For example, if we double the reaction coefficients, the equilibrium constant will be squared.
    • If we reverse a chemical reaction, the products and reactants switch places in the ratio for the equilibrium constant. The equilibrium constant for a reverse reaction is the inverse of the forward reaction equilibrium constant: Kreverse = 1 / Kforward.
  2. 15.6 If a system at equilibrium is disturbed, it will try to establish a new equilibrium by mitigating the effect of the disturbance as much as possible. A disturbance could include changes in temperature, the addition of a reactant or product, or in gases, changes in volume.

Key Formula

Doubling a reaction K 2   =   K 1 2
Reversing a Reaction K 2   =   1 K 1
Adding Two Reactions K net   = K 1     K 2  

Web Lecture

Read the following weblecture before chat: Disturbing an Equilibrium State

Study Activity

Videos for Chapter 15: Principles of Chemical Reactivity: Equilibria

Review the Videos at Thinkwell Video Lessons.

  • Under "Chemical Equilibrium"
    • Shifting Chemical Equilibrium
      • Le Chatelier's Principle
      • The Effect of Changing Amounts on Equilibrium
      • The Effect of Pressure and Volume on Equilibrium
      • The Effect of Temperature and Catalysts on Equilibrium

Follow the instructions at ChemReaX Virtual Lab: Le Chatelier's Principle for the hydrogen iodide synthesis reaction.

  • Set up the reaction on the General Reactions page by selecting the reaction from the General Reactions list; this should set the initial composition to the right bar values. Note the default pressure factor at 1.0.
  • Run the reaction and record the composition of the simulated final state.
  • Change the pressure factor to 0.5 and rerun the reaction. What happens to the values in the final state?
  • Change the pressure factor to 2.5 and rerun the reaction. What happens to the values in the final state?
  • Change the pressure factor to 5.0 and rerun the reaction. What happens to the values in the final state?

Chat Preparation Activities

Chapter Quiz


(Aligns to) AP #12 GUIDED INQUIRY — Determining the rate law — Phase II

Run the experiment you designed in Phase I at least twice at different temperatures, and at least twice at different concentrations. Analyze your data, and predict what will happen if you increase or decrease temperature, and increase or decrease one of the reactants. Test your predictions by doing a third run for each change.

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