You need to have your dried flowers by Monday, October 3. It is my intention to stay late on Mondays and Wednesdays (to 3:15 or 3:30 as needed) so that you can carry out your IA investigations. I still have not received any rough drafts or background research from either of you, and the FINAL paper is due November 1st. A failure to complete the IA results in you not getting a diploma. You've known about this since before Singapore.
Textbook: Chapter 7
Links: IB Chemistry Home Notes
1. Practicing problem solving using Le Chatelier's Principle
2. Discussion of the Haber Process
Lesson Objectives: You should be able to:
1. Explain Le Chatelier's Principle in your own words.
2. Explain what it means when reactions must shift either to the left or the right.
3. Describe the effects of changing concentration, temperature and pressure on reactions at equilibrium.
4. Describe what happens when a catalyst is added to a reaction at equilibrium.
5. Explain what the Haber Process and the Contact Process is, and their significance.
Mission 1: Le Chatelier's Principle, Part Deux. We talked about Le Chat last week. Basically, if there is a disturbance in equilibrium, the reaction shifts in response to re-establish equilibrium in such a way to minimize the effect of the change.
Change in concentration. When an increase in concentration of a reactant occurs and disrupts equilibrium, the rate of the forward reaction will increase. The reverse reaction does not change, so the rates are no longer equal. When equlibrium is re-established, the mixture will have new concentrations and the equlibrium will have shifted to the right to favor the products. Addition of reactant causes the system to respond by removing reactant to make more product, which favors the forward reaction.
Change in pressure. Equlibrium involving gases will be affected by a change in pressure if the reaction involves a change in the number of molecules. If a reaction at equilibrium is subject to an increase in pressure, the system responds by favoring the side with the smaller number of molecules. A decrease in pressure will cause a shift to the side with the larger number of molecules. As long as the temperature remains the same, Kc will be unchanged.
Change in temperature. Kc is temperature-sensitive, so it changes as temperature changes. Exothermic reactions (delta-H negative) release energy and endothermic reactions (delta-H positive) absorb energy. A negative delta-H means that the forward reaction is exothermic. If this reaction is subjected to a temperature decrease, the system responds by producing heat and favoring the forward reaction. Equilibrium shifts to to the right as a result. This means more product is formed. A new equilibrium is achieved and Kc changes.
Increasing the temperature favors the reverse reaction and shifts equilibrium to the left, decreasing the value of Kc and reducing the amount of product formed.
Adding catalysts. Catalysts speed up reactions by reducing Ea. The rate of both reactions will increase by the same factor, which has no effect on the equilibrium position. Adding a catalyst reduces the time it takes to achieve equilibrium.
Page 231 provides a nice summary table.
Mission 2: Large Scale Industrial Stuff. The following video describes the Haber Process for ammonia production.
The Contact Process is the production of sulfuric acid. It is composed of three simple reactions: the combustion of sulfur to form sulfur dioxide, the oxidation of sulfur dioxide to sulfur trioxide, and the combination of sulfur trioxide with water to produce sulfuric acid. The overall rate depends on step 2; the oxidation of SO2 to SO3. Similar to the Haber process, one can predict the condition that will favor the formation of product. Page 234 has a nice, neat summary table that you should reference.
Homework: Read up on the production of methanol on page 235. Good practice problems are on pages 232, 235 and 236-7.