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Community College of Philadelphia Department of Chemistry CHEM 101 Distance Course Laboratory Report Sheet Name: Date: Email: Laboratory Instructor: Course Nbr.: CHEM 101 Distance Section: Experiment Nbr.: D – Home-based Lab Experiment Title: Le Chatelier’s Principle Purpose: Concepts related to the textbook: Conclusion: M. O’Connor 6/24/2020 Experiment D – Le Chatelier’s Principle Experiment D deals with the concepts of equilibriums and Le Chatelier’s Principle. In this activity you will complete several tables using the concepts of Le Chatelier’s Principle. Read over the background information below and Chapter 6 Sections 5 & 6 in the textbook for additional information and clarification. Also watch the included YouTube videos for more examples of equilibriums and Le Chatelier’s Principle. Once you understand these equilibrium concepts, complete the activity included at the end of this document. (A file containing just the activity is included on Canvas as well.) If you have any questions, please feel free to contact me through Canvas. Good luck! -MAO (assignment adapted from https://www.lcps.org/cms/lib/VA01000195/Centricity/Domain/16570/Le\%20Chateliers\%20Principle\%20Worksheet.pdf and http://butane.chem.uiuc.edu/cyerkes/Chem102AE_Fa08/homepage/Chem102AEFa07/worksheets/Worksheet\%2019.pdf) Background Information Video 1 – Explanation of Le Chatelier’s Principle: https://www.youtube.com/watch?v=XmgRRmxS3is Video 2 – Short Le Chatelier’s Principle Experiment: https://www.youtube.com/watch?v=ZQk_KqW4U8A A reversible reaction is one that can occur in either direction. The forward reaction proceeds to the right, while the reverse reaction proceeds to the left. We represent this in a chemical equation by using a double headed arrow (⇌). When the rate of the forward and the reverse reactions are equal, then we say that the reaction is at equilibrium. This means that the net concentrations of the reactants and products do not change at equilibrium, even though both the forward and reverse reactions are still occurring. Le Chatelier’s Principle states that if a stress is applied to a system at equilibrium, the system will adjust to partially relieve the stress and reach a new state of equilibrium. Some stresses that can be applied to the system include changes in concentration, pressure, and temperature. Let’s look at these stresses on a generic chemical equation. Please note, only gases and aqueous substances will have an effect on the equilibrium. Changes in pure solids and pure liquids will have no effect! A (g) + B (g) ⇌ C (g) + D (s) + heat 1. Changes in Concentration – changing the concentration of either reactants or products will shift the reaction to the right, to the left, or leave it unchanged. a. Adding more reactant or product will drive the equilibrium in the direction needed to use up some of the excess substance i. Adding more A or B in the above equilibrium will drive the forward process (shift the reaction to the right). ii. Adding more C in the above equilibrium will drive the reverse process (shift the reaction to the left). (notice that changes to D will have no effect since it is a pure solid) b. Removing a reactant or product will shift the equilibrium in the direction needed to produce more of the substance that was removed i. Removing A or B in the above equilibrium will shift the reaction to the left. ii. Removing C in the above equilibrium will shift the reaction to the right. 2. Changes in Temperature – changes in temperature can be quite complicated in equilibriums, however we can simplify this process by treating heat as a reactant or a product in our equilibrium equation. If the reaction is exothermic, heat is produced and can be thought of as a product. If the reaction is endothermic, heat is absorbed and can be thought of as a reactant. Now the equilibrium rules for changes in concentration will apply to changes in temperature! a. Raising the temperature of a reaction can be thought of as adding heat, and the reaction will shift to the side that uses up the excess heat. Endothermic reactions (heat = reactant) will shift to the right. Exothermic reactions (heat = product) will shift to the left. i. The above reaction is exothermic, therefore adding heat shifts the reaction to the left. b. Lowering the temperature of a reaction can be thought of as removing heat, and the reaction will shift to the side that produces heat. Endothermic reactions (heat = reactant) will shift to the left. Exothermic reactions (heat = product) will shift to the right. i. The above reaction is exothermic, therefore removing heat shifts the reaction to the right. 3. Changes in Pressure – increasing or decreasing the pressure on an equilibrium system involving gases will cause the reaction to shift to the right, to the left, or leave it unchanged. a. Increasing the pressure will cause the equilibrium to shift to the side with fewer moles of gas. Gas pressure decreases as the amount of gas decreases (i.e. they are directly proportional). i. In the above reaction, there are 2 moles of gas on the reactant side (A & B), and 1 mole of gas on the product side (C). The reaction will shift to the side with few moles of gas, in this case the product side (shift to the right). b. Decreasing the pressure will cause the equilibrium to shift to the side that has more moles of gas. Gas pressure increases as the amount of gas increases. i. In the above reaction, there are 2 moles of gas on the reactant side (A & B), and 1 mole of gas on the product side (C). The reaction will shift to the side with more moles of gas, in this case the reactant side (shift to the left). Experiment D – Le Chatelier’s Principle Worksheet M. O’Connor 6/24/2020 Student Name ____________________________________________________ Now that we have a better understanding of equilibriums and Le Chatelier’s Principle, let’s complete the tables on the following pages. Each table references an equilibrium reaction, and presents different stresses to that system. Write left, right, or none for how the equilibrium shifts under the stress, and write decreases, increases, or remains the same for how the concentrations of reactants and products will change. Reaction 1: Stress Equilibrium Shift [N2] [H2] [NH3] 1. Add N2 Right ---------- Decreases Increases 2. Add H2 ---------- 3. Add NH3 ---------- 4. Remove N2 ---------- 5. Remove H2 ---------- 6. Remove NH3 ---------- 7. Increase Temperature 8. Decrease Temperature 9. Increase Pressure 10. Decrease Pressure Reaction 2: Stress Equilibrium Shift [H2] [I2] [HI] 1. Add H2 ---------- 2. Add I2 ---------- 3. Add HI ---------- 4. Remove H2 ---------- 5. Remove I2 ---------- 6. Remove HI ---------- 7. Increase Temperature 8. Decrease Temperature 9. Increase Pressure 10. Decrease Pressure Reaction 3: Stress Equilibrium Shift Amount NaOH (s) [Na+] [OH-] 1. Add NaOH (s) ---------- 2. Add NaCl (adds Na+ ion) ---------- 3. Add KOH (adds OH- ion) ---------- 4. Add H+ (removes OH-) ---------- 5. Increase Temperature 6. Decrease Temperature 7. Increase Pressure 8. Decrease Pressure