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A topic from the subject of Analysis in Chemistry.

  • 11 months ago
  • 6 min read

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Equilibrium: Le Chatelier's principle
Overview:
Le Chatelier's principle is a useful tool to predict how a chemical equilibrium will shift when the conditions of the system are changed. It states that if a stress is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.
Key Points:

  • Adding or removing reactants or products: If more reactants are added to the system, the equilibrium will shift to form more products. If more products are added, the equilibrium will shift to form more reactants.
  • Changing the temperature: If the temperature is increased, the equilibrium will shift in the direction that is endothermnic (requires heat). If the temperature is decreased, the equilibrium will shift in the direction that is exothermnic (releases heat).
  • Changing the pressure: If the pressure is increased on a system that involves gases, the equilibrium will shift to the side with fewer moles of gas. If the pressure is decreased, the equilibrium will shift to the side with more moles of gas.
  • Adding a catalyst: A catalyst speeds up the rate of both the forward and reverse reactions, but it does not affect the equilibrium position.

Main Concepts:
Le Chatelier's principle is a qualitative tool that can be used to predict the direction of a shift in equilibrium. The principle is based on the idea that a system in equilibrium will always try to minimize the stress that is applied to it.
* Le Chatelier's principle can be used to predict the effects of changing the temperature, pressure, concentration of reactants or products, or adding a catalyst to a system in equilibrium.
Experiment: Equilibrium: Le Chatelier's Principle

Purpose: To demonstrate the effects of changes in concentration, temperature, volume, and surface area on chemical equilibrium.


Materials:


  • Cobalt(II) chloride hexahydrate (CoCl2·6H2O)
  • Deionized water
  • Test tubes
  • Thermometer
  • Graduated cylinder
  • Beaker


Procedure:

  1. Change in concentration:

    1. Dissolve approximately 0.5 g of CoCl2·6H2O in 10 mL of deionized water.
    2. Prepare three additional test tubes with the same solution, but adjust the concentrations to 0.25 g, 0.125 g, and 0.0625 g respectively.
    3. Observe the colors of the solutions and record your observations.

  2. Change in temperature:

    1. Prepare a solution of CoCl2·6H2O in deionized water at a concentration of 0.5 g/10 mL.
    2. Place the test tube in a beaker of hot water and observe the color changes.
    3. Remove the test tube from the hot water and place it in a beaker of cold water. Observe the color changes.

  3. Change in volume:

    1. Prepare a solution of CoCl2·6H2O in deionized water at a concentration of 0.5 g/10 mL.
    2. Transfer 5 mL of the solution to a test tube.
    3. Add 5 mL of deionized water to the test tube. Observe the color changes.

  4. Change in surface area:

    1. Prepare a solution of CoCl2·6H2O in deionized water at a concentration of 0.5 g/10 mL.
    2. Crush a small crystal of CoCl2·6H2O into a powder.
    3. Add the powdered CoCl2·6H2O to the solution and observe the color changes.


Observations:

  • Change in concentration: The color of the solution becomes more intense as the concentration increases.
  • Change in temperature: The color of the solution changes from pink to blue when heated and back to pink when cooled.
  • Change in volume: The color of the solution becomes less intense as the volume increases.
  • Change in surface area: The color of the solution changes more rapidly when the surface area of the solid is increased.

Significance:

This experiment demonstrates the effects of changes in concentration, temperature, volume, and surface area on chemical equilibrium. Le Chatelier's principle states that if a change in conditions is applied to a system at equilibrium, the system will shift in a direction that counteracts the change. By understanding the effects of these changes, we can manipulate chemical reactions to obtain desired outcomes.


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