Overview of Le Chatelier Principle for Science Class

This experiment entitled "Chemical Equilibrium" aims to help students to investigate the effects of concentration and temperature upon the position of equilibrium in a cobalt chloride solution, Co(H2O)62+. In this experiment, cobalt crystal is dissolved with distilled water and ethanol which the initial colour is purple-pinkish and a few drops of concentration of HCl is added to the test tube, the final colour is in deep blue colour. Upon the effect of concentration and temperature, the equilibrium will shift backward in the reaction with accordance with Le Chatelier's principle producing more HCl molecules.

This means that equilibrium rate of forward and backward reactions were met. In result, this reaction is endothermic. Introduction

Chemical equilibrium is the state in which a chemical reaction proceeds at the same rate as its reverse reaction; the rate of forward and reverse reaction are equal, and the concentration of the reactants and products stop changing1. When this condition was met, there was no change in the proportions of the various compounds involved, and the reaction ceases to progress.

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The equilibrium state has a dynamic – that is, active – nature being characterized by the simultaneous and continuous formation of products from the reactants and reactants from the products2. But these simultaneous reactions do not necessarily follow that the concentrations of the reactants is equal to that of the product(s). Instead, the ratio of the concentrations of the reactants to the concentration of the product(s) raised to their coefficient in the balanced equation is Keq, a constant.

Taking the Le Chatelier’s principle into consideration, there are factors that may shift or influence the position of equilibrium4. The Le Chatelier’s principle states that if stress is applied to a system at equilibrium, the equilibrium will tend to shift in the direction which will relieve the applied stress. Some factors that can affect are concentration, temperature
and pressure. Alterations in the system’s conditions at equilibrium may favour either a forward or backward shift.

The objectives of the experiment are: to evaluate how the change in concentration and the change in temperature affect the equilibrium system, to explain the effects of these changes in the equilibrium system, and to interpret the results based on the Le Chatelier’s principle.

Experiment

Materials & Equipments:

• 3 Test tubes
• Cold water bath
• Concentrated HCl
• 60mL of Ethanol
• Cobalt (II) Chloride crystal
• Silver Nitrate (AgNO3)
• H2O, distilled water

Changes in color (specifically intensity), appearances and reactions should be observed and taken note of throughout the experiment. To begin this experiment, cobalt (II) chloride crystal is added into a new test tube and dissolve it with distilled water. Make sure the solution is mixed well before adding concentration of HCl. Continuously adding drops of concentration of HCl into the test tube until the solution turns deep blue in colour. After that, separate the new solution to 2 new test tube.

Test tube 1 is placed into a cold water bath to analyse the final colour of the solution when it encounters cool surrounding. Silver nitrate (AgNO3) is added into test tube 2 and is mixed well. Observations were recorded, and direction of shift was deduced from the observations. If the reagent caused the mixture to shift to a lighter colour, then the direction of shift is backward. If the reagent caused the mixture to shift to a darker colour, then the direction of shift is forward.