Le Châtelier

Le Châtelier’s principle states that The system will have one reaction dominate until the offsetting changes allow the rates of the forward and reverse reactions to be equal again (reestablishing equilibrium). If the forward reaction dominates in order to offset the changes, we say the system “shifts to the right” or “shifts toward products” in order to reestablish equilibrium conditions. This will increase the concentration of the products and decrease the concentration of the reactants. However, if the reverse reaction dominates in order to offset the changes, we say the system “shifts to the left” or “shifts toward reactants” to reestablish equilibrium conditions. This will increase the concentrations of the reactants and decrease the
Again by observing changes in the color and by monitoring the absorbance of the system resulting from placing a stress on the system we can monitor the equilibrium of the system. For each of the two systems you will make observations of the results from stresses placed on each system, and use the information you collect to determine whether the reaction in each system is endothermic or exothermic.

Procedure: Begin by setting up a hot water bath using a 250 mL beaker. The water does not have to reach boiling, but it should be hot. Set up an ice water bath in a 150 mL beaker by filling the beaker about 2/3 full with ice and adding about 25 mL water. For each experiment (Part I and Part II), each group of students working together should assemble 6 clean test tubes (15 × 125 mm) and 2 clean Spec- 20 cuvettes.

Part I: Fe(NO3)3 + KSCN Equilibrium
1. Using a 100 mL graduated cylinder, transfer 50 mL of 0.002 M KSCN into a clean 100 or 150 mL beaker. Observe any color in the solution. Using a disposable pipet, add 4 drops of 0.2 M Fe(NO3)3 to the solution in the beaker and mix well. Observe the color of the solution. This is your equilibrium solution as described by eq. 1