Applications of Lechatelier’s Principle

Purpose:

The purpose of this lab experiment is to observe systems at equilibrium, and to determine what happens when stresses are applied to such systems. Most chemical reactions are reversible. When the reaction is at equilibrium, the forward and reverse rate are equal. However, when disturbed the rates of the reaction changes.

Materials:

Hot plate

Water

Ice

Beakers, 3

Marker

Petri dish

Test tubes, 2

Test tube holder

Test tube rack

Pipet, Beral-type

Graduated cylinder, 50-mL

Iron(III) nitrate solution, Fe(NO3)3 ,0.2M, 4 drops

Potassium nitrate, KNO3, 0.5g

Potassium thiocyanate, KSCN, 0.5g

Potassium thiocyanate solution, KSCN, 0.002 M, 20 mL

Sodium phosphate,monobasic, NaH2PO4H2O, 0.5g

Questions:

Pre-lab Questions-

1. As the concentration of potassium iodide increases, the solubility of iodine increases. The increase in the concentration of iodide ion causes the reaction to shift in the forward reaction. This allows more triiodide tions to be made and iodide to be consumed. Thus, more iodine solid are dissolved in the solution.

2. The concentration of NO at equilibrium increases when the reaction takes place at higher temperature due to the endothermic reaction. Since the reaction is endothermic, heat appears on the reactant side as seen in equation 5. When the reaction takes place at a higher temperature, it will shift the equilibrium in the forward reaction, absorbing some of the excess energy and making more products.

b.) The concentration of NO at equilibrium should not increase when the reaction takes place at high pressures. Since there is an equal amount of moles of gas on both the reactant and product side, the increase in pressure has no effect on the concentration of NO at equilibrium.

Analysis of Results-

1. Fe3+(aq) + SCN–(aq) ←→ FeSCN2+(aq)

Yellow Colorless Red-burgundy

2. Adding Fe(NO3)3 or KSCN produced the same color effect to the solution. It changed the color of the solution to a darker red/burgundy color. This shows that an increase in the amount of products. Since the concentration of the reactant increased by adding more reactants, the forward rate of reaction increases. Thus, more products are produced and the concentration of the products increases.

3. When KNO3 was added, no color change occurred. This shows that the ions of KNO3 were not involved in the equilibrium equation.

4. When NaH2PO4 was added, the color of the solution turned a lighter red/burgundy and the color was lighter around the solid. The H2PO4– ion decreased the concentration of the reactant and the amount of product decreased. Thus, the rate of the reverse reaction increased to form more