Process of the Shift in Equilibrium Experiment

Introduction

The shift in the state of equilibrium is noticed when, the system is disturbed. However, the experiment for the Shift in Equilibrium is conducted in the laboratory under controlled conditions. Le Chatelier's Principle states the concepts of shifting of equilibrium, is associated with equilibrium constant. The shift of equilibrium in the reaction is quite effective on the state of equilibrium. The shifting of reaction direction can be predicted accordingly.

Le Chatelier's principle

In a chemical reaction, the state of chemical equilibrium can be changed by making a change in the reaction conditions. The shift in the state of equilibrium is known as stress . Therefore, if stress is exerted on the state of equilibrium for a given system, the reaction will no longer at equilibrium.

Figure 1 − Graphical presentation of Le Châtelier's Principle

According to Le Chatelier's principle, addition or removal of number of moles of products or reactants, pressure, temperature, and any other changes in equilibrium reaction results in a remarkable shift to either forward or backward simultaneously to release the stress.

Equilibrium Constant

Equilibrium Constant is a necessary aspect to describe the equilibrium state of any reaction. The ratio of concentrations of product molecules to the reactant molecules is known as Equilibrium Constant. However, at particular temperature, the rate of equilibrium remains constant.

Aims and purpose

The aim of the below mentioned experiment is to understand the shifting of the equilibrium to exhibit the relation between reaction equilibrium and equilibrium constant. However, the reaction of Ferric ions and Thiocyanate ions is considered for the experiment, where, the concentration of ions is increased or decreased to observe the effect of stress on equilibrium state of reaction.

Materials required

Certain specific materials are required for this lab experiment that is stated below −

One spot plate made up with ceramics, followed by two stir rods of glass, a hot plate, 250mL of waste collection beaker is taken for the experiment. The MicroLab spectrophotometer and four MicroLab spectrophotometer vials are required.

Figure 2 − “Materials required”

The solution of 0.100g Ferric Chloride is added to 0.100g Potassium thiocyanate followed by further addition of deionized water.

Procedures

Several steps are maintained to achieve proper and accurate readings in this experiment with precautionary measurements. If the measurements are not done properly, then, the experiment will be invalid. Solution of 10 mL of 0.1 M $\mathrm{FeCl_{3}}$ is taken into measuring cylinder and poured into a clean beaker together with 10 ml of 0.1 M KSCN . A deep red colour is appeared due to formation of product complex molecule, $\mathrm{[Fe(SCN)(H_{2}O)_{5}]^{2+}\:\:(aq)}$ . The product molecule is diluted with 50 ml distilled water. Now the solution is poured into four beakers and stress is created.

Precautionary measures

Certain precautionary steps are required to carry out the experiment are mentioned below −

• The test tubes are used should be with exact diameters.

• For this lab experiment, dilute solutions of thiocyanate is required to carry out the experiment.

The comparison is done on the basis of intensity of colour observed during experiment. The colour appears after completion of reaction is considered as reference colour for the experiment.

Observations

The observation table is listed down as follows −

Test tubes	Substances added at equilibrium	Colour change	Effect on the concentration of $\mathrm{[Fe(SCN)(H_{2}O)_{5}]^{2+}}$	Shift noticed at the equilibrium
A	5 mL of water	Reference colour	N/A	N/A
B	5 mL of 0.1 M $\mathrm{FeCl_{3}}$ solution	Colour tends to get deeper	Increases	Shift towards the right
C	5 mL of 0.1 M KSCN solution	Colour tends to get deeper	Increases	Shift towards the right
D	5 mL of 0.1 M KCl solution	Colour becomes lighter	Increases	Shift towards the left

Table 1 − Change in state of equilibrium in presence of various conditions

Conclusion

In this tutorial, an intensive focus has been given to the laboratory experiment explained the possible changes in the state of equilibrium for a given reaction. However, Le Chatelier's Principle states that a shift in equilibrium takes place if stress is introduced. The experimental analysis is explained with the help of this principle.

FAQs

1. What is the reason behind the equilibrium experiment being carried out only with dilute solutions?

The reason that lies behind the equilibrium experiment being carried out only with dilute solutions is to handle and understand the colour change during generation of various stresses in the reaction. On an addition, concentrated solution may cause serious damage in laboratory due to elevation of heat during application of stress on it.

2. What is the reason behind the use of the same sized boiling tubes in the equilibrium experiment?

Boiling tubes are cylindrical vessels that are small in size is used in strongly heating substances in the flame from the Bunsen burner within lab conditions. The reason behind the use of the same sized boiling tubes within the experiment of equilibrium experiment is to get accurate measurements of the solution that are added for referential purposes.

3. How equilibrium constant does differ from rate constant?

The equilibrium constant remains independent in the initial concentration of reactants, whereas, the rate constant depends on the aspects of temperature.