Chemistry Lab Report - Chemical Equilibrium

1.     Title                      : Chemical equilibrium

2.     Objectives            : To know the effect of concentration changes toward chemical equilibrium

3.     Theory

Chemical equilibrium has been reached in a reaction when the rate of the forward reaction is equal to the rate of the reverse reaction. When a chemical reaction has reached equilibrium, collisions are still occurring: the reaction is now happening in each direction at the same rate. This means that reactants are being formed at the same rate as products are being formed, and this is indicated by double arrows, . At equilibrium, the reaction can lie far to the right, meaning that there are more products in existence at equilibrium, or far to the left, meaning that at equilibrium there are more reactants. The concentration of the reactants and products in a reaction at equilibrium can be expressed by an equilibrium constant, symbolized K or Keq.

If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change. A new equilibrium is established. This principle has a variety of names; in chemistry it is known as Le Chatelier's principle.

Because products and reactants in a chemical equation do not always have the same number of moles, as demonstrated in , disturbances in the concentration of atoms can affect the equilibrium. Changing the concentration of an ingredient will shift the equilibrium toward the side that reduces the concentration change. The chemical system will attempt to partially counteract the change imposed on the original state of equilibrium. In turn, the rate of reaction, extent, and yield of products will be altered in correspondence with the impact on the system.

In the course of a reaction, the total number of molecules can change. For instance, multiple molecules of the reactants (A and B) must be used to form a single molecule of product (C).

This can be illustrated by the equilibrium of carbon monoxide and hydrogen gas reacting to form methanol.

CO+2H2⇌CH3OH

Suppose we were to increase the concentration of CO in the system. Using Le Chatelier's principle, we can predict that the amount of methanol will increase, decreasing the total change in CO. If we add a species to the overall reaction, the reaction will favor the side opposing the addition of the species. Likewise, the subtraction of a species would cause the reaction to fill the 'gap' and favor the side where the species was reduced. This observation is supported by the collision theory. As the concentration of CO is increased, the frequency of successful collisions of that reactant would increase also, allowing for an increased forward reaction—increased generation of product. Even if a desired product is not thermodynamically favored, the end-product can be obtained if it is continuously removed from the solution.

4.     Tools and Materials

a.     Beaker glass

b.     Test tubes @5

c.     Measuring cylinder

d.     Aquades

e.     FeCl₃

f.      NaOH

g.     KSCN

h.     Stirring rod

i.      Pipette

5.     Procedure

a.     Take 25 ml of aquades into the beaker glass, measure 25 ml using beaker glass

b.     Put 2 drops of each FeCl₃ and KSCN into the beaker glass

c.     Stir it

d.     Put it into the five test tubes

e.     Tube 1, don’t put anything

f.      Tube 2, put 2 drops of KSCN using dropping pipette

g.     Tube 3, put 2 drops of FeCl₃ using dropping pipette

h.     Tube 4, put 2 drops of NaOH using dropping pipette

i.      Tube 5, add some aquades @5 ml using measuring cylinder

j.      Compare the color of the test tube to the tube 1

6.     Data

Attached

7.     Analysis

The test tube 2 shows the darker color compared to the tube 1, yet it is the darkest color among the 5 test tubes. While the tube 3, it shows the darker color, but it is not as dark as the tube 2. Yet, test tube 4 shows the lighter color compared to the test tube 1, and it shows the lightest color among five of them, and the last, test tube 5, it shows the lighter color compared to test tube 1, but not as light as tube 4.

Based on the data, Fe³⁺_(aq) + SCN^-_(aq)  [FeSCN]²⁺_(aq). If the concentration of SCN^- is increased, it will make the color of the solution become darker, because the equilibrium shift to the right, to the side of  [FeSCN]²⁺, while if the concentration of Fe³⁺ is increased, the color of the solution become darker, because the equilibrium shift to the right to [FeSCN]²⁺, and if the concentration of Fe³⁺ is decreased by adding NaOH, it will make the color become lighter, because the equilibrium shift to the left to Fe³⁺ + SCN^-.

If you add the water to the test tube, it will give you some effect which means you have dilution, which will make the equilibrium shift to the side with the greater number of mole. So, based on the experiment above, Fe³⁺_(aq) + SCN^-_(aq)  [FeSCN]²⁺_(aq), the left side has greater number of mole, the left has two moles, while the right side has one mole. Therefore, according to the theory, it will shift to the left side which will make the color become lighter.

There are some color changes due to the concentration changes. If you increase / add the concentration of reactant, e.g. FeCl₃ or KSCN, it will shift to the right, which will make the color darker. If you decrease the concentration of the reactant, e.g. adding NaOH so the Fe³⁺ will react with NaOH, will make the equilibrium shift to the left, which will make the color lighter. There are some ways to optimize the product in this experiment by increasing the concentration of the reactant, pressure, and decreasing the volume.

There are some factors affecting the chemical equilibrium, concentration, if you increase the concentration of reactant, it will make the equilibrium shift to the right, while if you decrease the concentration of the reactant, it will make the equilibrium shift to the left. Dilution, if you add some water, it will shift the equilibrium to the side with the greater total number of mole. While, temperature, if the reaction is endothermic, if you increase the temperature, the equilibrium will shift to the right, as also the vice versa. If the reaction is exothermic, if you increase the temperature, it will shift to the left, while if you decrease the temperature, it will shift to the right. Pressure, if you increase the pressure, it will shift to the side with fewer number of moles, and the volume, if you increase the volume of the solution, it will shift to the side with the greater number of mole.

8.     Conclusion

Hence, there are some factors affecting the chemical equilibrium, such as concentration, dilution, temperature, pressure, and volume. In this experiment, increasing the concentration of SCN^- will make the color darker and the equilibrium shift to the right, while if decreasing the concentration of Fe³⁺, it will make the color lighter, because it will shift to the left.

Edbert Prathama / 11 Philip / 2