Everything Science Grade 12

CHAPTER 3. REACTION RATES 3.8

• If the concentration ofa reactant (on the left) is increased, then someof it must
  change to the products (on the right) for equilibrium to be maintained. The equi-
  librium position will shift to the right.


• If the concentration ofa reactant (on the left) isdecreased, then some ofthe prod-
  ucts (on the right) must change back to reactantsfor equilibrium to be maintained.
  The equilibrium positionwill shift to the left.


• A catalyst does not affect the equilibrium position of a reaction. It only influences
  the rate of the reaction, in other words, how quickly equilibrium is reached.

Activity: Le Chatelier’s Principle

Aim:

To determine the effectof a change in concentration and temperatureon

chemical equilibrium

Apparatus:

0.2 M CoCl 2 solution, concentrated HCl, water, test tube, bunsen burner

Method:

1. Put 4-5 drops of 0.2MCoCl 2 solution into a test tube.


2. Add 20-25 drops of concentrated HCl.


3. Add 10-12 drops of water.


4. Heat the solution for1-2 minutes.


5. Cool the solution for1 minute under a tap.


6. Observe and recordthe colour changes thattake place during the reac-
   tion.

The equation for the reaction that takes place is:

e.g. CoCl^24 −+ 6H 2 O

� �� �

blue

� Co(H 2 O)2+ 6 + 4Cl−

� �� �

pink

Results:

Complete your observations in the table below,showing the colour changes

that take place, and also indicating whether the concentration of eachof the

ions in solution increases or decreases.

Initial

colour

Final

colour

[Co2+] [Cl−] [CoCl^24 −]

Add Cl−

Add H 2 O

Increase

temp.

Decrease

temp.