Displacement reactions :

Reactions of chlorine, bromine, and iodine with potassium chloride, potassium bromide and potassium iodide.

In these reactions we determine which of the halogens chlorine, bromine or iodine is the strongest.

Potassium iodide + chlorine gas

/ In this reaction when potassium iodide solution is put into chlorine gas:
a rapid reaction occurs.
black iodine solid is formed along with potassium chloride solution.
The chlorine has kicked the iodide out.

CHLORINE is stronger than IODINE

The equation for the reaction is:

potassium iodide / + / chlorine gas / / potassium chloride / + / iodine
2KI / + / Cl2 / 2KCl / + / I2

Potassium bromide + chlorine gas

/ In this reaction when potassium bromide solution is put into chlorine gas
a rapid reaction occurs
brown bromine liquid is formed along with potassium chloride solution.
The chlorine has kicked the bromide out.

CHLORINE is stronger than BROMINE

The equation for the reaction is:

potassium bromide / + / chlorine gas / / potassium chloride / + / bromine
2KBr / + / Cl2 / 2KCl / + / I2

Potassium chloride + chlorine gas

/ In this reaction when potassium chloride solution is put into chlorine gas –
No reaction occurs.

CHLORINE and CHLORIDE are of equal STRENGTH - hence no reaction

Potassium iodide + bromine liquid

/ In this reaction when potassium iodide solution is put into bromine liquid :
a rapid reaction occurs
black iodine solid is formed along with potassium bromide solution.
The bromine has kicked the iodide out.

BROMINE is stronger than IODINE

The equation for the reaction is:

potassium iodide / + / bromine vapour / / potassium bromide / + / iodine
2KI / + / Br2 / 2KBr / + / I2

From these findings the order of reactivity is (STRONGEST FIRST)

CHLORINE BROMINE IODINE