9.3 EFFECT OF HEAT (TEMPERATURE) ON A CHEMICAL EQUILIBRIUM SYSTEM

Activity:

Materials required: Test tube, dropper, heating system, hydrated copper(ll) sulphate.

Procedure:

1. Place 5 g of hydrated copper (ll) sulphate in a test tube. and heat slowly.
2. Observe the colour change from blue to white.
3. Allow the test tube and its contents to cool to room temperature.
4. Add a few drops of water to the test tube using a dropper.

NOTE:

Observe the colour change from white to blue again. When copper (II) sulphate is heated, the water in it is removed, forming anhydrous copper (II) sulphate, which is a white solid. This copper (II) sulphate changes back to the hydrated form on adding water.

Note: Copper sulphate is a harmful and toxic compound, so handle it with care. Wear safety glasses and gloves. Do this task in the presence of your teacher.

CuSO₄.5H₂O (blue solid) → CuSO₄ (white solid) + 5H₂O

Likewise
Hydrated cobalt(II) chloride is a pink solid. When heated, it loses water and becomes anhydrous cobalt(II) chloride, a blue solid. So the equilibrium shifts towards the right. But when water is added to it, it absorbs water and the equilibrium shifts to the left to form hydrated cobalt (II) chloride again.

CoCl₂.6H₂O (pink solid) → CoCl₂ (blue solid) + 6H₂O

KEY POINTS

• A reaction in which the products can react together to re-form the original reactants is called a reversible reaction.
• A reversible reaction is shown by the symbol →.
• Anhydrous copper(ll) sulphate is a white solid.
• Hydrated copper(ll) sulphate is a blue solid.
• Anhydrous cobalt (ll) chloride is a blue solid.
• Hydrated cobalt(ll) chloride is a pink solid.
• A state of a chemical reaction in which forward and reverse reactions take place at the same rate is called chemical equilibrium.

References for additional information

• Chemistry, Roger Norris, Lawrie Ryan, and David Acaster.
• Principles of chemical equilibrium, Kenneth Denbigh.