Introduction to Reversible Reactions

1. Topic: Equilibria

2. Discuss in your pairs and describe the above equation as
much as you can on your mini WBs
Starter
• In the forward reaction A and B are the reactants
and C and D are the products.
• In the reverse reaction C and D are the reactants
and A and B are the products.
• The forward reaction is exothermic which means
the reverse reaction is endothermic
• The same amount of energy given out in the
forward reaction is the same amount of energy
taken in in the reverse reaction.
Energy is given out

3. Practical
CuSO4.5H2O CuSO4 + 5H2O
hydrated copper sulfate (blue) anhydrous copper sulfate
(white)
Energy taken in
Predict the following:
What would you observe when the hydrated copper sulfate
is heated?
After heating the test tube is left to cool, what do you think
will happen when a few drops of water is added to the
white solid
How do you think the test tube will feel to touch when
water is added to the white solid?

4. Method
• Add a spatula of hydrated copper sulfate (CuSO4.5H2O) into
a boiling tube
• Using tongs and holding the test tube away from your body
heat on the Bunsen burner till all the solid turns white
• Leave the boiling tube to cool.
• Once the boiling tube has cooled down add a 2-3 drops of
water using a dropper.
• Carefully touch the boiling tube to determine if a
temperature change has occurred
See if your predictions are right!

5. Quick questions
In your notebooks:
1. A reversible reaction takes in 50 kilojoules (KJ) of
energy in the forward reaction. In this reaction A
gets broken down in B and C.
(a) Write an equation to show the reversible reaction
(b)What can you say about the energy transfer in
the reverse reaction?

6. 2. Blue cobalt chloride crystals turn pink when they
become damp. The formula for the 2 forms can be
written as CoCl2.2H2O and CoCl2.6H2O.
(a) How many moles of water will combine with 1
mole of CoCl2.2H2O to form CoCl2.6H2O
(b)Write a balanced equation for the reaction,
which is reversible.
(c) How can pick cobalt chloride crystals be changed
back to blue cobalt chloride crystals?
(d)What can this reaction be used to test for?

7. Learning objectives
• understand that some reactions are reversible and
are indicated by the symbol ⇌ in equations
• describe reversible reactions such as the
dehydration of hydrated copper(II) sulphate and
the effect of heat on ammonium chloride