ENDOTHERMIC AND EXOTHERMIC REACTIONS
Experiment 1: A metal with an acid
Aim:
To determine how much energy is released when 1.0 mol of magnesium reacts with
hydrochloric acid
Method: Place 25 cm3 of 2.0 mol dm-3 hydrochloric acid in a polystyrene beaker. Record the
temperature. Accurately weigh out 0.05-0.10 g magnesium ribbon and record its mass.
Place the magnesium ribbon in the beaker and record the temperature every 10 seconds
until you see the maximum/minimum.
Analysis: 1.
2.
3.
4.
5.
Write a balanced equation for the reaction.
Calculate how much heat energy was released (ΔH = -m.c.ΔT) in your experiment.
Calculate the number of moles of magnesium you used.
Use your answers to 2 and 3 to calculate how much heat energy is released per mole.
Draw and fully label a reaction profile diagram for this reaction.
Experiment 2: The reaction of barium hydroxide with ammonium nitrate
Aim:
To observe the reaction of barium hydroxide (Ba(OH)2.8H20) with ammonium chloride to make
barium chloride, ammonia and water.
Method:
Place 9.6 g barium hydroxide in a boiling tube and record the temperature. Add 3.0 g
ammonium nitrate to the boiling tube. Lightly place a stopper on the tube and shake until liquid
starts to form. Remove the stopper and record the temperature every 30 seconds until you see
it hits a maximum/minimum. Gently test the smell of the test-tube. Place a piece of damp red
litmus paper over the mouth of the tube.
Analysis:
6.
7.
8.
9.
Write a balanced equation to describe the reaction.
Where do you think the liquid came from?
What is responsible for the potent smell and the colour change in the litmus paper?
Why does the observed change in temperature happen (saying it is
endothermic/exothermic is not enough).
10. Draw and fully label a reaction profile for this reaction.
Experiment 3: The thermal decomposition of a carbonate
Aim:
To observe the thermal decomposition of lithium carbonate to make lithium oxide, followed
by the reaction of lithium oxide with water
Method:
Place one spatula of lithium carbonate in a boiling tube. Heat strongly in a Bunsen burner
flame and record all observations. Allow lithium oxide to cool and tip oxide onto a watch-glass
and allow to cool. Place 25 cm3 water in a polystyrene beaker and record temperature. Add
cool lithium oxide and record maximum/minimum temperature observed.
Analysis:
11. Write balanced equations (including state symbols) for both parts of the experiment.
12. Draw and fully label a reaction profile for each stage of the reaction.
Experiment 4: A displacement reaction
Aim:
To observe the reaction of zinc with copper sulphate
Method:
Place 50 cm3 of 0.5 mol dm-3 copper sulphate solution in a polystyrene beaker. Record the
temperature. Add 3.0g of zinc. Record the temperature every 30 seconds until a
maximum/minimum has been reached.
Analysis:
13. Write a full balanced equation for the reaction.
14. Calculate how much heat energy was released
15. Calculate the number of moles of zinc and copper sulphate present and hence the limiting
reactant.
16. Use your answers to 13 and 14 to calculate the heat energy released per mole of reaction.
17. Why does the observed reaction take place? (Give you answer in terms of stability and
reactivity).
18. Draw and fully label a reaction profile for each stage of the reaction.