1. Thermal Decomposition
Connect
11 November, 2018
Thermal Decomposition
Key Words
Reactants
Products
Thermal
decompostion
LO: to recognise thermal decomposition reactions
Starter:
Name one exothermic reaction (1 mark)
Describe how you could detect an exothermic reaction (2 marks)
Extension: What are the energy transformations that could occur in an exothermic reaction? (3 marks) 1

2. Plenary questions (Just read it!)
After a fire, many brick built and concrete buildings become unsafe although they may look relatively undamaged.
Use your understanding of thermal decomposition to explain why

3. What are carbonates
A group of compounds with a CO32- group, e.g. CaCO3
What do you know about these compounds?
Some form rocks e.g. calcium carbonate is chalk
They react with acid
They produce carbon dioxide
+ they break down when heated

4. What is thermal decomposition?
Breaking down
Heat
A reaction in which a substance is broken down into at least two other substances by heat
DEMO COPPER CARBONATE
Reminder: gas tests here!

5. Energy changes during thermal decomposition (practical)
Heat 2 spatulas of Calcium carbonate powder in a boiling tube for about 3 minutes.
A gas is given, off how could you test for it?
Place the boiling tube in a rack to cool
Measure 20ml of water into a measuring cylinder
Measure the temperature of the water.
Poor the water into the boiling tube and re-test the temperature.

6. Energy change questions
When you heated the CaCO3,were you putting energy in or removing it?
Is thermal decomposition exo or endothermic?
What happened when you added water?
Extension: Explain why?

7. Calcium carbonate is used to make concrete and cement
Calcium carbonate is heated (with clay) to make cement powder.
So calcium carbonate decomposes to form calcium oxide and carbon dioxide.
To make concrete water and aggregate are added, then it is left to dry. Two reactions occur and the calcium carbonate is reformed.
Calcium oxide is soft and crumbly, calcium carbonate is much harder.
Think about the plenary question, pair and share.

8. Plenary questions
After a fire, many brick built and concrete buildings become unsafe although they may look relatively undamaged.
Use your understanding of thermal decomposition to explain why