1. Exothermic and endothermic reactions

2. Objectives
Understand that in chemical reactions the total energy remains
the same
Definition of exothermic and endothermic reactions
Examples of exothermic and endothermic reactions
Everyday examples of exothermic and endothermic reactions

3. Chemical energy is the energy stored in the chemical bonds between the
atoms that make up the chemicals.
Thinking time: How many ways can you think of that this energy can be
used?

4. Producing heat by combustion
To produce light
Cells and batteries
The food we eat
Fuel cells for cars

5. During a chemical reaction the total amount of energy stays the same
What law is this?

6. Different chemicals store different amounts of energy.
If the products of a reaction store less than the reactants-excess
energy is transferred to the surroundings
If the products of a reaction store more than the reactants-energy
must have been taken from the surroundings
Definitions-to learn!

7. Chemical reactions where HEAT… Is transferred to the surroundings…
Exothermic
Endothermic
Chemical reactions where HEAT…
Is transferred to the surroundings…
Indicated by a RISE in temperature
Chemical reactions where HEAT…
Is transferred from the surroundings …
Indicated by a FALL in temperature

8. Let’s do this and see what happens!

9. Examples of exothermic reactions
combustion
neutralisation
Many oxidation reactions

12. Endothermic reactions
Thermal decomposition
CaC CaO CO2

13. Why is photosynthesis an
endothermic reaction?

15. Complete the following exercise:
Reaction
Starting Temp (OC)
End Temp (OC)
Temp Change (OC)
Exothermic or Endothermic? A 12 24 B 16 15 C
-12
-42 D -6 3 E -9 -2 F
106
144 G 37 39 H 21 9 I 43 -1