5.1 Exothermic and endothermic reactions

April 20, 2023

Exoskeletons

Endoskeletons

What do the words endo and exo mean before a word?

5.1 Exothermic and endothermic reactions

• Energy is involved in chemical reactions.• Energy changes in a chemical reaction

can be measured.

April 20, 2023

The space shuttle main engines burn hydrogen and oxygen in an exothermic reaction at 3400°C. The three engines produce the equivalent of 37 million horsepower!

Exothermic reactions• Exothermic reactions give out heat to the

surroundings e.g. burning, respiration

How can you tell a reaction is exothermic?

25o C 45o Cmagnesium

Hydrochloricacid

Gets hot Heatenergygivenout

Cools

Heatenergytakenin as the mixture returns back to room temp.

Starts 25°C Cools to 5°C

Ammoniumnitrate

Water

Endothermic reactions cause a decrease in temperature.

Returns to 25°C

Endothermic Reactions

Measuring energy changes

1. Measure 25 cm3 of copper sulfate solution (HARMFUL) into the coffee cup.

2. Measure the temperature every 30 seconds for two minutes.

3. Add 1 g of zinc powder (FLAMMABLE) to the cup and quickly put on the lid and stir constantly.

4. Take the temperature every 20 seconds for three more minutes.

Method

Results

Draw a results table to show the temperature changes over 5 minutes.

Questions

1. Plot your results as a graph. What do you notice about the temperature during the reaction?

2. Is this reaction exothermic or endothermic? How do you know?

3. How could you improve this experiment? Think about where heat may be lost.

5.1 Exothermic and endothermic reactions

Most students should be able to:• State a definition for exothermic and endothermic

reactions.• List one example of an exothermic and

endothermic reaction.• Recognise an endothermic or exothermic reaction

when data is given.• Describe how a reaction can be monitored for its

energy changes.Some students should also be able to:• Explain the difference between exothermic and

endothermic reactions.

April 20, 2023

Quiz next

Exothermic or endothermic?

Hold up your card with ‘Exothermic’ or ‘Endothermic’

written on it to vote!

Thermal decomposition of marble?

Endothermic

Combustion of methane?

Exothermic

Photosynthesis?

Endothermic

Neutralisation of an acid and an alkali?

Exothermic

Rusting of iron?

Exothermic

Thermal decomposition of copper carbonate?

Endothermic

Respiration?

Exothermic

The End!