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!