1. 5.1 Exothermic and endothermic reactions 18 October 2015 Exoskeletons Endoskeletons What do the words endo and exo mean before a word?

2. 5.1 Exothermic and endothermic reactions Energy is involved in chemical reactions. Energy changes in a chemical reaction can be measured. 18 October 2015 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!

3. Exothermic reactions Exothermic reactions give out heat to the surroundings e.g. burning, respiration How can you tell a reaction is exothermic? 25 o C 45 o C magnesium Hydrochloric acid Gets hot Heat energy given out

4. Cools Heat energy taken in as the mixture returns back to room temp. Starts 25°C Cools to 5°C Ammonium nitrate Water Endothermic reactions cause a decrease in temperature. Returns to 25°C Endothermic Reactions

5. Measuring energy changes 1.Measure 25 cm 3 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.

6. 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.

7. 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. 18 October 2015 Quiz next

8. Exothermic or endothermic? Hold up your card with ‘Exothermic’ or ‘Endothermic’ written on it to vote!

9. Thermal decomposition of marble? Endothermic

10. Combustion of methane? Exothermic

11. Photosynthesis? Endothermic

12. Neutralisation of an acid and an alkali? Exothermic

13. Rusting of iron? Exothermic

14. Thermal decomposition of copper carbonate? Endothermic

15. Respiration? Exothermic The End!

16. The reaction can be used for making cold packs to reduce the pain and damage caused by burns, sprained ankles or bruises. collect goggles, 100 ml beaker, thermometer dispense 30 ml citric acid solution into 100 ml beaker measure starting temperature (make sure it is stable) add 1 spatula of sodium bicarbonate and stir gently using the thermometer when the fizzing subsides, record the temperature repeat adding 1 spatula of sodium bicarbonate, stirring and recording Endothermic reaction