1. What's Hot? Year 10 Science 2012 Section 1: Energy in Chemical reactions

2. Energy and Chemical Reactions Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions. There are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions.

3. Demonstration of exothermic and endothermic reactions Record your observations stating whether the reactions are exothermic or endothermic

4. Exothermic Reactions Exothermic reactions may occur spontaneously. Exothermic reactions produce heat or may even be explosive. An exothermic reaction is one which transfers heat energy to the surroundings

5. Some Exothermic Reactions

6. Magnesium + Hydrochloric acid Gets hot 25 o C 45 o C magnesium Hydrochloric acid Heat energy given out Exothermic Reactions

7. Examples of Exothermic reactions Skiers and mountain climbers often use hand warmers inside their gloves. These small heat packs rely on exothermic processes. Combustion is an example of an exothermic reaction

8. Bunsen burners burn methane: Cigarette lighters use butane to produce a flame: butane + oxygen carbon dioxide + water Alcohols are also flammable, for example: ethanol + oxygen carbon dioxide + water Chemistry is full of patterns What pattern do you see here? Combustion

9. Examples of exothermic processes Change of state When steam condenses into water, the water molecules lose energy and this energy is transferred to the surroundings. Similarly, when water freezes, the water molecules lose even more energy to the surroundings.

10. Exothermic Examples Chemical Reactions o A candle flame o Rusting iron o Burning sugar o Glow sticks o Fire crackers Physical processes o Some hand warmers o Some dissolving o Condensing o Freezing What do you think is the difference between a reaction and process?

11. Experiment

12. Complete page 69 Questions 1-8

13. Endothermic Reactions Endothermic reactions cannot occur spontaneously. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. An endothermic reaction is one which takes heat energy from the surroundings

14. Endothermic Reaction

15. Cools Heat energy Is used up during the reaction so the contents in tube feel cold Starts 25°C Cools to 5°C Ammonium nitrate Water Endothermic reactions cause a decrease in temperature. Endothermic Reactions

16. Example of Endothermic Reactions When you squeeze the plastic bag the water reacts with the ammonium nitrate crystals, and the reaction dissolves the ionic bonds in the ammonium nitrate.

17. Another example of Endothermic reactions An important endothermic reaction is photosynthesis. Plants need energy from sunlight to make glucose and oxygen from carbon dioxide and water.

18. Endothermic Processes Changes of state For ice to melt, the water molecules must gain energy. For water to boil and turn into steam, the water molecules must gain even more energy. These are both endothermic processes. Energy is needed to make these changes happen.

19. Endothermic Examples Chemical Reactions o Baking bread o Cooking an egg Physical Processes o Sometimes dissolving o Cold packs o Melting and boiling

21. Complete Page 71 questions 1- 5