1. Unusual Reactions L.O: To understand what happens in some unusual chemical reactions

2. Mini white boards http://www.bbc.co.uk/apps/ifl/schools/g csebitesize/science/quizengine?quiz=ad d_aqa_quantitative_chemistryftest&te mplateStyle=science

3. You will be shown some reactions. You need to explain what you see and what you think is happening on your worksheet

4. Heating ammonium chloride Ammonium salts are made by reacting ammonia with an acid but some of these salts will decompose back into reactants when heated. Heat Heat makes the solid disappear as it changes into gases. Solid reappears as it changes back again in the cool part of the tube. ammonium chloride ammonia hydrogen chloride NH 4 Cl(s)NH 3 (g) + HCl(g) Which direction is giving out heat? And which is taking it in?

5. Now look at the other reactions on your sheet

6. ALL the reactions you have seen are reversible

7. A reversible reaction is where products can, under appropriate conditions, turn back into reactants. If the reaction releases energy in one direction (exothermic), it will take in same amount of energy in the other (endothermic). A B A B these combine these decompose Reversible Reactions

8. Mg + 2HCl  MgCl 2 + H 2 Irreversible reactions Most Chemical reactions are considered irreversible in that products are not readily changed back into reactants. When wood burns it is pretty difficult to un-burn it back into wood again! When magnesium reacts with acid it is not easy to unreact it and get back the magnesium. Wood reacting with oxygen

9. Simple reversible reactions Heating copper sulphate Explain what hydrated means Explain what anhydrous means Explain how copper sulphate can be used to test for water. hydrated copper sulphate Heat anhydrous copper sulphate steam CuSO 4.5H20 ⇌ CuSO 4 + 5H 2 O

10. Blue Cobalt crystals turn pink when they become damp. The formula for the two forms can be written as CoCl 2.2H 2 O and CoCl 2.6H 2 O 1.How many moles of water will combine with 1 mole of CoCl 2.2H 2 O 2.Write a reversible balanced equation 3.You have some pink cobalt chloride crystals. Suggest how you could turn them into pink cobalt crystals

11. The rate at which reactants change into products and products change into reactants will eventually become the same. So… the overall amount of reactants and products does not change. A B A B these combine these decompose Equilibrium

12. If we start with only reactants how will the rates change over time of reactants forming products, and products forming reactants? A B Lots of reactants forming products A B A B Rate of reactants to products is high Reversible rate is low A B A B Rate of reactants to products slows down Reversible rate increases A B A B Rate of reactants to products eventually equals the rate of the reversible reaction

13. A closed system In a closed system no reactants or products can get in or out Eventually a balance between the amounts of reactants and products is reached. (not necessarily the same amounts of each). Temperature and Concentration (Pressure) can change the amount of products and reactants.

14. 1.What is a reversible reaction? 2.If heat is lost in the forward reaction will the reverse be endothermic or exothermic? 3.What happens to the rate of a forward reaction over time if you start with reactants only. 4.What will happen to the rate of reaction in both directions when equilibrium is reached? 5.What two things could change the amount of reactants and products in a reversible reaction? 6.What is a closed system?

15. Why do you think reversible reactions are a problem to industries?