Take another minute to compare you ideas with a neighbour Learning objective: demonstrate the distinction between exothermic and endothermic reactions show how energy level diagrams can be used to summarize energy changes 28/04/2017 By yourself take a minute to come up with at least three examples of chemical changes involving an energy change. Take another minute to compare you ideas with a neighbour Share one example with the rest of the class.

Experiments 1 A test for water Put a spatula measure of white copper sulfate powder into a test tube. Add a few drops of water to the powder. Watch what happens and feel the bottom of the test tube. 2 The sherbet mixture In a dry test tube, mix one spatula measure of citric acid with one spatula measure of sodium hydrogencarbonate. Add 2 cm3 water to the mixture. 3 Competing Take about 5 cm3 copper sulfate solution in a test tube. Add a small measure of powdered zinc. Stir with a glass rod.

Results gives out energy (is exothermic) Substances mixed Observations Does the mixture get hotter or colder? Exothermic or endothermic? gives out energy (is exothermic) takes in energy (is endothermic)

Practical

Results gives out energy (is exothermic) Substances mixed Observations Does the mixture get hotter or colder? Exothermic or endothermic? ammonium nitrate + water anhydrous copper (II) sulfate + water sodium hydrogen carbonate, citric acid and water copper (II) sulfate + zinc White powders; fizzes and dissolves White powder; dissolves Blue soln & grey solid; soln loses colour & solid darker/red White powder turns blue; blue soln Colder Hotter Colder Hotter Endothermic Exothermic Endothermic Exothermic gives out energy (is exothermic) takes in energy (is endothermic)

Endothermic ammonium nitrate solid (NH4NO3 (s)) Diagram sheet Endothermic ammonium nitrate solid (NH4NO3 (s)) ammonium nitrate solution NH4+(aq) + NO3-(aq) water (aq) Energy taken in from the surroundings ammonium nitrate soln (NH4+(aq) + NO3-(aq)) Energy taken in from the surroundings ammonium nitrate solid (NH4NO3 (s)) + (aq)

Exothermic powdered zinc (Zn (s)) Energy released to the surroundings zinc sulfate soln (ZnSO4(aq)) copper sulfate soln (CuSO4(aq)) powdered copper (Cu (s)) Zn (s) + CuSO4 (aq) Energy released to the surroundings Cu (s) + ZnSO4 (aq)

Draw energy level diagrams for the other two reactions anhydrous copper (II) sulfate + water  hydrated copper (II) sulfate CuSO4 (s) + 5 H2O (l)  CuSO4.5H2O (s) sodium hydrogen carbonate + citric acid  sodium citrate + water + carbon dioxide 3 NaHCO3 (aq) + C3H5(COOH)3 (aq)  C3H5(COONa)3 (aq) + 3 H2O (l) + 3 CO2 (g)

Exothermic Endothermic CuSO4 (s) + 5 H2O (l) Energy released to the surroundings CuSO4.5H2O (s) C3H5(COONa)3 (aq) + 3 H2O (l) + 3 CO2 (g) Endothermic Energy taken in from the surroundings 3 NaHCO3 (aq) + C3H5(COOH)3 (aq)