Chem Energy of Rxn Ws2

Secondary 4 Express Pure Chemistry – Energy of Reactions Wksheet 2 Page 1 of 3 Name: ______________________( ) Class: _________ Date: __________ Section A: Multiple Choice Questions 1 Which of the following is an endothermic reaction? A the reaction of nitrogen with oxygen in a car engine B the oxidation of carbon to carbon dioxide C the combustion of ethanol in air D the reaction of magnesium with dilute sulphuric acid 2 The formation of hydrogen bromide from hydrogen and bromine is an exothermic reaction. H H + Br Br H Br + H Br What may be deduced from this information? A The number of bonds broken is less than the number of bonds formed. B Energy is given out in breaking H H and Br Br bonds. C The H Br bonds are weaker than the H H and Br Br bonds. D The total energy change in bond formation is greater than that in bond breaking. 3 The reaction scheme shows how paraffin wax (C40H82) is converted into carbon dioxide and water in four stages. Which stages are exothermic? A I and II B I, II and III C III and IV D I and IV 4 When solid potassium iodide is added to water, the temperature of the liquid decreases. What deduction can be made from this observation? A The change is endothermic. B New bonds are made in the change. C The change is exothermic. D The solid forms ions in water. Section B: Structured Questions C40H82(s) C40H82(l) C40H82(g) 40CO2(g) +41H2O(g) Stage I Stage II Stage III Stage IV 40CO2(g) +41H2O(l)

Secondary 4 Express Pure Chemistry – Energy of Reactions Wksheet 2 Page 2 of 3 1 Samples of two compounds were dissolved in water at 28oC. The temperature of each solution was measured immediately after the solid had dissolved. name of compound formula of compound temperature / oC water solution temperature change on dissolving solid potassium carbonate 28 35 ammonium chloride 28 16 (a) Complete the table. [4] (b) State the type of energy change which takes place when ammonium chloride dissolves in water. Give a reason for your answer. type of energy change: .....................................