TJC Prelim P2_Qn_&_Ans

1 9729/02/TJC Prelims/2018 [Turn over s CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 23 August 2018 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group, centre number, index number and name on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 18 printed pages For Examiner’s Use 1 / 21 2 / 13 3 / 9 4 / 8 5 / 14 6 / 10 Total / 75 PRELIMINARY EXAMINATIONS HIGHER 2

2 9729/02/TJC Prelims/2018 [Turn over SECTION A Answer all questions in the spaces provided. 1 (a) For many compounds, the enthalpy change of formation cannot be calculated directly. An indirect method based on enthalpy change of combustion can be used. The enthalpy change of combustion of butan-1-ol can be found by a calorimetry experiment in which the heat given off during combustion is used to heat a known mass of water and the temperature change recorded. temperature of water before heating = 25.0 °C temperature of water after heating = 66.1 °C mass of spirit burner and butan-1-ol before heating = 80.44 g mass of spirit burner and butan-1-ol after heating = 79.70 g (i) Explain the meaning of the term standard enthalpy change of combustion. • The standard enthalpy change of combustion of a substance , ΔHco, is the heat energy evolved when one mole of the substance is completely burnt in oxygen at 298 K and 1 bar. [1] (ii) The heat transfer from the spirit burner to water is known to be only 70% efficient. From the data provided above, determine the enthalpy change of combustion of butan-1-ol. mass of butan-1-ol reacted = 80.44 – 79.70 = 0.74 g No. of moles of butan-1-ol reacted = 0.74 / 74 = 0.0100 mol amount of heat taken in by water = mcΔT = 100 x 4.18 x (66.1 – 25.0) • = 17.2 kJ Heat provided by butan-1-ol = 100 x 17.2 / 70 = 24.6 kJ beaker 100 cm3 of water spirit burner butan-1-ol wick thermometer clamp