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Edexcel Jun 2009 Paper 1 Q24
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![24 Propanone, C3H6O, undergoes complete combustion to form carbon dioxide and water. C3H6O(l) + 4O2(g)3CO2(g) + 3H2O(l) (a) In an experiment to calculate the enthalpy change of combustion for propanone, 2.90 g of propanone was burned completely in oxygen. The heat energy from this combustion raised the temperature of 200 g of water from 20.2 C to 78.4 C. The specific heat capacity of water is 4.18 J g1C1. (i) Calculate the number of moles of propanone present in 2.90 g. [The molar mass of propanone is 58 g mol1.] (1) (ii) Use the expression energy transferred (J) = massspecific heat capacity temperature change to calculate the heat energy transferred to raise the temperature of 200 g of water from 20.2 C to 78.4 C. (2) (iii) Use your answers to (a)(i) and (ii) to calculate a value for the enthalpy change of combustion of propanone. Give your answer to three significant figures and include a sign and units. (3) *H34471A02328* 23 Turn over<br />
(b) In another experiment, the enthalpy change of combustion for butanone, C4H8O, was found to be 1300 kJ mol1. A Data Book value for the standard enthalpy change of combustion for butanone is 2440 kJ mol1. (i) Suggest a reason why the value obtained in the experiment is so different from the Data Book value. (1)(ii) This Data Book value (2440 kJ mol1) refers to the following equation. C4H8O(l) + 1O2(g)4CO2(g) + 4H2O(l) How would the value be different if it referred to the formation of water in the gaseous state? Justify your answer. (2) DifferenceJustification(c) Standard enthalpy changes of combustion can be used to calculate the standard enthalpy change of formation of a compound. (i) Define the term standard enthalpy change of formation, making clear the meaning of standard in this context. (3)24 *H34471A02428*<br />
(ii) Use the standard enthalpy changes of combustion, Hc , given in the table below to find the standard enthalpy change of formation for ethanoic acid, CH3COOH, in kJ mol1. Substance C(s, graphite) H2(g) CH3COOH(l) Hc / kJ mol1 394 286 870 2C(s, graphite) + 2H2(g) + O2(g)CH3COOH(l) (3) (Total for Question 24 = 15 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS *H34471A02528* 25<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJune_2009_QP_-_Unit_1_Edexcel_Chemistry_A-level_24-0.jpg)
![Reject Reject Reject Reject Mark Mark Mark Mark Question Number 23 (e)(ii) Question Number 24 (a)(i) Question Number 24 (a)(ii) Question Number 24 (a)(iii) Correct Answer 2 (aq)SrSO4(s) Sr2+(aq) + SO4 species (1) state symbols (1) 2nd mark is cq on first mark Sr2+(aq) + 2Cl(aq) + 2Na+(aq) + SO4 2Na+(aq) scores (1) SrCl2(aq) + Na2SO4(aq) (cid:198) SrSO4(s) + 2NaCl(aq) scores (1) 2(aq)SrSO4(s) + 2Cl(aq) + Correct Answer 2.90 = 0.05(00) (mol) 58 correct answer only (1) Correct Answer 200 x 4.18 x 58.2 = 48655 (J) OR 48.655 kJ (1) for correct T(1) IGNORE sf IGNORE signs at this stage Correct Answer48655 = 973 100 (J mol-1) 0.0500 = 973 kJ mol-1 (3 s.f.) / 973000 J mol-1 (3 s.f.) answer (1) sign and units (1) [Do not award sign and units mark if units given are just kJ or just J] three sig figs (1) CQ on (a)(i) & (ii)<br />
Mark Mark Mark Correct Answer Reject Heat loss/energy loss Accept Incomplete combustion OWTTE IGNORE experimental error/ departure from standard conditions Anything related to average values (0) Correct Answer Reject Just higher (0) Just H2O(g) is not waters standard state Difference: less exothermic / less negative IGNORE higher if written with less exothermic/less negative Accept just lower/ less (1) Justification: energy taken in to form gas/energy required to form gas/energy needed to form gas/takes heat in to form gas/heat required to form gas Or reverse argument (1) Mark these two points independently Correct Answer Reject Enthalpy / energy / heat (energy) change (when) one mole of a substance/one mole of a compound (1) is formed from its elements (in their most stable states) (1) 298K / 25C / a stated temperature AND 1 atm pressure/100 kPa energy required OR energy released one mole of product(s) is formed from its reactants room temperature/rtp Question Number 24 (b)(i) Question Number 24 (b)(ii) Question Number 24 (c)(i) IGNORE any references to concentration (1)<br />
Reject Mark Question Number 24 (c)(ii) Correct Answer Cycle or formula expression +2O2 +2O2 H1 H2 2CO2(g) + 2H2O(l) H = (2 x - 394) + (2 x - 286) - ( - 870) = 490 (kJ mol-1)f = H1 - H2correct expression or cycle (1)evidence for doubling bothc [C] and Hc [H2 ] H (1)answer (1) Correct answer with no working scores full marks<br />](https://learnah.org/wp-content/uploads/2018/08/June_2009_MS_-_Unit_1_Edexcel_Chemistry_A-level_24-0.jpg)
