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AQA Specimen Paper 2 Q2
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![Butadiene dimerises according to the equation 2C4H6 C8H12 The kinetics of the dimerisation are studied and the graph of the concentration of a sample of butadiene is plotted against time. The graph is shown in Figure 1. Figure 1 [Butadiene] / mol dm3 0.020 0.018 0.016 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0.000 . 1 0 2 1000 2000 3000 4000 5000 6000 7000 8000 9000 Time / s Draw a tangent to the curve when the concentration of butadiene is 0.0120 mol dm3. [1 mark] Barcode Typesetter code<br />
0 2 . 2 The initial rate of reaction in this experiment has the value 4.57106 mol dm3 s1. Use this value, together with a rate obtained from your tangent, to justify that the order of the reaction is 2 with respect to butadiene. [5 marks] Turn over for the next question Barcode Typesetter code Turn over <br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_QP_-_Paper_2_AQA_Chemistry_A-Level_2-0.jpg)
![Question 02.1 Gradient drawn on graph MARK SCHEMEA-level ChemistrySpecimen paper 2 Marking guidance Mark AO Comments AO3 1a Line must touch the curve at 0.012 but must not cross the curve. 4 of 20<br />
Stage 1: Rate of reaction when concentration = 0.0120 mol dm3 From the tangent Change in [butadiene] = 0.01600 and change in time = 78000 Gradient = (0.01600)/(78000) = 2.05106 Rate = 2.05106 (mol dm3 s1) Stage 2: Comparison of rates and concentrations Initial rate/rate at 0.0120 = (4.57106)/(2.05106) = 2.23 Inital concentration/concentration at point where tangent drawn = 0.018/0.012 = 1.5 Stage 3: Deduction of order If order is 2, rate should increase by factor of (1.5)2 = 2.25 this is approximately equal to 2.23 therefore order is 2nd with respect to butadiene AO3 1a AO3 1a AO3 1a AO3 1a AO3 1b 1 1 1 1 1 02.2 MARK SCHEMEA-level ChemistrySpecimen paper 2 Extended response Marking points in stage 2 can be in either order 5 of 20<br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_MS_-_Paper_2_AQA_Chemistry_A-Level_2-0.jpg)
