AQA A-level Chemistry Paper 2 (7405/2): Organic and Physical Chemistry Mark scheme 7405 Specimen paper

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A-level Chemistry Paper 2 (7405/2): Organic and Physical Chemistry Mark scheme 7405 Specimen paper Version 0.5MARK SCHEME – A-level Chemistry – Specimen paper 2 2 of 20 Question Marking gu... idance Mark AO Comments 01.1 Consider experiments 1 and 2: [B constant] [A] increases × 3: rate increases by 32 therefore 2nd order with respect to A Consider experiments 2 and 3: [A] increases × 2: rate should increase × 22 but only increases × 2 Therefore, halving [B] halves rate and so 1st order with respect to B Rate equation: rate = k[A]2[B] 1 1 1 AO3 1a AO3 1a AO3 1b 01.2 rate = k [C]2[D] therefore k = rate / [C]2[D] 1 AO2h k = (1.9 10 ) (3.5 10 ) 7.2 10 2 2 2 -4 - - × × × × = 57.0 1 AO2h Allow consequential marking on incorrect transcription mol–2 dm+6 s–1 1 AO2h Any order 01.3 rate = 57.0 × (3.6 × 10–2)2 × 5.4 × 10–2 = 3.99 × 10–3 (mol dm–3 s–1) OR Their k × (3.6 × 10–2)2 × 5.4 × 10–2 1 AO2hMARK SCHEME – A-level Chemistry – Specimen paper 2 3 of 20 01.4 Reaction occurs when molecules have E≥Ea Doubling T causes many more molecules to have this E Whereas doubling [E] only doubles the number with this E 1 1 1 AO1a AO1a AO1a 01.5 E a = RT(lnA – lnk)/1000 E a = 8.31 × 300 (23.97 – (–5.03))/1000 = 72.3 (kJ mol–1) 1 1 AO1b AO1b Mark is for rearrangement of equation and factor of 1000 used correctly to convert J into kJ [Show More]

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