Edexcel Jun 2017 Paper 4 Q16

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16 Hydrogen iodide partially decomposes into hydrogen and iodine. 2HI(g) (cid:85)(cid:1)H2(g) + I2(g) (a) A graph of the initial rate of reaction against the square of the initial concentration of hydrogen iodide is shown. Initial rate / mol dm3 s1 0.120.100.080.060.040.020.000 10 20 30 [HI]2 / mol2 dm6 40 50 (i) Deduce the order of reaction with respect to hydrogen iodide. Explain your reasoning. (2)(ii) Write the rate equation for the reaction. (1) 14 *P48082A01428* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (iii) In one of the experiments, the initial concentration of hydrogen iodide was 1.00 mol dm3 and the initial rate of reaction was 0.00620 mol dm3 s1. Use the data to calculate the number of molecules decomposing in the first minute in 1.00 dm3 of hydrogen iodide. Assume that the rate of reaction remains constant for the first minute. [Avogadro constant = 6.021023 mol1] (2) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48082A01528* 15 Turn over<br /> *(b) The activation energy for the forward reaction is 184 kJ mol1. 2HI(g) (cid:85)(cid:1)H2(g) + I2(g) At 700 K, the rate constant is 2.32103 dm3 mol1 s1. Calculate the rate constant at 800 K and give your answer to three significant figures. You should not attempt to use any graphical method to answer this question. The Arrhenius equation is [Gas constant, R = 8.31 J mol1 K1 and A is a constant] In k =E aR 1 T + A D O N O T W R I T E I N T H I S A R E A (5) D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A 16 *P48082A01628*<br /> (c) (i) Write the expression for the equilibrium constant, Kc , for the reaction. 2HI(g) (cid:85)(cid:1)H2(g) + I2(g) (ii) Explain why Kc for this reaction has no units. (1) (1) A E R A S I H T N I E T I R W T O N O DA E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48082A01728* 17 Turn over<br /> (iii) In an experiment to determine Kc , 0.192 g of hydrogen iodide, in a 1 dm3 vessel, was heated at 700 K until equilibrium was established. 0.00019 mol of iodine was present in the equilibrium mixture. Calculate the value of Kc at 700 K. (4) 18 *P48082A01828* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D *(iv) The enthalpy change for the forward reaction is +9.5 kJ mol1. State and explain the effect of an increase in temperature on the entropy change of surroundings, (cid:507)Ssurroundings , and hence on the value of Kc . (3)(Total for Question 16 = 19 marks) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48082A01928* 19 Turn over<br />

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