OCR A Jan 2012 Paper 2 Q4

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4 Hydrogen and chlorine are reacted together to form hydrogen chloride. H2(g) + Cl2(g) 2HCl(g) H = 184 kJ mol1 10 (a) Calculate the bond enthalpy for the HCl bond using the information in the table below. bond HH ClCl bond enthalpy / kJ mol1 +436 +243 bond enthalpy =kJ mol1 [2] (b) The reaction is repeated at a higher pressure. Describe and explain what happens to the rate of the reaction between H2(g) and Cl2(g).[2]OCR 2012<br />
 (c) The reaction is repeated again. This time the temperature is decreased. 11 Describe and explain, by drawing appropriately labelled Boltzmann distributions, what happens to the rate of reaction between H2(g) and Cl2(g).[5] (d) The mechanism of the reaction between H2(g) and Cl2(g) involves initiation, propagation and termination. (i) The initiation step is the homolytic fission of the covalent bond in a chlorine molecule. Write an equation to show this homolytic fission.[1] (ii) Complete the following equations which show the propagation steps. Cl + H2 H + Cl2++(iii) Suggest equations for two termination steps. [2][2]OCR 2012 [Total: 14] Turn over<br />

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