Silicon is the second most abundant element by mass in the Earth's crust.

1. (a)(i)Explain why the entropy change, ∆S, of reaction 1 is positive.[1]
2. (a)(ii)Reaction 1 is highly endothermic. Suggest the effect of an increase in temperature on the feasibility of this reaction. Explain your answer.[2]
3. (b)(i)Table 2.1 shows some standard entropy data. Table 2.1 compound standard entropy, S°/JK⁻¹mol⁻¹ Si(s) 19 HCl(g) 187 SiHCl3(g) 314 H2(g) 131 Use the data in Table 2.1 to calculate ∆S° for reaction 2.[2]
4. (b)(ii)Reaction 3 is the reverse of reaction 2 and is used to obtain pure silicon. reaction 3 SiHCl3(g) + H₂(g) → Si(s) + 3HCl(g) ∆H = +219.3 kJ mol⁻¹ Use this information and your answer to (b)(i) to calculate the temperature, in K, at which reaction 3 becomes feasible. Show your working. [If you were unable to answer (b)(i), you should use ∆S° = −150JK⁻¹mol⁻¹ for reaction 2. This is not the correct answer to (b)(i).][2]
5. (c)Silicon can also be produced by electrolysis of SiO2 dissolved in molten CaCl2. The relevant half-equation for the cathode is shown. SiO2 + 4e⁻ → Si + 2O²⁻ Calculate the time, in seconds, required to produce 1.00g of Si by this electrolysis, using a current of 6.00A. Assume no other substances are produced at the cathode.[2]

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