10   4 This question is about the white solid barium carbonate. (a) Barium carbonate decomposes under suitable conditions to form barium oxide and carbon dioxide. BaCO3(s) → BaO(s) + CO2(g) ΔrH d = +169.3 kJ mol–1 Standard molar entropy data related to this reaction are shown. Substance Standard molar entropy, S d / J K–1 mol–1 BaCO3(s) 112.1 BaO(s) 70.4 CO2(g) 213.6 (i) Show that barium carbonate is thermally stable at 298 K, using the data in the equation and in the table. (5) Turn over 11   (ii) Calculate the lowest temperature, in °C, at which it is thermodynamically feasible for barium carbonate to decompose. Give your answer to three significant figures. (3) (b) Explain whether magnesium carbonate is more or less thermally stable than barium carbonate. 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(c) A white solid was thought to be barium carbonate. A student suggested that the presence of the carbonate ion could be tested for by adding a small amount of sulfuric acid. Explain whether or not this suggestion is valid. 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(Total for Question 4 = 13 marks) 12   5 * Explain the difference in the reactivity of bromine with benzene and with phenol. Include the type of reaction, the products that form, and any conditions required. Mechanisms for the reactions are not required. 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(Total for Question 5 = 6 marks)