7.1. Chemical equilibria: reversible reactions, dynamic equilibrium
A subsection of Chemistry, 9701, through 7. Equilibria
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What is meant by the term standard electrode potential, SEP? Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the Fe3+ / Fe2+ electrode. The reaction between Fe3+ ions and I– ions is an equilibrium reaction. 2Fe3++ 2I–2Fe2++ I2Use the Data Booklet to calculate the for this reaction. Hence state, with a reason, whether there will be more products or more reactants at equilibrium. Write the expression for Kc for this reaction, and state its units. Kc = units An experiment was carried out using solutions of Fe3+and I–of equal concentrations. 100 cm3 of each solution were mixed together, and allowed to reach equilibrium. The concentrations at equilibrium of Fe3+and I2were as follows. [Fe3+] = 2.0 × 10–4 mol dm–3 = 1.0 × 10–2 mol dm–3 Use these data, together with the equation given in , to calculate the concentrations of Fe2+and I–at equilibrium. [Fe2+] = mol dm–3 [I–] = mol dm–3 Calculate the Kc for this reaction. Kc =
9701_s13_qp_41
THEORY
2013
Paper 4, Variant 1
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What is meant by the term standard electrode potential, SEP? Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the Fe3+ / Fe2+ electrode. The reaction between Fe3+ ions and I– ions is an equilibrium reaction. 2Fe3++ 2I–2Fe2++ I2Use the Data Booklet to calculate the for this reaction. Hence state, with a reason, whether there will be more products or more reactants at equilibrium. Write the expression for Kc for this reaction, and state its units. Kc = units An experiment was carried out using solutions of Fe3+and I–of equal concentrations. 100 cm3 of each solution were mixed together, and allowed to reach equilibrium. The concentrations at equilibrium of Fe3+and I2were as follows. [Fe3+] = 2.0 × 10–4 mol dm–3 = 1.0 × 10–2 mol dm–3 Use these data, together with the equation given in , to calculate the concentrations of Fe2+and I–at equilibrium. [Fe2+] = mol dm–3 [I–] = mol dm–3 Calculate the Kc for this reaction. Kc =
9701_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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