7.1. Chemical equilibria: reversible reactions, dynamic equilibrium
A subsection of Chemistry, 9701, through 7. Equilibria
Listing 10 of 211 questions
1,2-diaminoethane, en, H2NCH2CH2NH2, is a bidentate ligand. What is meant by the terms bidentate and ligand? bidentate ligand There are three isomeric complex ions with the formula [Cr2Cl 2]+. Complete the three-dimensional diagrams of the isomers in the boxes. You may use N N to represent en. Cr Cr Cr Copper forms complexes with NH3 and en according to equlibria 1 and 2. equilibrium 1 Cu2++ 4NH3[Cu(NH3)4]2+equilibrium 2 Cu2++ 2en2+Write the expressions for the stability constants, Kstab1 and Kstab2, for equilibria 1 and 2. Include units in your answers. Kstab1 = units = Kstab2 = units = An equilibrium is set up when both en and NH3 ligands are added to a solution containing Cu2+as shown in equilibrium3. equilibrium 3 [Cu(NH3)4]2++ 2en2++ 4NH3Write an expression for the equilibrium constant, Keq3, in terms of Kstab1 and Kstab2. Keq3 = The numerical values for these stability constants are shown. Kstab1 = 1.2 × 1013 Kstab2 = 5.3 × 1019 Calculate the value of Keq3 stating its units. Keq3 = unit = ΔS o values for equilibria 1 and 2 differ greatly, as can be seen in the table. All values are at a temperature of 298 K. equilibrium ΔH o / kJ mol–1 ΔS o / J K–1 mol–1 ΔG o / kJ mol–1 –92 –60 –74 –100 +40 Explain why is so different from . Calculate at 298 K. = kJ mol–1 What conclusion can be made about the relative feasibility of equilibria 1 and 2? Explain your answer. Using data from the table, suggest a value of ΔH o for equilibrium 3. State the type of reaction that is occurring in equilibrium 2.
9701_s17_qp_42
THEORY
2017
Paper 4, Variant 2
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The elements sodium to chlorine, in the third period, all form oxides. Draw a diagram to show the shape of the molecule of each of the oxides, SO3 and Cl 2O. Name each shape. In SO3 each oxygen atom forms a double bond with the sulfur atom. SO3 Cl 2O  Explain why the melting point of MgO is higher than that of Na2O. Explain why the melting point of SiO2 is much higher than that of SO3. SO3 is produced by the reaction between SO2 and O2 in the Contact process. A dynamic equilibrium is established. 2SO2+ O22SO3∆H = –196 kJ mol–1 Explain why increasing the total pressure, at constant temperature, increases the rate of production of SO3 and increases the yield of SO3. rate yield  The graph shows how the concentrations of all three species in the system change with time for a typical reaction mixture. The gradients of all three lines decrease with time and then level off in this dynamic equilibrium. time concentration concentration of SO3 concentration of SO2 concentration of O2 Explain why the gradients of the SO2 and O2 lines decrease with time. Explain why all three lines become horizontal. Suggest a reason why the initial gradient of the SO2 line is steeper than that of the O2 line. 2.00moles of SO2and 2.00moles of O2are sealed in a container with a suitable catalyst, at constant temperature and pressure. The resulting equilibrium mixture contains 1.98moles of SO3. The total volume of the equilibrium mixture is 40.0 dm3. 2SO2+ O22SO3Write the expression for the equilibrium constant, Kc, for the reaction between SO2and O2to produce SO3. Kc =  Calculate the amount, in moles, of SO2and O2in the equilibrium mixture.  SO2= mol  O2= mol  Use your answers to and to calculate the value of Kc for this equilibrium mixture. Give the units of Kc.  Kc =  units =  
9701_s18_qp_23
THEORY
2018
Paper 2, Variant 3
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Silver carbonate, Ag2CO3, is sparingly soluble in water. The numerical value of the solubility product, Ksp, for silver carbonate is 6.3×10–12 at 25 °C. Write an expression for the solubility product, Ksp, of Ag2CO3, and state its units. Ksp =  units =  Calculate the equilibrium concentration of Ag+ in a saturated solution of Ag2CO3 at 25 °C.  [Ag+] = mol dm–3 Solid Ag2CO3 is stirred at 25 °C with 0.050 mol dm–3 AgNO3 until no more Ag2CO3 dissolves. Calculate the concentration of carbonate ions, [CO3 2–], in this solution.  [CO3 2–] = mol dm–3 An electrochemical cell is set up to measure the electrode potential, E, for the Ag+ / Ag half‑cell using the saturated Ag2CO3with a standard hydrogen electrode. Use the Data Booklet, your answer to , and the Nernst equation to calculate the electrode potential, E, for this Ag+ / Ag half-cell.  E for Ag+ / Ag half-cell = V Silverchloride, AgCl, is sparingly soluble in water. The equation for the enthalpy change of solution is shown. AgCl → Ag++ Cl –= +65.5 kJ mol–1 Standard entropies are shown in the table. species AgCl Ag+Cl –S o / J K–1 mol–1 +96.2 +72.7 +56.5 Calculate the standard entropy change of solution, ∆S o.  ∆S o = J K–1 mol–1 Explain, with the aid of a calculation, why AgCl is insoluble in water at 25 °C. You should use data from this question and your answer to . 
9701_s20_qp_41
THEORY
2020
Paper 4, Variant 1
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Silver carbonate, Ag2CO3, is sparingly soluble in water. The numerical value of the solubility product, Ksp, for silver carbonate is 6.3×10–12 at 25 °C. Write an expression for the solubility product, Ksp, of Ag2CO3, and state its units. Ksp =  units =  Calculate the equilibrium concentration of Ag+ in a saturated solution of Ag2CO3 at 25 °C.  [Ag+] = mol dm–3 Solid Ag2CO3 is stirred at 25 °C with 0.050 mol dm–3 AgNO3 until no more Ag2CO3 dissolves. Calculate the concentration of carbonate ions, [CO3 2–], in this solution.  [CO3 2–] = mol dm–3 An electrochemical cell is set up to measure the electrode potential, E, for the Ag+ / Ag half‑cell using the saturated Ag2CO3with a standard hydrogen electrode. Use the Data Booklet, your answer to , and the Nernst equation to calculate the electrode potential, E, for this Ag+ / Ag half-cell.  E for Ag+ / Ag half-cell = V Silverchloride, AgCl, is sparingly soluble in water. The equation for the enthalpy change of solution is shown. AgCl → Ag++ Cl –= +65.5 kJ mol–1 Standard entropies are shown in the table. species AgCl Ag+Cl –S o / J K–1 mol–1 +96.2 +72.7 +56.5 Calculate the standard entropy change of solution, ∆S o.  ∆S o = J K–1 mol–1 Explain, with the aid of a calculation, why AgCl is insoluble in water at 25 °C. You should use data from this question and your answer to . 
9701_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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