NYJC 2023 H2 Chemistry 9729 P2

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/02 Paper 2 Structured Questions 12 September 2023 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /11 2 /20 3 /20 4 /24 Total /75 This document consists of 21 printed pages.

2 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM Answer all the questions in the spaces provided. 1 Nitrosyl chloride, NOCl decomposes at temperatures above 100 oC to form nitrogen monoxide and chlorine as shown in the equation below. 2NOCl(g)  2NO(g) + Cl2(g) (a) (i) A sample of NOCl was allowed to decompose at 150 ºC and 125 atm. Assuming that NOCl behaves ideally, show that its initial concentration is 3.60 mol dm−3. [1] (ii) A student pointed out that the assumption in (a)(i) that NOCl behaves ideally is not valid. Suggest and explain two possible reasons why this may be so. [2]

3 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM [Turn Over (b) (i) In order to determine the rate equation for this reaction, an investigation was carried out at constant temperature for each experiment. The following results were obtained. initial rate / N m−2 s−1 16.2 47.2 78.8 124 172 ρNOCl / N m−2 0.30 0.50 0.66 0.82 0.95 (ρNOCl)2 / N2 m−4 0.09 0.25 0.44 0.67 0.90 Use these data to plot a suitable graph on the grid below to determine the order of reaction with respect to ρNOCl. [3] (ii) Hence, deduce the order of reaction with respect to ρNOCl. [1] (iii) Construct the rate equation for the decomposition of NOC l and state the units of the rate constant. [1]

4 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM (c) Explain, with the aid of a labelled Boltzmann distribution diagram, the effect on a rate constant of increasing temperature from T1 to T2. [2] (d) The reverse of the decomposition reaction can also occur such that NOC l is formed from NO and Cl2. Given that a possible mechanism for the reaction is as shown below, suggest the rate equation for the reaction. 22 fastStep 1: NO NO N O 2 2 2 slowStep 2: C N O 2NOC  ll [1] [Total: 11]

5 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM [Turn Over 2 The theoretical value of lattice energies can be estimated using a pure ionic model represented by the Kapustinskii equation as shown, where z+ and z are the charges on ions, r+ and r are the ionic radii in nm, v is the number of ions in the formula unit, and k is a constant with a value of 107.9 nm kJ mol─1.    rr zzvk Table 2.1 shows the theoretical lattice energies calculated from the Kapustinskii equation and experimental lattice energies obtained from the Born-Haber cycle for silver chloride, AgC l, and silver iodide, AgI. Table 2.1 compound experimental value / kJ mol─1 theoretical value / kJ mol─1 AgCl 916 729 AgI 889 618 (a) (i) Define the term lattice energy. [1] (ii) Use the Data Booklet to explain why the theoretical value of lattice energy for AgCl is more exothermic than AgI. [1] (iii) Suggest a reason for the difference in the theoretical and experimental values of lattice energy for AgCl. [1] (iv) Suggest a reason for the larger difference in the theoretical and experimental values of lattice energy for AgI as compared to AgCl. [1]

6 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM (b) Calcium and chlorine forms CaC l2 but not CaC l even though the enthalpy change of formation of CaC l is exothermic. CaC l does not exist as it will undergo disproportionation reaction readily to form CaCl2 and calcium. 2CaCl(s)  Ca(s) + CaCl2(s) (i) Use the Data Booklet and the Kapustinskii equation to calculate the theoretical value of lattice energy for CaCl and CaCl2. Assume the ionic radius of Ca+ to be 0.133 nm. [2] (ii) Using the answer in (b)(i) and data from Table 2.2, together with data from the Data Booklet , construct a Born -Haber cycle to calculate the enthalpy change of formation of CaCl. Table 2.2 ∆H / kJ mol─ standard enthalpy change of atomisation of Ca(s) +178 electron affinity of chlorine, Cl(g) + e─ → Cl─(g)  [4]

7 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM [Turn Over (iii) Use the data in Table 2.3 to calculate a value of y. Table 2.3 equation reaction ∆H / kJ mol-1 1 2CaCl(s)  Ca(s) + CaCl2(s) ∆Heqn1 = y 2 Ca(g)  Ca(s) ∆Heqn2 = 178 3 Ca2+(g) + 2Cl─(g)  CaCl2(s) ∆Heqn3 from (b)(i) 4 Ca+(g)+ Cl─(g)  CaCl(s) ∆Heqn4 from (b)(i) 5 Ca(g)  Ca+(g) + e─ ∆Heqn5 = +590 6 Ca+(g)  Ca2+(g) + e─ ∆Heqn6 = +1150 [3]

8 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM (c) Silver chloride, AgC l, and silver iodide, Ag I, are sparingly soluble in water. Table 2.4 shows the solubility and the solubility products of AgCl and AgI at 298 K. Table 2.4 salt solubility / mol dm─ solubility product / mol2 dm─ AgCl 1.4 × 10─ 2.0 × 10─ AgI 8.9 × 10─ 8.0 × 10─ (i) Explain, in terms of the interaction formed with water molecules, why the solubility of AgCl in water is higher than AgI. [2] (ii) When a precipitate is formed, ∆Go ppt, in J mol ─ , is given by the following expression. ∆Go ppt = 2.303 RT log Ksp Use the data in Table 2.4 to calculate ∆Go ppt, in kJ mol ─ , for the formation of the precipitate AgCl(s). [1] (iii) The standard enthalpy change of formation of the precipitate AgCl(s) i s 66.0 kJ mol−1. Use your answer in (c)(ii) to calculate ∆So ppt for the formation of the precipitate AgCl(s).

9 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM [Turn Over [1]

10 H2 Chemistry 9729/02 NYJC J2/2023 PRELIM (iv) Explain the significance of the sign in your answer in (c)(iii). [1] (v) Explain how the solubility of AgC l(s) will change when the te mperature is increased. [2] [Total: 20]