MI Prelim H1 Chem P2 Ans for exchange

Class Adm No Candidate Name: This document consists of 22 printed pages and 2 blank pages. 2025 Preliminary Examination Pre-University 2 H1 CHEMISTRY 8873/02 Paper 2 Structured Questions 27 August 2025 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so. Write your name, class and admission number in the spaces at the top of this page. 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. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. Question Section A Section B Total 1 2 3 4 5 / 6 Marks 19 11 22 8 20 80 H Class Adm. No.

2 Section A Answer all the questions in this section in the spaces provided. 1 (a) Graphene is a nanomaterial. (i) Draw a diagram to represent part of a graphene layer which contains at least five complete rings of carbon atoms. [1] (ii) Graphene has high tensile strength. Explain what this means. ...................................................................................................................................... ..................................................................................................................................[1] resistant to breaking (iii) Explain why graphene has high tensile strength. ...................................................................................................................................... ..................................................................................................................................[1] strong covalent bonds between atoms (iv) Graphene is able to conduct electricity. Explain why. ...................................................................................................................................... ...................................................................................................................................... ..................................................................................................................................[1] each carbon atom contributes one electron delocalise over layer act as mobile charge carrier

3 [Turn over (b) Nickel catalyses a reaction between methane and steam. (i) State the electronic configuration of Ni. 1s2 ............................................................................................................................[1] 1s2 2s2 2p6 3s2 3p6 3d8 4s2 (note: write the electronic configuration in terms of ascending order of the principal quantum shells) (ii) Outline the mode of action as nickel catalyses the reaction between methane and steam. Include bond forming and bond breaking in your answer. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ..................................................................................................................................[3] adsorption of molecules onto nickel surface forming weak interactions with alternative reaction pathway of lower activation energy reactant bonds weaken and break product bonds form desorption of molecules from the surface of the catalyst (iii) The nickel catalyst is made of nanoparticles. Explain what it means by a nanoparticle. ...................................................................................................................................... ..................................................................................................................................[1] all 3 dimensions on the nanoscale of 1 to 100 nm (iv) Explain how nickel being made of nanoparticles would facilitate the catalysis of the reaction. ...................................................................................................................................... ..................................................................................................................................[1] large surface area to volume ratio allows more molecule to bind

4 (c) Methane and steam react to form a mixture of carbon monoxide and hydrogen known as syngas. All four gases exist as an equilibrium mixture. CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ΔH (i) In the carbon monoxide molecule, one of the covalent bonds is a dative bond. Draw the ‘dot -and-cross’ diagram to show the bonding in a molecule of carbon monoxide. (note: dative bond) [1] (ii) Use bond energy values from the Data Booklet to calculate the enthalpy change of the forward reaction, ΔH. ΔH = sum of energies of bonds broken – sum of energies of bonds formed = 4(410) + 2(460) – 1077 – 3(436) = +175 kJ mol–1 (note: enthalpy change requires + sign to be indicated) [2] (iii) In the manufacture of syngas, 1.00 mol of CH4(g) and 1.00 mol of H2O(g) were injected into a 2.00 dm3 reaction chamber at 700 °C. At equilibrium, 0.26 mol of CO(g) was formed. Calculate the equilibrium constant, Kc, for the reaction at 700 °C. Conc. / mol dm–3 CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) I 0.50 0.50 C –0.13 –0.13 +0.13 +0.39 E 0.37 0.37 0.13 0.39 𝐾𝑐 = [𝐶𝑂][𝐻2]3 [𝐶𝐻4][𝐻2𝑂] = (0.13)(0.39)3 (0.37)(0.37) = 0.0563 mol2 dm–6 [2] C O

5 [Turn over (iv) With reference to your answer in (c)(ii), explain how increasing the temperature to 1000 °C would affect the equilibrium position and Kc value. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ..................................................................................................................................[2] equilibrium position shifts right and the value of Kc increases to offset temperature increase by absorbing excess heat energy, favours endothermic reaction. (forward reaction is endothermic) (v) At time t1, the reaction chamber was suddenly compressed such that its volume decreased. Complete the graph below until time t2 to show how the concentrations of CO(g) and H2(g) would change as a result of the sudden compression. [2] both graphs sharply increase, with H2(g) increasing more (due to a higher number of moles). [Sharp increase in concentration as the volume of the chamber was compressed suddenly] both graphs decrease (equilibrium shift left to counter the increase in concentration) with a curve until plateauing before reaching t2, with H 2(g) decreasing more (due to larger number of moles, more reacted) [Total: 19] concentration time 0 t1 H2(g)