RI 2021 Chem Y4 WS Equilibrium Assignment Answer

RAFFLES GIRLS’ SCHOOL (SECONDARY) RAFFLES PROGRAMME CHEMISTRY YEAR 4 Name : _______________________ ( ) Class : _______ Date : ________________ 1 Established in 1879 CHEMICAL EQUILIBRIUM Assignment 1. The Haber process involves the extraction of hydrogen, extraction of nitrogen and combination of hydrogen and nitrogen to make ammonia. (a) State how nitrogen is extracted to make ammonia. It is obtained from the fractional distillation of liquid air. (b) State a suitable catalyst for the Haber process. Iron catalyst (c) According to the graph, what are the optimum conditions to produce the maximum yield of ammonia? 350oC and 400 atmospheres. % yield of ammonia Pressure / atm 70 60 50 40 30 20 10 0 0 100 200 300 400 350 °C 400 °C 450 °C 500 °C 550 °C This study source was downloaded by 100000857398866 from CourseHero.com on 11-15-2024 00:01:14 GMT -06:00 https://www.coursehero.com/file/219781819/2021-Chem-Y4-WS-Equilibrium-Assignment-Answer-F7uyr-evZ-2pdf/

2 (d) According to the graph, how does temperature and pressure affect the % yield of ammonia? As temperature increases, the percentage yield of ammonia decreases. As pressure increases, the percentage yield of ammonia increases. (e) Sketch on the graph above the curve showing the % yield of ammonia at 450oC. (f) Explain why the typical conditions of 200 atmospheres and 450oC are used for the Haber process in the industries. Even though low temperature gives higher yield of ammonia, decreasing the temperature too much would result in a slower reaction. 450°C is a compromise temperature producing a reasonably high yield of ammonia but in a very short time. Even though high pressure gives higher yield of ammonia, high pressure is very expensive to produce. 200 atmospheres is a compromise pressure, producing a reasonable high yield of ammonia without investing too high a capital cost to maintain too high a pressure. 5 This study source was downloaded by 100000857398866 from CourseHero.com on 11-15-2024 00:01:14 GMT -06:00 https://www.coursehero.com/file/219781819/2021-Chem-Y4-WS-Equilibrium-Assignment-Answer-F7uyr-evZ-2pdf/

3 2. (Adapted from O Level 2018 P2A Q6) The process of making ammonia from raw materials has several stages. The equations show two stages in the process. Stage 1: Methane reacts with steam to make hydrogen. CH4(g) + H2O(g) ⇌ CO(g) + 3 H2(g) ΔH = +210 kJ/mol Stage 2: The hydrogen formed reacts with nitrogen to make ammonia in a reactor. N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = −92 kJ/mol (a) Less energy is needed to maintain the temperature for stage 2 than is needed for stage 1. Suggest two reasons why the reaction in stage 2 requires less energy. The temperature used for Stage 2 (450 °C) is lower than that used in Stage 1 (800 °C), thus less energy is needed for Stage 2. Stage 2 is an exothermic reaction which gives off heat energy to the surroundings, helping to maintain the temperature, while Stage 1 is an endothermic reaction which requires heat to be absorbed from the surroundings, which requires more energy to be supplied. (b) The gases from stage 1 are separated. The waste gas produced in stage 1 is burned as a fuel. Explain why it is important that this gas is collected and burned. The waste gas carbon monoxide is a toxic gas that is harmful to human health as it binds with haemoglobin in the blood, preventing transport of oxygen to the body. Burning carbon monoxide produces carbon dioxide which is relatively harmless. (c) In stage 2, nitrogen and hydrogen are mixed in definite proportions before they enter the reactor. The table shows the percentages of each gas in the mixture by volume and by mass. nitrogen hydrogen percentage by volume 25 75 percentage by mass 82 18 Conditions: 30 atm nickel oxide catalyst 800 °C Conditions: 25 – 150 atm iron catalyst 450 °C This study source was downloaded by 100000857398866 from CourseHero.com on 11-15-2024 00:01:14 GMT -06:00 https://www.coursehero.com/file/219781819/2021-Chem-Y4-WS-Equilibrium-Assignment-Answer-F7uyr-evZ-2pdf/

4 (i) Explain why these percentages by volume are chosen. The percentage by volume reduces to 1:3 which is the same as the stoichiometric / mole ratio given by the chemical equation. (ii) Explain why the percentages of the gases are different when they are measured by volume and when they are measured by mass. The molar volume of a gas is 24 dm3/mol for both nitrogen and hydrogen, while the molar masses of the two gases are different. Nitrogen has a molar mass of 28 g/mol while hydrogen has a molar mass of 2 g/mol. (iii) The gases leaving the reactor contain unreacted nitrogen and hydrogen and about 15% ammonia by volume. Unreacted nitrogen and hydrogen are fed back into the reactor in stage 2. Give two reasons why the unreacted gases are fed back into the reactor. Feeding back the unreacted gasses allows them to be reused, saving cost and preventing wastage. This also improves the yield of ammonia produced. This study source was downloaded by 100000857398866 from CourseHero.com on 11-15-2024 00:01:14 GMT -06:00 https://www.coursehero.com/file/219781819/2021-Chem-Y4-WS-Equilibrium-Assignment-Answer-F7uyr-evZ-2pdf/ Powered by TCPDF (www.tcpdf.org)