Beatty 16.1 AMMONIA (W1) 2023 Answers

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E___ TOPIC: AMMONIA (WORKSHEET 1) Learning Objectives: (a) State that some chemical reactions are reversible, e.g. manufacture of ammonia. (b) Describe the use of nitrogen, from air, and hydrogen, from the cracking of crude oil, in the manufacture of ammonia. (c) Describe the essential conditions for the manufacture of NH3 by the Haber process. (d) Describe the use of ammonia to manufacture nitrogenous fertilisers. (e) Describe the displacement of ammonia from its salts and explain why adding calcium hydroxide to soil can cause the loss of nitrogen from added nitrogenous fertiliser. Multiple-Choice Questions 1 The catalyst used in the Haber process is ____________. A copper B iron C hydrogen chloride D nickel ( B ) 2 When 1 mol of nitrogen is reacted with 3 mol of hydrogen a t 250 atm and 450 °C in the presence of an iron catalyst, less than 2 mol of ammonia is formed. Which of the following best explains this observation? A The pressure used was too low. B The temperature used was too low. C The nitrogen and hydrogen used in the reaction contained impurities. D The reaction of nitrogen and hydrogen to form ammonia is reversible. ( D ) 3 Which ion will react with ammonium sulfate to give ammonia gas? A NH4+ B OH– C H+ D Cl– ( B ) 4 All ammonium salts on h eating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained? A 0.5 mol (NH4)3PO4 B 0.5 mol (NH4)2SO4 C 1.0 mol NH4Cl D 1.0 mol NH4NO3 ( A )

2 5 Which of the following will not react with ammonium salts to give ammonia gas? A limewater B potassium hydroxide C hydrochloric acid D sodium hydroxide ( C ) Use the following information to answer Questions 6 and 7. The Haber process is used to manufacture ammonia gas. The reactio n is exothermic and the chemical equation for the process is: N2(g) + 3H2(g) ⇌ 2NH3(g) 6 Given that the same volumes of nitrogen and hydrogen was used, what is the effect of increasing the pressure inside the reaction vessel on the rate of production and the overall yield of ammonia gas? rate yield A decrease decrease B increase unchanged C increase decrease D increase increase ( B ) 7 Which of the following statements is not true of the Haber process? A The raw material, nitrogen gas, is obtained from the cracking of petroleum. B Liquid ammonia is the product of the Haber process. C Nitrogen and hydrogen gases are compressed at 250 atm during the process. D Unreacted nitrogen and hydrogen are recycled and transferred back into the converter. ( A ) 8 Ammonia is produced by the reaction of the e lements hydrogen and nitrogen in the Haber process. One of these elements is obtained from crude oil. The ammonia formed can be reacted with substance Q to form a salt. Ammonia can be displaced from this salt by reacting with substance R. Which row co rrectly shows the element obtained from crude oil and the types of substances corresponding to Q and R? element obtained from crude oil substance Q substance R A hydrogen acid base B hydrogen base acid C nitrogen acid base D nitrogen base acid ( A )

3 9 Which of the following statements are true of the Haber process? 1 An increase in pressure increases the speed of reaction. 2 An iron catalyst is used to increase the yield of ammonia. 3 A high temperature of 450 °C is used to increase the yield of ammonia. 4 A relatively low pressure of 250 atm is used because it is costly to maintain a high pressure. A 1 and 4 B 1, 3 and 4 C 2 and 3 D 1, 2, 3 and 4 ( A ) 10 Which conditions are ideal for the manufacture of ammonia in the Haber process? pressure / atm temperature / °C ratio of hydrogen : nitrogen A 250 450 3 : 1 B 250 450 1 : 3 C 450 250 3 : 1 D 450 250 1 : 3 ( A ) 11 Which fertiliser provides the most nitrogen per mole? A NH4NO3 B NaNO3 C (NH4)3PO4 D (NH4)2SO4 ( C ) 12 Hydrazine has the formula, H 2NNH2. It has similar properties to ammonia. Which property will hydrazine have? A It dissolves in water to give hydrogen ions. B It is an ionic compound. C It reacts with alkalis to form salts. D It reacts with hydrogen chloride to form a compound with the formula ClH3NNH3Cl. ( D ) 13 The fertiliser ammonium nitrate (NH 4NO3, M r = 80) is manufactured from ammonia (NH3, Mr = 17) by a two-stage process. Stage 1 NH3 + 2O2 → HNO3 + H2O Stage 2 HNO3 + NH3 → NH4NO3 What is the maximum mass of fertiliser that can be made if only 17 tonnes of ammonia is available? A 17 tonnes B 40 tonnes C 80 tonnes D 97 tonnes ( B )

4 Structured Questions 14 Ammonia is produc ed commercially by the Haber process. T he graph shows the percentage yield of ammonia at different pressures and temperatures. (a) How does pressure affect the yield of ammonia? The higher the pressure, the higher the percentage yield of ammonia. (b) How does temperature affect the yield of ammonia? The higher the temperature, the lower the percentage yield of ammonia. (c) What happens to the speed of reaction when the temperature is lowered? The speed of reaction decreases when the temperature is lowered (d) Why is the temperature used in the Haber process usually around 450 °C and not higher? A higher temperature greater than 450 °C would lead to a decrease in the percentage yield of ammonia as the products would thermally decompose to form back nitrogen and hy drogen reactants. (e) Based on the graph, what will be the percentage of ammonia formed at 450 °C and 200 atm? Around 35.0% 15 The production of ammonia from nitrogen and hydrogen is a reversible reaction. (a) What do you understand by the term reversible reaction? A reversible reaction is a r eaction whereby the reactants, N2 and H2, can react to undergo a forward reaction to form the product, NH3, and the product, NH 3, can dissociate to undergo a backward reaction to form N2 and H2 at the same time.

5 (b) Given that the ∆H = −92 kJ/mol for the produ ction of ammonia , is the decomposition of ammonia to nitrogen and hydrogen an exothermic or endothermic process? Explain your answer. Endothermic. The enthalpy change for the reverse reaction would have a positive value of +92.0 kJ/mol. (c) With the aid of an equation, explain why the volume of hydrogen to nitrogen gas used is 3:1. N2 (g) + 3H2 (g) ⇌ 2NH3 (g) According to the equation, 1 mole of nitrogen requires 3 moles of hydrogen to react together. Since 1 mole of any gas has the same volume at room temperature and pressure. Thus, based on Avogadro’s Law, 1 volume of nitrogen requires 3 volumes of hydrogen to react together. (d) When the mixture of hydrogen, nitrogen and ammonia enters the cooler, the ammonia turns into a liquid, but the other gases do not. What does this tell you about the boiling point of ammonia? The boiling point of ammonia is higher than hydrogen and nitrogen. 16 Ammonia is used to manufacture nitric acid, by a two-stage process. Stage 1: the ammonia is converted to nitrogen monoxide. 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) Stage 2: the nitrogen monoxide is converted to nitric acid 4NO(g) + 2H2O(g) + 3O2(g) → 4HNO3(aq) (a) Explain why stage 2 is a redox process. Oxygen in O2 is reduced to HNO3 and nitrogen in NO is oxidised to HNO3 at the same time. Oxidation state of O decreases from 0 in O2 to −2 in HNO3 while oxidation state of N increases from +2 in NO to +5 in HNO3. (b) Determine the percentage yield of nitric acid, if