Higher Chemistry Principles to Production October Revision

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1 igher Chemistry Principles to Production October Revision You should use your class notes, Evans2Chemweb and Scholar to help. Show your working for each question. Sections covered so far; Principles to Production Getting the most from costly reactants Factors influencing the design of an industrial process Calculation of mass or volume of products assuming complete conversion Reversible reactions Altering equilibrium position Percentage yield and atom economy Excess Controlling the rate Collision theory Reaction profiles Temperature and kinetic energy Catalysts Chemical Energy Enthalpy Enthalpies of combustion ess s law Bond enthalpies Still to cover in this unit; Chemical analysis as part of quality control Chromatography Volumetric titration

2 Reaction rates

4 Efficiency of Production If we take the production of ammonia for example: N 2(g) + 3 2(g) 2N 3(g) 1. What is a cheap and environmentally friendly source of nitrogen? 2. As this is an equilibrium reaction only about 17% of the reactants are converted into products, how does the process reduce the amount of waste reactants being lost. 3. The reaction is carried out at approximately C, but is an exothermic reaction, suggest a way that the process reduces the energy requirements of the plant and thus reduces their carbon footprint? 4. Suggest why cooling the equilibrium mixture in a condenser, to liquefy the ammonia gas, produces a higher yield of product?

5 Using an equation to calculate costs 39g of CaF 2 and 500g of 2 SO 4 made 24 litres of hydrogen fluoride. Calculate the cost of chemicals needed to make 50,000 litres of hydrogen fluoride. (The costs of the chemicals are shown below) Calcium Fluoride Sulphuric acid 9 for 1kg 55 for 1000kg

6 Enthalpy change 1 2

7 ess s Law 1 Calculate the following enthalpy change using enthalpies of combustion in your data book: 4C (s) + 5 2(g) C 4 10(g) 2. From the enthalpies of combustion in your data book calculate the enthalpy for the following reaction between ethyne and hydrogen to make ethane: C (g) C 2 6(g) 3. Using the enthalpies of combustion in your data book, calculate the enthalpy of formation of cyclopentane (C 5 10 ). 5C (s) + 5 2(g) C 5 10(l) The enthalpy of combustion of cyclopentane is kjmol When in danger, bombardier beetles can fire a hot, toxic mixture of chemicals at the attacker. This mixture contains quinone, C 6 4 O 2, a compound that is formed by the reaction of hydroquinone, C 6 4 (O) 2, with hydrogen peroxide, 2 O 2. The reaction is catalysed by an enzyme called catalase. The equation for the overall reaction is: C 6 4 (O) 2 (aq) + 2 O 2 (aq) C 6 4 O 2 (aq) O(l) Use the following data to calculate the enthalpy change, in kj mol -1, for the above reaction. C 6 4 (O) 2 (aq) C 6 4 O 2 (aq) + 2 (g) = kJ mol -1 2 (g) + O 2 (g) 2 O 2 (aq) = kJ mol -1 2 (g) + ½O 2 (g) 2 O(g) = kJ mol -1 2 O(g) 2 O(l) = -43.8kJ mol -1

8 Bond enthalpies (The first one has been done for you) 1. Calculate the enthalpy change for the combustion of hydrogen to produce water shown by the equation below using bond enthalpies. 2 2 (g) + O 2 (g) 2 2 O (g) O + O O O Bond Breaking Bond Making 2 mol - = 2 x 432 = mol -O = 4 x 458 = mol O=O = 497 Total energy put in = kj Total energy given out = kj = = -471 kjmol Use bond enthalpy values from the data book to calculate the enthalpy change for the following reaction. C 4 (g) + Br 2 (g) C 3 Br (g) + Br (g) 3. The data book gives the enthalpy of combustion of ethanol as kjmol -1. Use bond enthalpies to calculate the enthalpy change for this reaction. C 2 5 O (g) + 3O 2 (g) 2CO 2 (g) O (g)

9 Molar Volume Calculations (1) 2NO (g) + O 2(g) 2NO 2(g) ow many litres of dinitrogen dioxide could be obtained by mixing 1.5 litres of nitrogen monoxide and 0.5 litres of oxygen? A mixture of 20cm 3 of methane and 30cm 3 of oxygen were ignited at 130 C. (a) Which reactant was in excess and by how much? (hint balanced equation needed) (b) What volume of water vapour was produced? Calculate the volume of carbon dioxide released when 0.4g of calcium carbonate is dissolved in excess hydrochloric acid. (molar Volume 24 l) (int: you need a balanced equation.) Percentage Yield and Atom economy 1. C 3 O + C 2 5 COO C 2 5 COOC O methanol ethanoic acid methylethanoate In preparation, 15g of methylethanoate is made from 20g of methanol. a. Calculate the % yield. b. Calculate the atom economy for this reaction. 2. Nitrous oxide NO can be made by the catalytic oxidation of ammonia: 2N 3(g) + 2.5O 2(g) 2NO (g) O (g) i. What is the % yield of nitrous oxide if 340g of ammonia gas produces 500g of nitrous oxide? ii. Calculate the atom economy for this reaction.

10 1 Copy and complete the table Equilibrium Variable Change Side of reaction favoured Concentration of reactants Concentration of reactants Concentration of products Concentration of products Pressure Increase Increase Reactants Products Side with fewest gaseous molecules Pressure Side with most gaseous molecules Temperature Increase direction Temperature Decrease direction 2. In which of the reactions will the equilibrium be unaffected by a change in pressure? A. B. C. D. 3. Which two conditions favour the formation of NO 2? A B C D. igh temperature, high pressure igh temperature, low pressure Low temperature, high pressure Low temperature, low pressure

11 1. igher Chemistry Principles to Production Extra calculations The production of hydrogen bromide is exothermic. 2 + Br 2 2Br Using bond enthalpies calculate the enthalpy change in kjmol -1 for this reaction. Extra questions to try if you have time 2. Sodium carbonate can be made in the following reaction. Methane is produced as a by-product. a. b. c. NaO + C 3 COONa C 4 + Na 2 CO 3 Calculate the % atom economy for the production of sodium carbonate using this reaction. In industry 5 Kg of sodium hydroxide made 10 Kg of sodium carbonate. Calculate the percentage yield for this reaction, assuming the C 3 COONa is in excess. NaO is 2.10 per kg, and sodium ethanoate is 0.45 per 100g. If 5 Kg of sodium hydroxide and 11Kg of sodium ethanoate make 10Kg of sodium carbonate, how much would it cost to make 1000Kg of sodium carbonate? 3. In the lab, nitrogen dioxide gas can be prepared by heating copper (II) nitrate. Cu(NO 3 ) 2(s) CuO (s) + 2NO 2(g) +½O 2(g) Calculate the volume of nitrogen dioxide gas produced when 2.0 g of copper (II) nitrate is completely decomposed on heating. (Take molar volume of NO 2 to be 24 litres mol -1 ) 4. A student was preparing hydrogen gas. She added 2.0g of magnesium ribbon to 100cm 3 of 0.5moll -1 hydrochloric acid. Mg + 2Cl MgCl Show by calculation which reactant was in excess. Answers: kJmol -1 (a) 86.9% (b) 75.5% (c) litres 4. Mg in xs by moles

The table below includes some values of standard enthalpies of formation ( H ).

The table below includes some values of standard enthalpies of formation ( H ). 1. A vessel and its contents of total heat capacity 120 J K 1 were heated using a methane burner. Calculate the maximum theoretical temperature rise when 0.10 g of methane was completely burned. The standard