Energetics QP.pdf

Questions are for both separate science and combined science students unless indicated in the question 1 A manufacturer investigates some reactions that produce hydrogen....

Questions are for both separate science and combined science students unless indicated in the question 1 A manufacturer investigates some reactions that produce hydrogen. The table shows three possible reversible reactions that he could use. The enthalpy changes are also shown. Reaction Equation ǻH in kJ/mol 1 CH4(g) + 2H2O(g) U CO2(g) + 4H2(g) +165 2 CO(g) + H2O(g) U CO2(g) + H2(g) –41 3 CH4(g) + H2O(g) U CO(g) + 3H2(g) –206 (a) (i) For reaction 1, predict whether the pressure should be low or high to give the greatest yield of products. (1).................................................................................................................................................................................................................................................................................... (ii) Give a reason for your choice. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (b) (i) For reaction 1, predict whether the temperature should be low or high to give the greatest yield of products. (1).................................................................................................................................................................................................................................................................................... (ii) Give a reason for your choice. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ PhysicsAndMathsTutor.com  (c) For reaction 2, suggest why changing the temperature will have less effect on the yield of products than in reactions 1 and 3. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (d) (i) For reaction 3, predict the effect on the rate of the forward reaction of increasing the pressure, without changing the temperature. (1).................................................................................................................................................................................................................................................................................... (ii) Explain your prediction in terms of the particle collision theory. (2)................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (e) The manufacturer makes a batch of ethanoic acid from methanol and carbon monoxide using this reaction. CH3OH + CO o CH3COOH He starts with 64kg of methanol. Calculate the maximum mass of ethanoic acid he could obtain. (3) maximum mass of ethanoic acid =.............................................................. kg (Total for Question 1 = 11 marks) PhysicsAndMathsTutor.com 2 A student burned four liquid fuels in order to compare the amount of energy they released, in the form of heat. She used this apparatus. thermometer copper can water spirit burner liquid fuel The energy released when each fuel was burned was used to raise the temperature of 100 g of water. For each fuel, the student recorded the mass of fuel burned and the increase in temperature of the water. Her results are shown in the table. Average relative Mass of fuel Amount of fuel Increase in Fuel formula mass burned in g burned in mol temperature in qC diesel 170 4 0.024 15 ethanol 46 3 0.065 10 methanol 32 2 0.063 5 petrol 114 1 0.009 4 The best fuel is the one that releases the most energy. (a) The student suggested that petrol was the best fuel. Explain why, using the information in the table. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (b) Another student suggested that diesel was the best fuel. Explain why, using the information in the table. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ PhysicsAndMathsTutor.com  (c) In another experiment, a student burned propanol and then used his results to calculate the energy released when one mole of propanol was burned. He then compared his result with a value from a data book. The values are shown in the table. Energy released per mole of propanol burned in kJ Student’s result 1020 Data book value 2010 Suggest two reasons why the student’s result is lower than the data book value. (2) 1........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ 2........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ PhysicsAndMathsTutor.com  (d) The diagram shows the energy profile for burning a fuel. A energy C reactants B products Which of the energy changes A, B or C represents t UIF BDUJWBUJPO FOFSHZ GPS UIF SFBDUJPO t UIF BNPVOU PG FOFSHZ HJWFO PVU EVSJOH UIF SFBDUJPO (separate only) (2) Activation energy =............................................................................................................................................................................................................................ Energy released =................................................................................................................................................................................................................................. (e) Explain, in terms of bond breaking and bond making, why this reaction gives out energy. (separate only) (3).................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... (Total for Question 2 = 9 marks) PhysicsAndMathsTutor.com 3 A student draws this diagram to show how he plans to prepare and collect oxygen gas in a laboratory. manganese(IV) oxide oxygen water hydrogen peroxide (a) The student makes a mistake in the labelling. He also misses out a piece of apparatus. (i) State the mistake in the labelling of the diagram. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (ii) Identify the piece of apparatus missing from the diagram. (1).................................................................................................................................................................................................................................................................................... (iii) State why this piece of apparatus is necessary. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (b) The student adds the missing piece of apparatus, then collects some oxygen gas. This oxygen gas contains water vapour. Suggest how he could alter the apparatus so that he could collect dry oxygen gas. (1)........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ PhysicsAndMathsTutor.com  (c) Balance the equation for the reaction used in this preparation of oxygen. (1)........................ H2O2 o........................ H2 O +........................ O2 (d) The manganese(IV) oxide acts as a catalyst. What is meant by the term catalyst? (2)................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ (e) The diagram shows the reaction profile for the decomposition of hydrogen peroxide without a catalyst. hydrogen peroxide energy water + oxygen (i) Label the diagram to show the activation energy (Ea) for this reaction. (separate only) (1) (ii) On the diagram, draw a curve to represent the reaction profile for the same reaction when a catalyst is used. (separate only) (1) (Total for Question 3 = 9 marks) PhysicsAndMathsTutor.com 4 The equation for a reaction that occurs in the manufacture of nitric acid is 4NH3(g) + 5O2(g) U

4NO(g) + 6H2O(g) ǻH = −900 kJ/mol (a) (i) State the meanings of the symbols U and ǻH. (2) U
........................................................................................................................................................................................................................................................................... ǻH.......................................................................................................................................................................................................................................................................... (ii) What does the negative sign of ǻH indicate about the reaction? (1).................................................................................................................................................................................................................................................................................... (b) Complete the energy level diagram for this reaction. (separate only) (2) Energy (c) Typical conditions used for this reaction are a temperature of 900 °C and a pressure of 10 atmospheres. Deduce the effects of changing the conditions as shown in the table. Choose from the words increased, decreased or unchanged to complete the table. (4) Change Effect on rate of reaction Effect on yield of products increase in temperature addition of catalyst PhysicsAndMathsTutor.com  (d) A manufacturer considers using a pressure of 5 atm instead of 10 atm. (i) Predict and explain the effect on the rate of reaction of changing the pressure to 5 atm. (3) Effect on rate of reaction................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... Explanation.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................. (ii) Predict and explain the effect on the position of equilibrium of changing the pressure to 5 atm. (separate only) (2) Effect on position of equilibrium.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................. Explanation.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... (e) Balance the equation that represents the last stage in the manufacture of nitric acid..................... NO2 +.................... O2 +.................... H2O o.................... HNO3 (1) (Total for Question 4 = 15 marks) PhysicsAndMathsTutor.com