6. Chemical reactions
A section of Chemistry, 0620
Listing 10 of 905 questions
Acids have characteristic properties. Hydrochloricacid reacts with magnesium. Name the products of this reaction and give the observations. The rate of reaction of iron(carbonate with hydrochloricacid can be determined by measuring the time taken to produce 20 cm3 of carbondioxide. A student measured the time taken to produce 20 cm3 of carbon dioxide at three different temperatures. In each experiment the student used: ● ● 1 g of large pieces of iron(carbonate ● ● dilute hydrochloric acid of the same concentration and volume. The results are shown in the table. temperature / °C time / s Use the information in the table to describe how the rate of reaction changes with temperature. Describe the effect of each of the following on the rate of this reaction at constant temperature. ● ● Smaller pieces of iron(carbonate are used. All other conditions stay the same. ● ● The concentration of hydrochloricacid is decreased. All other conditions stay the same.  The reaction of iron(carbonate with hydrochloricacid is exothermic. What is meant by the term exothermic? Rust contains compounds of iron. State two conditions needed for iron to rust. Iron and magnesium are both used in alloys. Which one of these diagrams, A, B, C or D, best represents an alloy? A B C D 
0620_s20_qp_31
THEORY
2020
Paper 3, Variant 1
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Acids have characteristic properties. Hydrochloric acid reacts with magnesiumcarbonate. Name the products of this reaction and give the observations. The rate of reaction of iron with sulfuricacid can be determined by measuring the time taken to produce 20 cm3 of hydrogen. A student measured the time taken to produce 20 cm3 of hydrogen using three different concentrations of sulfuricacid. In each experiment the student used: ● ● 1 g of iron powder ● ● the same temperature ● ● the same volume of sulfuric acid. The results are shown in the table. concentration of acid in mol / dm3 time / s 0.1 0.2 0.5 Use the information in the table to describe how the rate of reaction changes with the concentration of sulfuricacid. Describe the effect of each of the following on the rate of this reaction with 0.5 mol / dm3 of sulfuricacid. ● ● Larger pieces of iron are used. All other conditions stay the same. ● ● The temperature is increased. All other conditions stay the same.  Heat is given out when iron reacts with sulfuricacid. What term describes a reaction which gives out heat? The reaction of iron with steam is shown. 3Fe + 4H2O → Fe3O4 + 4H2 How does this equation show that iron gets oxidised? Rust contains hydrated iron(oxide. Describe and explain one method of preventing iron from rusting. 
0620_s20_qp_32
THEORY
2020
Paper 3, Variant 2
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Oxygen is produced by the decomposition of hydrogen peroxide. Manganese(oxide is the catalyst for this reaction. What is meant by the term catalyst ? A student measures the volume of oxygen produced at regular time intervals using the apparatus shown. Large lumps of manganese(oxide are used. aqueous hydrogen peroxide gas syringe manganese(oxide catalyst A graph of the results is shown. volume of oxygen produced / cm3 time / s What happens to the rate of this reaction as time increases? In your answer, explain why the rate changes in this way. The experiment is repeated using the same mass of manganese(oxide. Powdered manganese(oxide is used instead of large lumps. All other conditions stay the same. Sketch a graph on the axes in to show how the volume of oxygen changes with time. In terms of particles, explain what happens to the rate of this reaction when the temperature is increased. The equation for the decomposition of hydrogen peroxide is shown. 2H2O2→ 2H2O+ O225.0 cm3 of aqueous hydrogenperoxide forms 48.0 cm3 of oxygen at room temperature and pressure (r.t.p.). Calculate the concentration of aqueous hydrogenperoxide at the start of the experiment using the following steps. ● ● Calculate the number of moles of oxygen formed.  mol ● ● Deduce the number of moles of hydrogen peroxide that decomposed.  mol ● ● Calculate the concentration of hydrogen peroxide in mol / dm3.  mol / dm3  Oxygen can also be produced by the decomposition of potassiumchlorate(, KCl O3. The only products of this decomposition are potassiumchloride and oxygen. Write a chemical equation for this decomposition. 
0620_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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Ammonia is manufactured by the Haber process. The equation for the reaction is shown. N2+ 3H22NH3State what is meant by the symbol . State one source of hydrogen used in the manufacture of ammonia. The table shows some data for the production of ammonia. pressure / atm temperature / °C percentage yield of ammonia Deduce the effect on the percentage yield of ammonia of: ● ● increasing the pressure of the reaction ● ● increasing the temperature of the reaction.  Explain, in terms of particles, what happens to the rate of this reaction when the temperature is increased. Ammonia, NH3, is used to produce nitricacid, HNO3. This happens in a three-stage process. Stage1 is a redox reaction. 4NH3 + 5O2 → 4NO + 6H2O Identify what is oxidised in stage1. Give a reason for your answer. substance oxidised reason  In this reaction the predicted yield of NO is 512 g. The actual yield is 384 g. Calculate the percentage yield of NO in this reaction.  percentage yield of NO = The equation for the reaction in stage2 is shown. 2NO + O2 → 2NO2 Which major environmental problem does NO2 cause if it is released into the atmosphere? The equation for the reaction in stage3 is shown. 4NO2 + 2H2O + O2 → 4HNO3 Calculate the volume of O2 gas, at room temperature and pressure (r.t.p.), needed to produce 1260 g of HNO3. Use the following steps. ● ● Calculate the number of moles of HNO3.  moles of HNO3 = ● ● Deduce the number of moles of O2 that reacted.  moles of O2 = ● ● Calculate the volume of O2 gas that reacts at room temperature and pressure (r.t.p.).  volume of O2 gas = dm3  The reaction in stage3 is exothermic. 4NO2 + 2H2O + O2 → 4HNO3 Complete the energy level diagram for this reaction. Include an arrow that clearly shows the energy change during the reaction. energy progress of reaction 4NO2 + 2H2O + O2  
0620_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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905