6. Chemical reactions
A section of Chemistry, 0620
Listing 10 of 905 questions
Ammonia is an important chemical. Ammonia is a base. In chemistry, what is meant by the term base? Write a word equation to show ammonia behaving as a base. Ammonia reacts with chlorine. The chemical equation is shown. 2NH3+ 3Cl 2N2+ 6HCl Calculate the volume of chlorine, measured at room temperature and pressure, needed to react completely with 0.68 g of ammonia.  volume of chlorine = cm3 The chemical equation can be represented as shown. H H H + + Cl Cl N N N Cl H Use the bond energies in the table to determine the energy change, ΔH, for the reaction between ammonia and chlorine. bond bond energy in kJ / mol N–H Cl –Cl N≡N H–Cl ● ● energy needed to break bonds  kJ ● ● energy released when bonds are formed  kJ ● ● energy change, ΔH, for the reaction between ammonia and chlorine  kJ  Is the reaction endothermic or exothermic? Explain your answer. Ammonia reacts with oxygen at high temperatures in the presence of a suitable catalyst to form nitricoxide, NO. 4NH3+ 5O24NO+ 6H2OExplain how this chemical equation shows ammonia acting as a reducing agent. Suggest a suitable catalyst for the reaction from the list of metals. Give a reason for your answer. aluminium calcium platinum potassium sodium suitable catalyst reason  
0620_m18_qp_42
THEORY
2018
Paper 4, Variant 2
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The Haber process is used to manufacture ammonia. State the main source of each gas used in the Haber process. nitrogen hydrogen  The equation for the Haber process is shown. N2+ 3H22NH3∆H = –92 kJ / mol The reaction is reversible. The forward reaction is exothermic. State what is meant by the symbol ∆H. ∆H for the forward reaction is –92 kJ / mol. State why this value shows that the forward reaction is exothermic. State the typical conditions and name the catalyst used in the Haber process. temperature °C pressure kPa catalyst  Complete Table3.1 to show the effect, if any, when the typical conditions in the Haber process are changed. Use only the words increases, decreases or no change. Table 3.1 change to typical conditions effect on the rate of the forward reaction effect on the concentration of NH3at equilibrium temperature increases increases pressure decreases no catalyst decreases  Explain in terms of collision theory why increasing the temperature increases the rate of the reaction. Ammonia reacts with an acid to form ammoniumsulfate, (NH4)2SO4. State the formula of the acid used. State one use of ammonium sulfate. Calculate the percentage composition by mass of nitrogen in (NH4)2SO4.  percentage of nitrogen = % 
0620_m23_qp_42
THEORY
2023
Paper 4, Variant 2
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Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible. 2HII2+ H2colourless gas purple gas colourless gas shows a gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases. The gas syringe is sealed and the mixture is heated to 300 °C. The mixture of gases reaches equilibrium and is purple. end sealed plunger equilibrium mixture of hydrogen iodide, iodine and hydrogen State what is meant by the term equilibrium. The pressure of the mixture is increased. All other conditions stay the same. The position of equilibrium does not change. The colour of the gaseous mixture turns darker purple. The temperature remains constant. 2HII2+ H2colourless gas purple gas colourless gas Explain why the position of equilibrium does not change. Suggest why the colour of the mixture of gases turns darker purple. The temperature of the mixture of gases is decreased. All other conditions stay the same. The mixture of gases turns lighter purple. State what can be deduced about the forward reaction from this information. Deduce the oxidation number of iodine, I, in: HI I2.  Methanol is manufactured by reacting carbon monoxide with hydrogen. CO+ 2H2CH3OHThe rate of formation of methanol increases when a catalyst is used. Choose from the list the element that is most likely to be used as the catalyst. Draw a circle around your chosen answer. calcium carbon copper sodium sulfur State the effect on the position of equilibrium when a catalyst is used. State the effect that a catalyst has on the activation energy, Ea, of a reaction. 
0620_s24_qp_41
THEORY
2024
Paper 4, Variant 1
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The symbol equation for the industrial production of ammonia is shown. N2+ 3H22NH3∆H = –90 kJ / mol Name this industrial process. State the meaning of ∆H. State the typical conditions and name the catalyst used in the industrial production of ammonia. temperature and units pressure and units catalyst used State two methods of increasing the rate of this reaction. The symbol equation for the reaction can be represented as shown in . N N + +  H H = –90 kJ / mol H H N H H H N H H H H H H Table 3.1 shows some bond energies. Table 3.1 bond N≡N H–H bond energy in kJ / mol Use the bond energies in Table 3.1 and ∆H to calculate the bond energy of an N–H bond, in kJ / mol. Use the following steps. ● Calculate the energy needed to break bonds in the reactants. kJ ● Calculate the energy released when bonds form in the products. kJ ● Calculate the energy of an N–H bond. kJ / mol ,  , An incomplete symbol equation for the preparation of ammonia in the laboratory is shown. CaO + 2NH4Cl → CaCl 2 + + 2NH3 Complete the symbol equation. Name NH4Cl. Calculate the volume of ammonia, NH3, measured at room temperature and pressure, which forms when 1.12 g of CaO is heated with excess NH4Cl. [Mr: CaO, 56] cm3 ,  ,
0620_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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Sulfuric acid is made by the Contact process. Sulfur is burned by spraying droplets of molten sulfur into air. Suggest and explain an advantage of using this method. The following equation represents the equilibrium in the Contact process. 2SO2+ O22SO3Oxygen is supplied from the air. The composition of the reaction mixture is 1 volume of sulfur dioxide to 1 volume of oxygen. What volume of air contains 1 dm3 of oxygen? dm3 Sulfur dioxide is more expensive than air. What is the advantage of using an excess of air? The forward reaction is exothermic. The reaction is usually carried out at a temperature between 400 and 450 °C. What is the effect on the position of equilibrium of using a temperature above 450 °C? Explain your answer. What is the effect on the rate of using a temperature below 400 °C? Explain your answer. A low pressure, 2 atmospheres, is used. At equilibrium, about 98% SO3 is present. What is the effect on the position of equilibrium of using a higher pressure? Explain why a higher pressure is not used. Name the catalyst used in the Contact process. Describe how concentrated sulfuric acid is made from sulfur trioxide.
0620_w15_qp_31
THEORY
2015
Paper 3, Variant 1
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Questions Discovered
905