6.3. Reversible reactions and equilibrium
A subsection of Chemistry, 0620, through 6. Chemical reactions
Listing 10 of 390 questions
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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Dinitrogen tetroxide, N2O4, decomposes into nitrogen dioxide, NO2.The reaction is reversible. N2O42NO2colourless gas brown gas shows a gas syringe containing a mixture of dinitrogen tetroxide and nitrogen dioxide. The gas syringe is sealed. The mixture reaches equilibrium and the colour of the mixture of gases is a pale brown. end sealed plunger mixture of dinitrogen tetroxide and nitrogen dioxide Describe a reversible reaction at equilibrium in terms of: ● the rate of the forward reaction and the rate of the reverse reaction ● the concentration of reactants and products.  The pressure of the mixture is increased. All other conditions stay the same. The mixture immediately turns darker brown before the position of equilibrium changes. Explain in terms of particles why the mixture immediately turns darker brown. The temperature of the mixture is increased. All other conditions stay the same. The mixture turns darker brown. State what can be deduced about the forward reaction from this information. Sulfur is converted into sulfuric acid, H2SO4, by a series of reactions. Sulfur dioxide, SO2, and oxygen, O2, react to form sulfur trioxide, SO3. The reversible reaction reaches equilibrium. 2SO2+ O22SO3Complete Table 4.1 using only the words, increases, decreases or no change. Table 4.1 effect on the rate of the forward reaction effect on the equilibrium yield of SO3add a catalyst increase the pressure  Deduce the oxidation number of sulfur in: S SO3  
0620_s24_qp_43
THEORY
2024
Paper 4, Variant 3
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For Examiner's Use Sulfuric acid is made by the Contact process. 2SO2 + O2 2SO3 This is carried out in the presence of a catalyst at 450 °C and 2 atmospheres pressure. How is the sulfur dioxide made? Give another use of sulfur dioxide. Name the catalyst used. If the temperature is decreased to 300 °C, the yield of sulfur trioxide increases. Explain why this lower temperature is not used. Sulfur trioxide is dissolved in concentrated sulfuric acid. This is added to water to make more sulfuric acid. Why is sulfur trioxide not added directly to water? For Examiner's Use Sulfuric acid was first made in the Middle East by heating the mineral, green vitriol, FeSO4.7H2O. The gases formed were cooled. FeSO4.7H2O→ FeSO4+ 7H2Ogreen crystals yellow powder 2FeSO4→ Fe2O3+ SO2+ SO3On cooling SO3 + H2O → H2SO4 sulfuric acid SO2 + H2O → H2SO3 sulfurous acid How could you show that the first reaction is reversible? Sulfurous acid is a reductant. What would you see when acidified potassium manganate(is added to a solution containing this acid? Suggest an explanation why sulfurous acid in contact with air changes into sulfuric acid. 9.12 g of anhydrous iron(sulfate was heated. Calculate the mass of iron(oxide formed and the volume of sulfur trioxide, at r.t.p., formed. 2FeSO4→ Fe2O3+ SO2+ SO3mass of one mole of FeSO4 = 152 g number of moles of FeSO4 used = number of moles of Fe2O3 formed = mass of one mole of Fe2O3 = g mass of iron(oxide formed = g number of moles of SO3 formed = volume of sulfur trioxide formed = dm3
0620_w09_qp_31
THEORY
2009
Paper 3, Variant 1
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Questions Discovered
390