8. Reaction kinetics
A section of Chemistry, 9701
Listing 10 of 220 questions
A chemist puts a sample of dilute aqueous hydrochloric acid into beaker 1. She adds a sample of zinc and measures the rate of production of hydrogen gas. She then puts a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate of production of hydrogen gas. The rate of the reaction in beaker 2 is greater than the rate of the reaction in beaker 1. Which factors could help to explain this observation?
9701_m16_qp_12
MCQ
2016
Paper 1, Variant 2
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Chlorine dioxide undergoes the following reaction in aqueous solution. 2Cl O2 + 2OH– Cl O2 – + Cl O3 – + H2O The initial rate of the reaction was measured at different initial concentrations of Cl O2 and OH–. The table shows the results obtained. experiment [Cl O2] / mol dm–3 [OH–] / mol dm–3 initial rate / mol dm–3 s–1 1.25 × 10–2 1.30 × 10–3 2.33 × 10–4 2.50 × 10–2 1.30 × 10–3 9.34 × 10–4 2.50 × 10–2 2.60 × 10–3 1.87 × 10–3 Use the data in the table to determine the rate equation, showing the order with respect to each reactant. Show your reasoning. rate equation = Calculate the value of the rate constant, k, using the data from experiment 2. State its units. k = units Explain the difference between heterogeneous and homogeneous catalysts. Complete the table using ticks () to indicate whether the catalyst used in the reaction is heterogeneous or homogeneous. catalysed reaction heterogeneous homogeneous manufacture of ammonia in the Haber process removal of nitrogen oxides from car exhausts oxidation of sulfur dioxide in the atmosphere Some reactions are catalysed by one of the products of the reaction. This is called autocatalysis. An example of autocatalysis is the reaction between acidifiedmanganate(ions, MnO4 –, and ethanedioicacid, (CO2H)2. Mn2+ ions catalyse this reaction. The reaction is slow in the absence of a catalyst. Balance the equation for this reaction. MnO4 – + H+ + (CO2H)2 Mn2+ + CO2 + H2O The graph shown is a concentration-time graph for a typical reaction. concentration of reactant time On the axes below, sketch the curve you would expect for the autocatalysed reaction in . concentration of MnO4 – time Describe, with the aid of a reaction pathway diagram, the effect of a catalyst on a reversible reaction. Suggest why catalysts are used in industrial processes. The reaction for the Haber process to produce ammonia is shown. N2+ 3H22NH3ΔH o = –92 kJ mol–1 At 500 °C, when pressure is measured in atmospheres, the numerical value of Kp for this equilibrium is 1.45 × 10–5. ● Write the expression for Kp for this equilibrium. Kp = ● Calculate the partial pressure of NH3 at equilibrium at 500 °C, when the partial pressure of N2 is 20atm and that of H2 is 60atm. pNH3 = atm
9701_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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The rate of chemical reactions is affected by changes in temperature and pressure. Draw a curve on the axes to show the Boltzmann distribution of energy of particles in a sample of gaseous krypton atoms at a given temperature. Label the curve T1 and label the axes.  On the diagram in , draw a second curve to show the distribution of energies of the krypton atoms at a higher temperature. Label the second curve T2. The Boltzmann distribution assumes that the particles behave as an ideal gas. State two assumptions of the kinetic theory as applied to an ideal gas.  2.00 g of krypton gas, Kr, is placed in a sealed 5.00 dm3 container at 120 °C. Calculate the pressure, in Pa, of Krin the container. Assume Krbehaves as an ideal gas. Show your working.  pressure = Pa State and explain the conditions at which krypton behaves most like an ideal gas. Krypton reacts with fluorine in the presence of ultraviolet light to make krypton difluoride, KrF2. Kr+ F2→ KrF2activation energy for the reaction, Ea = +385 kJ mol–1 enthalpy change of formation of KrF2, ∆Hf = +60.2 kJ mol–1 Use this information to complete the reaction profile diagram for the formation of KrF2. Label Ea and ∆Hf on the diagram. Assume the reaction proceeds in one step. energy / kJ mol–1 progress of reaction reactants  Explain, in terms of activation energy, Ea, and the collision of particles, how an increase in temperature affects the rate of a chemical reaction. 
9701_m21_qp_22
THEORY
2021
Paper 2, Variant 2
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Enzymes are a special group of protein molecules present in large amounts in living organisms. Enzymes behave as catalysts but, unlike inorganic catalysts, they generally catalyse only one particular reaction. Inorganic catalysts often work better on heating, but enzymes rarely work at temperatures much above 45°C. Explain why this is the case. Using the shape below to represent an enzyme, sketch how an enzyme is specific to the breakdown of a particular substrate molecule enzyme + substrate enzyme-substrate complex enzyme + products Describe the effects of a competitive, and of a non-competitive inhibitor on the interaction between enzyme and substrate. The diagram shown illustrates an enzyme-catalysed reaction. On the diagram sketch the graph that would be obtained if the same reaction was carried out in the presence of a non-competitive inhibitor. concentration of substrate / mol dm–3 initial reaction rate / mol dm–3 s–1 Explain why a non-competitive inhibitor has this effect on the reaction.
9701_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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Questions Discovered
220