8.1. Rate of reaction
A subsection of Chemistry, 9701, through 8. Reaction kinetics
Listing 10 of 86 questions
Ethanal, CH3CHO, dimerises in alkaline solution according to the following equation. 2CH3CHO → CH3CH(OH)CH2CHO The initial rate of this reaction was measured, starting with different concentrations of CH3CHO and OH–. The following results were obtained. / mol dm–3 [OH–] / mol dm–3 initial rate of reaction (relative values) 0.10 0.015 0.20 0.015 0.40 0.030 Deduce the order of the reaction with respect to CH3CHO. Deduce the order of the reaction with respect to OH–. State the overall rate equation for this reaction. rate = State the units for the rate constant, k. Calculate the initial rate of reaction (relative value) for a reaction where the is 0.30 mol dm–3 and [OH–] is 0.030 mol dm–3. A three-step mechanism has been proposed for the reaction in . step 1 CH3 C + + H O H2O C H O –CH2 –CH2 step 2 CH3 C + + + H O C H O CH3 CH2 C C H H O CH3 CH2 H2O C C H H O OH step 3 CH3 CH2 C C H H O –OH –OH –O –O Using your rate equation in , predict which is the rate-determining step. Explain your answer. rate-determining step explanation Describe the chemical behaviour of CH3CHO in step 1. Name the mechanism occurring in steps 2 and 3. Using the diagram below, show the mechanism for step 2 showing the relevant curly arrows and dipoles. –CH2 C H O CH3 C H O
9701_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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A student carries out four experiments to investigate the rate of reaction between 3.0g of calciumcarbonate and hydrochloric acid. CaCO3+ 2HCl→CaCl 2+ CO2+ H2O3 CaCO3 powder + 2.0moldm–3 HCl at 35°C experiment 1 CaCO3 powder + 2.0moldm–3 HCl at 35°C experiment 2 large chips of CaCO3 + 1.0moldm–3 HCl at room temperature experiment 3 large chips of CaCO3 + 1.0moldm–3 HCl at 35°C experiment 4 The student collects the CO2and times how long it takes to produce the same volume of gas for each experiment. What could be the correct times for the four experiments?
9701_m23_qp_12
MCQ
2023
Paper 1, Variant 2
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What do you understand by the term order of reaction? Cyanohydrins can be made by reacting ketones with an acidified solution of sodium cyanide. (CH3)2C=O + H+ + CN– →(CH3)2C(OH)CN In a series of experiments, the reaction was carried out with different concentrations of the three reagents, and the following relative initial rates were obtained. Use the data in the table to deduce the order of the reaction with respect to propanone hydrogen ions cyanide ions Hence write a rate equation for this reaction. Two different mechanisms have been suggested for this reaction Mechanism A: (CH3)2C=O + H+ → (CH3)2COH+ (CH3)2COH+ + CN– → (CH3)2C(OH)CN Mechanism B: (CH3)2C=O + CN– → (CH3)2C(O–)CN (CH3)2C(O–)CN + H+ → (CH3)2C(OH)CN Which mechanism is consistent with the rate equation you deduced in , and which step in this mechanism is the slower (rate determining) step? Explain your answer. Use experiment number [(CH3)2CO] / mol dm–3 [H+] / mol dm–3 [CN–] / mol dm–3 0.020 0.060 0.060 0.020 0.050 0.050 0.020 0.050 0.060 0.025 0.050 0.050 relative initial rate / mol dm–3sec–1 1.00 0.833 1.00 1.042
9701_s05_qp_4
THEORY
2005
Paper 4, Variant 0
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Phenacyl chloride has been used as a component of some tear gases. Its lachrymatory and irritant properties are due to it reacting with water inside body tissues to produce hydrochloric acid. It undergoes a nucleophilic substitution reaction with NaOH. O + OH– phenacyl chloride + Cl Write the formulae of the products of this reaction in the two boxes above. When the rate of this reaction was measured at various concentrations of the two reagents, the following results were obtained. experiment number [phenacyl chloride] relative rate 0.020 0.10 1.0 0.030 0.10 1.5 0.025 0.20 2.5 What is meant by the term order of reaction? Use the above data to deduce the order with respect to each reactant. Explain your reasoning. Write the overall rate equation for the reaction. Describe the mechanism for this reaction that is consistent with your overall rate equation. You should show all intermediates and/or transition states and partial charges, and you should represent the movements of electron pairs by curly arrows. Describe an experiment that would show that CH3COCl reacts with water at a much faster rate than phenacyl chloride. Include the reagents you would use, and the observations you would make with each chloride. Suggest an explanation for this difference in reactivity.
9701_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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Phenacyl chloride has been used as a component of some tear gases. Its lachrymatory and irritant properties are due to it reacting with water inside body tissues to produce hydrochloric acid. It undergoes a nucleophilic substitution reaction with NaOH. O + OH– phenacyl chloride + Cl Write the formulae of the products of this reaction in the two boxes above. When the rate of this reaction was measured at various concentrations of the two reagents, the following results were obtained. experiment number [phenacyl chloride] relative rate 0.020 0.10 1.0 0.030 0.10 1.5 0.025 0.20 2.5 What is meant by the term order of reaction? Use the above data to deduce the order with respect to each reactant. Explain your reasoning. Write the overall rate equation for the reaction. Describe the mechanism for this reaction that is consistent with your overall rate equation. You should show all intermediates and/or transition states and partial charges, and you should represent the movements of electron pairs by curly arrows. Describe an experiment that would show that CH3COCl reacts with water at a much faster rate than phenacyl chloride. Include the reagents you would use, and the observations you would make with each chloride. Suggest an explanation for this difference in reactivity.
9701_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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Questions Discovered
86