8.1. Rate of reaction
A subsection of Chemistry, 9701, through 8. Reaction kinetics
Listing 10 of 86 questions
The compound nitrosyl bromide, NOBr, can be formed by the reaction shown. 2NO + Br2 2NOBr Using oxidation numbers, explain why this reaction is a redox reaction. Nitrosyl bromide contains a trivalent nitrogen atom. Draw the ‘dot-and-cross’ diagram for NOBr. Show outer electrons only. The rate of the reaction was measured at various concentrations of the two reactants, NO and Br2, and the following results were obtained. experiment / mol dm–3 / mol dm–3 initial rate / mol dm–3 s–1 0.03 0.02 3.4 × 10–3 0.03 0.04 6.8 × 10–3 0.09 0.04 6.1 × 10–2 0.12 0.06 to be calculated The general form of the rate equation for this reaction is as follows. rate = k ab What is meant by the term order of reaction with respect to a particular reagent? Use the data in the table to deduce the values of a and b in the rate equation. Show your reasoning. Use the data in the table to calculate the initial rate for experiment 4. initial rate = mol dm–3 s–1 Use the results of experiment1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = units By considering the rate equation, explain why the rate decreases with decreasing temperature. The reaction between X and Y was studied. 2X + Y Z The following sequence of steps is a proposed mechanism for the reaction. step 1 2X V step 2 V + Y Z The general form of the rate equation for this reaction is as follows. rate = k mn Step 1 is the slower step in the mechanism. Deduce the values of m and n in the rate equation. m = n =
9701_w17_qp_41
THEORY
2017
Paper 4, Variant 1
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The compound nitrosyl bromide, NOBr, can be formed by the reaction shown. 2NO + Br2 2NOBr Using oxidation numbers, explain why this reaction is a redox reaction. Nitrosyl bromide contains a trivalent nitrogen atom. Draw the ‘dot-and-cross’ diagram for NOBr. Show outer electrons only. The rate of the reaction was measured at various concentrations of the two reactants, NO and Br2, and the following results were obtained. experiment / mol dm–3 / mol dm–3 initial rate / mol dm–3 s–1 0.03 0.02 3.4 × 10–3 0.03 0.04 6.8 × 10–3 0.09 0.04 6.1 × 10–2 0.12 0.06 to be calculated The general form of the rate equation for this reaction is as follows. rate = k ab What is meant by the term order of reaction with respect to a particular reagent? Use the data in the table to deduce the values of a and b in the rate equation. Show your reasoning. Use the data in the table to calculate the initial rate for experiment 4. initial rate = mol dm–3 s–1 Use the results of experiment1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = units By considering the rate equation, explain why the rate decreases with decreasing temperature. The reaction between X and Y was studied. 2X + Y Z The following sequence of steps is a proposed mechanism for the reaction. step 1 2X V step 2 V + Y Z The general form of the rate equation for this reaction is as follows. rate = k mn Step 1 is the slower step in the mechanism. Deduce the values of m and n in the rate equation. m = n =
9701_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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Explain what is meant by the following terms. half-life of a reaction rate-determining step  The reaction between hydroxide ions and bromomethane is first order with respect to [OH–] and first order with respect to . CH3Br + OH– CH3OH + Br – Suggest a practical method that would confirm that the reaction is first order with respect to [OH–]. ● ● Your method should include details of measurements that would be taken in order to calculate the rate of the reaction. ● ● You should include a method of presenting the results to show that the reaction is first order with respect to [OH–]. The hydrolysis of methyl ethanoate, CH3CO2CH3, by hydroxide ions, OH–, is first order with respect to and also first order with respect to [OH–]. In a particular experiment, ● ●  = 0.100 mol dm–3 ● ● [OH–] = 0.100 mol dm–3 ● ● rate of reaction = 2.06 × 10–3 mol dm–3 s–1. Write a rate equation for this reaction and calculate the value of the rate constant, k, under these conditions. State the units of k. rate =  k = units =  
9701_w19_qp_42
THEORY
2019
Paper 4, Variant 2
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