8.1. Rate of reaction
A subsection of Chemistry, 9701, through 8. Reaction kinetics
Listing 10 of 86 questions
What is meant by the term ligand as applied to the chemistry of the transition elements? Describe the type of bonding that occurs between a ligand and a transition element. Chromium hexacarbonyl undergoes the following ligand replacement reaction. Cr(CO)6 + PR3 Cr(CO)5PR3 + CO Two separate experiments were carried out to study the rate of this reaction. In the first experiment, the ligand PR3 was in a large excess and [Cr(CO)6] was measured with time. The results are shown on the graph below. 0.00000 0.00200 0.00400 0.00600 concentration / mol dm–3 0.00800 0.01000 time/s In the second experiment, Cr(CO)6 was in a large excess, and was measured with time. The following results were obtained. time / s / mol dm–3 0.0100 0.0076 0.0060 0.0028 Plot the data in the table on the graph above, using the same axis scales, and draw the best-fit line through your points. Use the graphs to determine the order of reaction with respect to Cr(CO)6 and PR3. In each case explain how you arrived at your answer. Cr(CO)6 PR3 Write the rate equation for the reaction, and calculate a value for the rate constant, using the method of initial rates, or any other method you prefer. State the units of the rate constant. Four possible mechanisms for this reaction are given below. Draw a circle around the letter next to the one mechanism which is consistent with the rate equation you have written in . A Cr(CO)6 Cr(CO)5 + CO fast Cr(CO)5 + PR3 Cr(CO)5PR3 slow B Cr(CO)6 Cr(CO)5 + CO slow Cr(CO)5 + PR3 Cr(CO)5PR3 fast C Cr(CO)6 + PR3 [OC- - -Cr(CO)4- - -PR3] Cr(CO)5PR3 + CO (transition state) D Cr(CO)6 + PR3 Cr(CO)6PR3 slow Cr(CO)6PR3 Cr(CO)5PR3 + CO fast Explain your answer.
9701_w11_qp_43
THEORY
2011
Paper 4, Variant 3
View
Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other substances known as inhibitors. State one example of a substance that can act as a non-competitive inhibitor in enzyme reactions. For the inhibitor you have identifi ed, explain why it is a non-competitive inhibitor. The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor. rate of reaction concentration of substrate On the same axes, sketch a graph showing the rate of this reaction if a competitive inhibitor was present. DNA is responsible for encoding the amino acid sequence to produce proteins. Ribosome, tRNA and mRNA are all involved in the process of protein synthesis. Write ribosome, tRNA and mRNA in the boxes below to show the correct sequence in which they are involved. DNA protein Sequences of three bases code for specifi c amino acids. The code UGA however does not usually code for an amino acid. Suggest its use. Much of the energy used in biochemical reactions is provided by the hydrolysis of the molecule ATP. What are the breakdown products of the hydrolysis of ATP? Give two uses for the energy released by ATP hydrolysis in cells. 1. 2.
9701_w13_qp_43
THEORY
2013
Paper 4, Variant 3
View
The oxidation of nitrogen(oxide is shown in the equation. 2NO+ O2→ 2NO2The initial rate of this reaction was measured, starting with different concentrations of the two reactants. The following results were obtained. experiment number / mol dm–3 / mol dm–3 initial rate / mol dm–3 s–1 0.032 0.012 4.08 × 10–3 0.032 0.024 8.15 × 10–3 0.064 0.024 3.28 × 10–2 0.096 0.036 Use the data in the table to determine the order with respect to each reactant. Show your reasoning. Calculate the initial rate in experiment 4. Give your answer to two signifi cant fi gures. initial rate = mol dm–3 s–1 Write the rate equation for this reaction. Use the results of experiment 1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = units On the following axes ● draw two Boltzmann distribution curves, at two different temperatures, T1 and T2 (T2 > T1), ● label the curves and the axes. State and explain, using your diagram, the effect of increasing temperature on the rate of reaction. The compound nitrosyl fl uoride, NOF, can be formed by the following reaction. 2NO+ F22NOFThe rate is fi rst order with respect to NO and F2. The reaction mechanism has two steps. Suggest equations for the two steps of this mechanism, stating which is the rate determining slower step.
9701_w14_qp_41
THEORY
2014
Paper 4, Variant 1
View
The oxidation of nitrogen(oxide is shown in the equation. 2NO+ O2→ 2NO2The initial rate of this reaction was measured, starting with different concentrations of the two reactants. The following results were obtained. experiment number / mol dm–3 / mol dm–3 initial rate / mol dm–3 s–1 0.032 0.012 4.08 × 10–3 0.032 0.024 8.15 × 10–3 0.064 0.024 3.28 × 10–2 0.096 0.036 Use the data in the table to determine the order with respect to each reactant. Show your reasoning. Calculate the initial rate in experiment 4. Give your answer to two signifi cant fi gures. initial rate = mol dm–3 s–1 Write the rate equation for this reaction. Use the results of experiment 1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = units On the following axes ● draw two Boltzmann distribution curves, at two different temperatures, T1 and T2 (T2 > T1), ● label the curves and the axes. State and explain, using your diagram, the effect of increasing temperature on the rate of reaction. The compound nitrosyl fl uoride, NOF, can be formed by the following reaction. 2NO+ F22NOFThe rate is fi rst order with respect to NO and F2. The reaction mechanism has two steps. Suggest equations for the two steps of this mechanism, stating which is the rate determining slower step.
9701_w14_qp_42
THEORY
2014
Paper 4, Variant 2
View
Bromate(ions, BrO3 –, react with bromide ions in the presence of acid to produce bromine. Write an ionic equation for this reaction. The initial rate of this reaction was measured, starting with different concentrations of the three reactants. The following results were obtained. experiment number [BrO3 –] / mol dm–3 [Br –] / mol dm–3 [H+] / mol dm–3 initial rate / mol dm–3 s–1 0.040 0.020 0.50 2.64 × 10–4 0.040 0.020 1.00 1.06 × 10–3 0.040 0.080 0.50 1.06 × 10–3 0.080 0.020 0.50 5.21 × 10–4 Use the data in the table to determine the order with respect to each reactant. Show your reasoning. Write the rate equation for this reaction. Use the results of experiment 1 to calculate the rate constant, k, for this reaction. Include the units of k. rate constant, k = units
9701_w14_qp_43
THEORY
2014
Paper 4, Variant 3
View
In aqueous solution, 2-chloro-2-methylpropane, (CH3)3CCl, reacts with sodium hydroxide, NaOH. This is a nucleophilic substitution reaction. (CH3)3CCl + NaOH→ (CH3)3COH+ NaCl Show the mechanism for this reaction. Include all necessary curly arrows, lone pairs and relevant dipoles. The rate of this reaction was investigated using a large excess of sodium hydroxide. The graph below shows the results of the experiment. 0.60 0.50 0.40 0.30 0.20 0.10 time / s [(CH3)3CCl ] / mol dm–3 The reaction is first order with respect to [(CH3)3CCl ]. This can be confirmed from the graph using half-lives. What is meant by the half-life of a reaction? Calculate the half-life for this reaction. Show all your working and show clearly any construction lines on the graph. What would be the effect on the half-life of this reaction if the initial concentration of [(CH3)3CCl ] was doubled? Use the graph in to determine the rate of reaction at 80 s. Show all your working. rate = units The rate equation for this reaction is shown. rate = k [(CH3)3CCl ] Calculate the value of the rate constant, k, for this reaction and give its units. k = units
9701_w15_qp_41
THEORY
2015
Paper 4, Variant 1
View
In aqueous solution, 2-chloro-2-methylpropane, (CH3)3CCl, reacts with sodium hydroxide, NaOH. This is a nucleophilic substitution reaction. (CH3)3CCl + NaOH→ (CH3)3COH+ NaCl Show the mechanism for this reaction. Include all necessary curly arrows, lone pairs and relevant dipoles. The rate of this reaction was investigated using a large excess of sodium hydroxide. The graph below shows the results of the experiment. 0.60 0.50 0.40 0.30 0.20 0.10 time / s [(CH3)3CCl ] / mol dm–3 The reaction is first order with respect to [(CH3)3CCl ]. This can be confirmed from the graph using half-lives. What is meant by the half-life of a reaction? Calculate the half-life for this reaction. Show all your working and show clearly any construction lines on the graph. What would be the effect on the half-life of this reaction if the initial concentration of [(CH3)3CCl ] was doubled? Use the graph in to determine the rate of reaction at 80 s. Show all your working. rate = units The rate equation for this reaction is shown. rate = k [(CH3)3CCl ] Calculate the value of the rate constant, k, for this reaction and give its units. k = units
9701_w15_qp_42
THEORY
2015
Paper 4, Variant 2
View
Questions Discovered
86