In a spectrophotometric experiment, 84.9% of the incident light is absorbed by the solution under investigation. If the solution is of concentration 0.069 mol dm–3, and the path length of the cell is 12.5 mm, calculate the molar absorption coefficient of the solution.
Which of the following would be correct units for the rate constant of a reaction that is second order overall?
The rate constant for the reaction
H2 + OH® H + H2O
which is an important step in the hydrogen–oxygen reaction mechanism, has the value kr = 3.52 ´ 106 mol–1 dm3 s–1. What is the equivalent value expressed in units of molecule–1 cm3 s–1?
Which of the following statements about the kinetics of the reaction
H2(g) + Br2(g) ® 2HBr (g) is definitely true?
In an experiment to investigate the mechanism of the condensation reaction between acrolein and 1,3-butadiene, the initial rate was measured spectrophotometrically for various different partial pressures of the reactants. The table below shows the initial rates of reaction, v0, for various partial pressures of acrolein, p, at a temperature of 560 K with 1,3-butadiene being in excess.
p / Pa
1260
3310
4930
6610
v0 / (1012 Pa s–1) 3.88
9.32
14.40
10.86
Use the method of initial rates to determine the order of the reaction with respect to acrolein.
In an investigation of the first-order decomposition reaction
C2H5I ® C2H4 + HI
at a temperature of 400K, the partial pressure of C2H5I, p, was found to vary with time, t, as shown below. Determine the rate constant of the reaction.
p / Torr
74.0
57.1
44.0
34.0
26.2
t / s
0
10.0
20.0
30.0
40.0
The half life for the acid-catalysed hydrolysis of sucrose to form glucose and fructose, which is first order overall, is 3.20 h at 25 °C. What is the rate constant for the reaction at this temperature?
The rate constant for the second order reaction between iodomethane, CH3I, and ethoxy anions, C2H5O–, in ethanol solution is 9.86 ´ 10–5 mol dm–3 s–1 at 298 K and 6.17 ´ 10–3 mol dm–3 s–1 at 338 K. Calculate the activation energy.
The rate constant for the substitution reaction
C4H9Cl + H2O ® C4H9OH + HCl
increases by a factor of 10.6 when the temperature is increased from 298 K to 308 K. Calculate the activation energy of the reaction.
Predict the Arrhenius pre-exponential factor for the reaction
H2 + CO ® H2CO
at 298.15 K, given that the collision cross section of H2 is 0.0452 nm2 and of CO is 0.0804 nm2.
For the recombination of two methyl, CH3, radicals
2 CH3 ® C2H6
the rate constants for the forward and backward reactions have been measured to be kf = 2.58 ´ 1013 mol–1 cm3 s–1 and kb = 5.36 ´ 10–4 s–1 respectively at a temperature of 1000 K. Calculate the equilibrium constant at this temperature. Remember that for a gas-phase reaction such as this, it will be necessary to express the concentrations in terms of the partial pressures of the various species.
The hydrolysis of t-bromobutane, C4H9Br, by hydroxide, OH–, ions in aqueous solution follows an SN1 reaction mechanism in which the rate-determining step is the loss of a bromide, Br–, ion, followed by rapid reaction with hydroxide ions. Which of the following rate laws is consistent with this mechanism?
The rate law for the multistep chain reaction
H2 + Br2 ® 2 HBr
is
Which of the following expresses the rate law in the limit of high pressures of bromine, Br2?
The thermal decomposition of acetone, (CH3)2CO, proceeds via the formation of the stable intermediate ketene, CH2CO
(CH3)2CO ® CH2CO + CH4
CH2CO ® ½C2H4 + CO
The rate constant for the initial decomposition of acetone is ka = 5.25 ´ 10–3 s–1, whilst the rate constant for the subsequent decomposition of ketene is kb = 15.23 ´ 10–3 s–1, at a temperature of 600 °C. Calculate the time after which the ketene intermediate has reached its maximum concentration.
The isomerisation of cis- to trans-but-2-ene, C4H8, follows a Lindemann mechanism. At high pressure, the pseudo first-order rate constant for the isomerisation is 2 ´ 10–5 s–1 at 500 °C. Given that, at this temperature, collisional activation occurs with an efficiency that is 1011 times slower than that of collisional deactivation, determine the rate constant for the final step of the mechanism.
The concentration gradient of ferrocene molecules in an aqueous ethanol solution in an electrochemical cell at 25 °C is 1.2 mmol dm–3 cm–1. Calculate the magnitude of the flux of ferrocene molecules towards the electrode, given that the coefficient for diffusion of ferrocene in a dilute aqueous ethanol solution is 6.0 ´ 10–10 m2 s–1.
The root-mean-square distance travelled by a molecule in a liquid or gas in a time interval t is
The diffusion coefficient for a dextrose molecule in water is D = 0.673 ´ 10–9 m2 s–1 at a temperature of 298.15 K. How far does an individual dextrose molecule travel in 1.00 s?
The diffusion coefficient for diffusion of collagen through water at 20°C has been measured to be 0.069 ´ 10–10 m2 s–1. Use the Einstein relation to calculate the effective radius of a collagen molecule, given that the viscosity of water at this temperature is 8.9 ´ 10–4 kg m–1 s–1.
The kinetics of many radical–radical recombination reactions are diffusion controlled. Calculate the rate constant for a diffusion-controlled bimolecular reaction in water at 77 °C. The viscosity of water at this temperature is h = 6.90 ´ 10–4 kg m–1 s–1.
The table below shows how, for the myosin-catalysed hydrolysis of ATP, the rate of reaction varies with substrate concentration.
v / (10–6 mol dm–3 s–1) 0.067
0.095
0.119
0.149
[S] / (10–5 mol dm–3) 7.5
12.5
32.5
By constructing a Lineweaver–Burk plot, determine the value of the Michaelis constant.
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