Exam 6: Chemical Kinetics

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The mechanism for the gas-phase reaction that converts nitrogen dioxide, NO2, into nitric oxide, NO, and oxygen, O2 was explored by measuring the initial rate of the reaction for different pressures of reactant. The data below shows how the initial rate of reaction varied with the partial pressure of nitrogen dioxide at a temperature of 300 °C. An inert buffer gas was used so that the overall initial pressure was the same for each experiment. Use the method of initial rates to determine the order of the reaction. / 2000 4000 6000 8000 / 0.36 0.65 0.94 1.21

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The kinetics of the hydrolysis of methyl methanoate, CH3COOCH3, in aqueous solution were investigated by measuring the concentration of the ester after different time intervals. The reaction was found to be first order in the concentration of the ester. Use the data below to determine the rate constant for the reaction. time, 0 1800 3600 5400 7200 9000 t/ concentration, 0.300 0.191 0.135 0.081 0.055 0.035 c/ d

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For a large excess of oxygen, O2, the rate of production of nitrogen dioxide, NO2, by the gas-phase oxidation of nitric oxide, NO 2 NO(g) + O2 2 NO2(g) is found to be independent of the partial pressure of oxygen present. Under these conditions, the rate of formation of nitrogen dioxide was measured to be 8.34 10-13 s-1 for a concentration of nitric oxide of 5.38 10-6 mol dm-3. Use the description of the mechanism of the reaction given in section 11.5 to determine the rate constant for the dimerization of nitric oxide 2 NO(g) N2O2(g).

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For a solution-phase dimerization reaction, the rate constants for the second-order forward reaction is 2 107 dm3 mol-1 s-1 and for the first-order backward reaction is 4 105 s-1. Determine the equilibrium constant.

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The rate constant for the reaction 2 N2O(g) ? 2N2(g) + O2(g) Has been found to vary with temperature according to the following data. Determine the activation energy for the reaction. \theta/ 565 728 757 780 / 1.10\times1 0.380 0.871 1.67

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The rate constant for the reaction 2 N2O5(g) ⇌ 4 NO2(g) + O2(g) Is reported in units of s-1. What is the overall order of the reaction?

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For the isomerization of cyclopropane into propene Cyclo-C3H6 ∏ CH3CH=CH2 The rate constants of the forward and backward reactions are 1.47 1013 s-1 and 5.19 1012 s-1 respectively at a temperature of 1500 K. Determine the partial pressure of cyclopropane at equilibrium if the initial partial pressure is 0.100 bar.

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The transmittance of a sample is the ratio of the intensity of radiation transmitted to the intensity of the incident radiation. The molar absorption coefficient of the [Cu(NH3)4]2+ complex ion in aqueous solution is 50 dm3 mol-1 cm-1 at a wavelength of 590 nm. Determine the transmittance when light of this wavelength passes through an aqueous solution of the ion of molar concentration 0.100 mol dm-3 and path length 1.00 cm.

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The rate constant for the gas-phase reaction H2(g) + I2(g) 2 HI(g) Has the value 4.45 10-5 mol-1 dm3 s-1. What is the equivalent rate constant in units of molecule-1 cm3 s-1?

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The rate constant for the enzyme-catalysed decomposition of hydrogen peroxide, H2O2, increases by a factor of 3.8 when the temperature is increased from 298 K to 348 K. Determine the activation energy.

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Calculate the rate constant for the rate-determining step of a diffusion-controlled reaction that takes place in toluene, C6H5CH3, at 20 °C. The viscosity of toluene at this temperature is = 5.85 10-4 kg m-1 s-1.

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In an experiment to investigate the inhibition of the enzyme-glucosidase the following data for the rates of reaction with glucopyranoside for various substrate concentrations was obtained. By constructing a Leaver-Burk plot, determine the value of the Michaelis constant. [S]/ 1 1.00 2.00 3.00 4.00 V/ 1 16.7 33.3 41.1 49.8

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For the second-order reaction between methyl iodide, CH3I, and thiosulfate ions, S2O32-, ions in water, the Arrhenius pre-exponential factor is 2.19 1012 dm3 mol-1 s-1 and the activation energy is 78.7 kJ mol-1. Calculate the rate constant for the reaction at a temperature of 25°C.

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In a temperature-jump experiment to investigate the kinetics of protein folding, the relaxation time following perturbation of the equilibrated system was measured to be 240 ns. Both the forward and backward transformations were found to be first order, with the rate constant for the forward transformation known to be 1.1 106 s-1. Determine the rate constant for the backward transformation.

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Use collision theory to calculate an estimate of the Arrhenius pre-exponential factor for the reaction of two chlorine, 35Cl, atoms at a temperature of 298 K. The collisional cross section of a chlorine atom is estimated to be 0.064 nm2.

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Calculate the diffusion coefficient for the diffusion of a haemoglobin molecule through water at a temperature of 25°C. The effective cross sectional area of a haemoglobin macromolecule is 3.6 10-9 m2 and the viscosity of water is 8.90 10-4 kg m-1 s-1 at this temperature.

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The pyrolysis of ethane, C2H6 C2H6 C2H4 + H2 Proceeds through a multistep chain mechanism involving radicals, which are highly reactive species with one or more unpaired electrons. Radicals are formed in initiation steps, transferred in propagation steps and lost in termination steps. Retardation steps maintain the concentration of radical species but regenerate the reactant. One of the steps in the reaction mechanism is H + C2H6 H2 + C2H5 What is the best description of this step?

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The root-mean-square distance travelled by a molecule undergoing a one-dimensional random walk in a liquid or gas in a time interval is . The diffusion coefficient for the diffusion of sucrose through water at a temperature of 20°C is 4.59 10-10 m2 s-1. Calculate the distance through which a sucrose molecule moves in 1.00 ms.

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Analysis of the kinetics of the enzyme-catalysed hydrolysis of an ester by -chymotrypsin show that for an initial enzyme concentration of 4.5 10-9 mol dm-3, the maximum rate was 5.9 10-13 mol dm-3 s-1 and the Michaelis constant was 5.6 10-7 dm3 mol-1. Calculate the efficiency of the enzyme.

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The rate constant for the pseudo first-order acid-catalysed hydrolysis of glucose is 4.07 10-4 s-1. Calculate the half-life for the reaction.

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