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Problem 113c,d
Platinum nanoparticles of diameter 2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of 3.924 Å. (c) Using your results from (a) and (b), calculate the percentage of Pt atoms that are on the surface of a 2.0-nm nanoparticle. (d) Repeat these calculations for a 5.0-nm platinum nanoparticle.
Problem 114
One of the many remarkable enzymes in the human body is carbonic anhydrase, which catalyzes the interconversion of carbon dioxide and water with bicarbonate ion and protons. If it were not for this enzyme, the body could not rid itself rapidly enough of the CO2 accumulated by cell metabolism. The enzyme catalyzes the dehydration (release to air) of up to 107 CO2 molecules per second. Which components of this description correspond to the terms enzyme, substrate, and turnover number?
- Suppose that, in the absence of a catalyst, a certain biochemical reaction occurs x times per second at normal body temperature 37 °C. In order to be physiologically useful, the reaction needs to occur 5000 times faster than when it is uncatalyzed. By how many kJ/mol must an enzyme lower the activation energy of the reaction to make it useful?
Problem 115
Problem 116a
Enzymes are often described as following the two-step mechanism:
E + S ⇌ ES (fast)
ES → E + P (slow)
where E = enzyme, S = substrate, ES = enzyme9substrate complex, and P = product.
(a) If an enzyme follows this mechanism, what rate law is expected for the reaction?
Problem 116b
Enzymes are often described as following the two-step mechanism:
E + S ⇌ ES (fast)
ES → E + P (slow)
where E = enzyme, S = substrate, ES = enzyme9substrate complex, and P = product.
(b) Molecules that can bind to the active site of an enzyme but are not converted into product are called enzyme inhibitors. Write an additional elementary step to add into the preceding mechanism to account for the reaction of E with I, an inhibitor.
- Dinitrogen pentoxide (N2O5) decomposes in chloroform as a solvent to yield NO2 and O2. The decomposition is first order with a rate constant at 45 _x001E_C of 1.0 * 10^-5 s^-1. Calculate the partial pressure of O2 produced from 1.00 L of 0.600 M N2O5 solution at 45 _x001E_C over a period of 20.0 h if the gas is collected in a 10.0-L container. (Assume that the products do not dissolve in chloroform.)
Problem 117
- The reaction between ethyl iodide and hydroxide ion in ethanol solution, C2H5I(alc) + OH-(alc) → C2H5OH(l) + I-(alc), has an activation energy of 86.8 kJ/mol and a frequency factor of 2.10 × 10^11 M^-1 s^-1. (b) A solution of KOH in ethanol is made up by dissolving 0.335 g KOH in ethanol to form 250.0 mL of solution. Similarly, 1.453 g of C2H5I is dissolved in ethanol to form 250.0 mL of solution. Equal volumes of the two solutions are mixed. Assuming the reaction is first order in each reactant, what is the initial rate at 35 _x001E_C?
Problem 118
Problem 118c
The reaction between ethyl iodide and hydroxide ion in ethanol (C2H5OH) solution, C2H5I(alc) + OH-(alc) → C2H5OH(l) + I-(alc), has an activation energy of 86.8 kJ/mol and a frequency factor of 2.10 × 1011 M-1 s-1. (c) Which reagent in the reaction is limiting, assuming the reaction proceeds to completion?
Problem 118d
The reaction between ethyl iodide and hydroxide ion in ethanol (C2H5OH) solution, C2H5I(alc) + OH-(alc) → C2H5OH(l) + I-(alc), has an activation energy of 86.8 kJ/mol and a frequency factor of 2.10 × 1011 M-1 s-1. (d) Assuming the frequency factor and activation energy do not change as a function of temperature, calculate the rate constant for the reaction at 50 C.
Problem 120b
The gas-phase reaction of NO with F2 to form NOF and F has an activation energy of Ea = 6.3 kJ/mol. and a frequency factor of A = 6.0 × 108 M-1 s-1. The reaction is believed to be bimolecular: NO(g) + F2(g) → NOF(g) + F(g) (b) Draw the Lewis structures for the NO and the NOF molecules, given that the chemical formula for NOF is misleading because the nitrogen atom is actually the central atom in the molecule.
Problem 120e
The gas-phase reaction of NO with F2 to form NOF and F has an activation energy of Ea = 6.3 kJ>mol. and a frequency factor of A = 6.0 * 108 M-1 s-1. The reaction is believed to be bimolecular: NO1g2 + F21g2 ¡ NOF1g2 + F1g2 (e) Suggest a reason for the low activation energy for the reaction.
Problem 121a
The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (a) Calculate the overall standard enthalpy change for the reaction process.
Problem 121c
The mechanism for the oxidation of HBr by O2 to form 2 H2O and Br2 is shown in Exercise 14.74. (c) Draw a plausible Lewis structure for the intermediate HOOBr. To what familiar compound of hydrogen and oxygen does it appear similar?
- The rates of many atmospheric reactions are accelerated by the absorption of light by one of the reactants. For example, consider the reaction between methane and chlorine to produce methyl chloride and hydrogen chloride: Reaction 1: CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g). This reaction is very slow in the absence of light. However, Cl2(g) can absorb light to form Cl atoms: Reaction 2: Cl2(g) + hv → 2 Cl(g). Once the Cl atoms are generated, they can catalyze the reaction of CH4 and Cl2, according to the following proposed mechanism: Reaction 3: CH4(g) + Cl(g) → CH3(g) + HCl(g). Reaction 4: CH3(g) + Cl2(g) → CH3Cl(g) + Cl(g). The enthalpy changes and activation energies for these two reactions are tabulated as follows: Reaction ΔH (kJ/mol) Ea (kJ/mol); 3: +4, 17; 4: -109, 4. (c) By using bond enthalpies, estimate where the reactants, CH4(g) + Cl2(g), should be placed on your diagram in part (b). Use this result to estimate the value of Ea for the reaction CH4(g) + Cl2(g) → CH3(g) + HCl(g) + Cl(g).
Problem 122
Problem 122b
The rates of many atmospheric reactions are accelerated by the absorption of light by one of the reactants. For example, consider the reaction between methane and chlorine to produce methyl chloride and hydrogen chloride:
Reaction 1: CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g)
This reaction is very slow in the absence of light. However, Cl2(g) can absorb light to form Cl atoms:
Reaction 2: Cl2(g) + hv → 2 Cl(g)
Once the Cl atoms are generated, they can catalyze the reaction of CH4 and Cl2, according to the following proposed mechanism:
Reaction 3: CH4(g) + Cl(g) → CH3(g) + HCl(g)
Reaction 4: CH3(g) + Cl2(g) → CH3Cl(g) + Cl(g)
The enthalpy changes and activation energies for these two reactions are tabulated as follows:
Reaction ΔH° (kJ/mol) Ea (kJ/mol)
3 +4 17
4 -109 4
(b) By using the data tabulated here, sketch a quantitative energy profile for the catalyzed reaction represented by reactions 3 and 4.
- Many primary amines, RNH2, where R is a carbon-containing fragment such as CH3, CH3CH2, and so on, undergo reactions where the transition state is tetrahedral. (b) What kind of reactant with a primary amine can produce a tetrahedral intermediate?
Problem 123
Problem 123a
Many primary amines, RNH2, where R is a carboncontaining fragment such as CH3, CH3CH2, and so on, undergo reactions where the transition state is tetrahedral. (a) Draw a hybrid orbital picture to visualize the bonding at the nitrogen in a primary amine (just use a C atom for 'R').
- The NOx waste stream from automobile exhaust includes species such as NO and NO2. Catalysts that convert these species to N2 are desirable to reduce air pollution. (b) Using a resource such as Table 8.3, look up the energies of the bonds in these molecules. In what region of the electromagnetic spectrum do these energies lie?
Problem 124
- The NOx waste stream from automobile exhaust includes species such as NO and NO2. Catalysts that convert these species to N2 are desirable to reduce air pollution. Design a spectroscopic experiment to monitor the conversion of NOx into N2, describing what wavelengths of light need to be monitored as a function of time.
Problem 124