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chemistry a molecular approach

Questions and Answers of Chemistry A Molecular Approach

The rate constant (k) for a reaction was measured as a function of temperature. A plot of ln k versus 1/T (in K) is linear and has a slope of -1.01 * 104 K. Calculate the activation energy for the
The tabulated data show the rate constant of a reaction measured at several different temperatures. Use an Arrhenius plot to determine the activation barrier and frequency factor for the reaction.
The tabulated data were collected for the second-order reaction:Cl(g) + H2(g) → HCl(g) + H(g)Use an Arrhenius plot to determine the activation barrier and frequency factor for the reaction.
The tabulated data show the rate constant of a reaction measured at several different temperatures. Use an Arrhenius plot to determine the activation barrier and frequency factor for the reaction.
A reaction has a rate constant of 0.000122/s at 27 °C and 0.228/s at 77 °C.a. Determine the activation barrier for the reaction.b. What is the value of the rate constant at 17 °C?
A reaction has a rate constant of 0.0117/s at 400.0 K and 0.689/s at 450.0 K.a. Determine the activation barrier for the reaction.b. What is the value of the rate constant at 425 K?
If a temperature increase from 10.0 °C to 20.0 °C doubles the rate constant for a reaction, what is the value of the activation barrier for the reaction?
Consider this overall reaction, which is experimentally observed to be second order in AB and zero order in C:Is the following mechanism valid for this reaction? AB + C A + BC
If a temperature increase from 20.0 °C to 35.0 °C triples the rate constant for a reaction, what is the value of the activation barrier for the reaction?
Which of these two reactions would you expect to have the smaller orientation factor? Explain. a. O(g) + N₂(8) NO(g) + N(g) b. NO(g) + Cl₂(g) → NOCI(g) + Cl(g)
Consider these two gas-phase reactions:a. AA(g) + BB(g) → 2 AB( g)b. AB(g) + CD(g) → AC(g) + BD(g)If the reactions have identical activation barriers and are carried out under the same
The proposed mechanism for the formation of hydrogen bromide can be written in a simplified form as:What rate law corresponds to this mechanism? Br₂(g) k₁ 2Br(g) Br(g) + H₂(g) H(g) +
A proposed mechanism for the formation of hydrogen iodide can be written in simplified form asWhat rate law corresponds to this mechanism? 1₂ k₁ I + H₂ H₂1 + I 21 k₂ k_₂ k3 H₂1 2
A certain substance X decomposes. Fifty percent of X remains after 100 minutes. How much X remains after 200 minutes if the reaction order with respect to X is (a) Zero order, (b) First order, (c)
The half-life for radioactive decay (a first-order process) of plutonium-239 is 24,000 years. How many years does it take for one mole of this radioactive material to decay until just one atom
The energy of activation for the decomposition of 2 mol of HI to H2 and I2 in the gas phase is 185 kJ. The heat of formation of HI(g) from H2( g) and I2( g) is -5.65 kJ/mol. Find the energy of
Ethyl chloride vapor decomposes by the first-order reaction:The activation energy is 249 kJ/mol, and the frequency factor is 1.6 * 1014 s-1. Find the value of the rate constant at 710 K.What fraction
The first-order integrated rate law for the reaction A → products is derived from the rate law using calculus:The equation just given is a first-order, separable differential equation that can be
In this chapter, we have seen a number of reactions in which a single reactant forms products. For example, consider the following first-order reaction:CH3NC(g) → CH3CN( g)However, we also learned
The previous exercise shows how the first-order integrated rate law is derived from the first-order differential rate law. Begin with the second-order differential rate law and derive the
The rate constant for the first-order decomposition of N2O5(g) to NO2(g) and O2(g) is 7.48 * 10-3 s-1 at a given temperature.a. Find the length of time required for the total pressure in a system
The rate of decomposition of N2O3(g) to NO2(g) and NO(g) is followed by measuring [NO2] at different times. The following data are obtained.The reaction follows a first-order rate law. Calculate the
At 473 K, for the elementary reaction2 NO(g) + Cl2(g)A sample of NOCl is placed in a container and heated to 473 K.When the system comes to equilibrium, [NOCl] is found to be 0.12 mol/L. What are the
Three different reactions involve a single reactant converting to products. Reaction A has a half-life that is independent of the initial concentration of the reactant, reaction B has a half-life
The accompanying graph shows the concentration of a reactant as a function of time for two different reactions. One of the reactions is first order, and the other is second order. Which of the two
A particular reaction, A → products, has a rate that slows down as the reaction proceeds. The half-life of the reaction is found to depend on the initial concentration of A. Determine whether each
A certain compound, A, reacts to form products according to the reaction A → P. The amount of A is measured as a function of time under a variety of different conditions, and the tabulated results
Methane (CH4) is a greenhouse gas emitted by industry, agriculture, and waste systems. Methane is the second most prevalent greenhouse gas (after carbon dioxide). Methane plays an important role in
A student says, “The initial concentration of a reactant was doubled, and the rate doubled. Therefore the reaction is second order in that reactant.” Why might the student say that? What is wrong
Consider the reaction:If a reaction mixture initially contains 0.110 M CO and 0.110 M H2O, what will the equilibrium concentration of each of the reactants and products be? CO(g) + H₂O(g) =
Find the pH of a 0.100 M HClO2 solution.
Rank the solutions in order of decreasing [H3O+]: 0.10 M HCl; 0.10 M HF; 0.10 M HClO; 0.10 M HC6H5O.
Without referring to the text, have each member of your group mention a different property of either an acid or a base, such as “Acids turn blue litmus paper red.” Record as many properties as
Calculate the pH of a buffer solution that is 0.100 M in HC2H3O2 and 0.100 M in NaC2H3O2.
A buffer is 0.100 M in NH4Cl and 0.100 M in NH3. When a small amount of hydrobromic acid is added to this buffer, which buffer component neutralizes the added acid? a) NH4+ b) Cl c) NH3 d) None of
Which solution is a buffer?(a) A solution that is 0.100 M in HNO2 and 0.100 M in HCl(b) A solution that is 0.100 M in HNO3 and 0.100 M in NaNO3(c) A solution that is 0.100 M in HNO2 and 0.100 M in
A buffer contains the weak acid HA and its conjugate base A–. The weak acid has a pKa of 4.82 and the buffer has a pH of 4.25.Which statement is true of the relative concentrations of the weak acid
What is the pH of a buffer that is 0.120 M in formic acid (HCHO2) and 0.080 M in potassium formate (KCHO2)? For formic acid, Ka = 1.8 * 10-4.a) 2.33 b) 3.57 c) 3.74 d) 3.91
A 1.0-L buffer solution contains 0.100 mol HC2H3O2 and 0.100 mol NaC2H3O2. The value of Ka for HC2H3O2 is 1.8 * 10-5. Because the initial amounts of acid and conjugate base are equal, the pH of the
A buffer with a pH of 9.85 contains CH3NH2 and CH3NH3Cl in water. What can you conclude about the relative concentrations of CH3NH2 and CH3NH3Cl in this buffer? For CH3NH2, pKb = 3.36. a) CH3NH₂ >
Use the Henderson–Hasselbalch equation to calculate the pH of a buffer solution that is 0.50 M in NH3 and 0.20 M in NH4Cl. For ammonia, pKb = 4.75.
A buffer contains equal amounts of a weak acid and its conjugate base and has a pH of 5.25. Which would be a reasonable value of buffer pH after the addition of a small amount of acid?(a) 4.15(b)
Which acid would you choose to combine with its sodium salt to make a solution buffered at pH 4.25? For the best choice, calculate the ratio of the conjugate base to the acid required to attain the
A 500.0-mL buffer solution is 0.10 M in benzoic acid and 0.10 M in sodium benzoate and has an initial pH of 4.19. What is the pH of the buffer upon addition of 0.010 mol of NaOH?a) 1.70b) 4.01 c)
Consider a buffer composed of the weak acid HA and its conjugate base A–. Which pair of concentrations results in the most effective buffer? a) 0.10 M HA; 0.10 M A c) 0.90 M HA; 0.10 M A b) 0.50 M
A 1.0-L buffer solution is 0.10 M in HF and 0.050 M in NaF. Which action destroys the buffer?(a) Adding 0.050 mol of HCl(b) Adding 0.050 mol of NaOH(c) Adding 0.050 mol of NaF(d) None of the above
The amount of strong acid in the flask shown here is to be titrated by a strong base. Which mark on the burette next to the flask indicates the amount of base required to reach the equivalence
A 50.0-mL sample of 0.200 M sodium hydroxide is titrated with 0.200 M nitric acid. Calculate pH:(a) After adding 30.00 mL of HNO3(b) At the equivalence point
Which combination is the best choice to prepare a buffer with a pH of 9.0? a) NH3; NH4Cl (pK, for NH3 is 4.75) b) C5H5N; C5H5NHCl (pK, for C5H5N is 8.76) c) HNO₂; NaNO₂ (pKa for HNO₂ is
Two 25.0-mL samples of unknown monoprotic weak acids, A and B, are titrated with 0.100 M NaOH solutions.The titration curve for each acid is shown below. Which of the two weak acid solutions is more
A 40.0-mL sample of 0.100 M HNO2 is titrated with 0.200 M KOH. Calculate:(a) The volume required to reach the equivalence point(b) The pH after adding 5.00 mL of KOH(c) The pH at one-half the
A 25.0-mL sample of an unknown HBr solution is titrated with 0.100 M NaOH. The equivalence point is reached upon the addition of 18.88 mL of the base. What is the concentration of the HBr solution?a)
Calculate the molar solubility of PbCl2 in pure water.
What is the pH at the half-equivalence point in the titration of a weak base with a strong acid? The pKb of the weak base is 8.75.(a) 8.75 (b) 7.0 (c) 5.25 (d) 4.37
A 10.0-mL sample of 0.200 M hydrocyanic acid (HCN) is titrated with 0.0998 M NaOH. What is the pH at the equivalence point? For hydrocyanic acid, pKa = 9.31.a) 7.00 b) 8.76 c) 9.31 d) 11.07
The molar solubility of Ag2SO4 in pure water is 1.4 * 10-2 M. Calculate Ksp.
Consider these three titrations:(i) The titration of 25.0 mL of a 0.100 M monoprotic weak acid with 0.100 M NaOH (ii) The titration of 25.0 mL of a 0.100 M diprotic weak acid with 0.100 M
A 20.0-mL sample of 0.150 M ethylamine is titrated with 0.0981 M HCl. What is the pH after the addition of 5.0 mL of HCl? For ethylamine, pKb = 3.25.a) 10.75 b) 11.04 c) 2.96 d) 11.46
What is the molar solubility of CaF2 in a solution containing 0.100 M NaF?
In which solution is BaSO4 most soluble?(a) A solution that is 0.10 M in BaNO3(b) A solution that is 0.10 M in Na2SO4(c) A solution that is 0.10 M in NaNO3
Three 15.0-mL acid samples—0.10 M HA, 0.10 M HB, and 0.10 M H2C—are all titrated with 0.100 M NaOH. If HA is a weak acid, HB is a strong acid, and H2C is a diprotic acid, which statement is true
A solution contains equal concentrations of Ba2+, Pb2+, and Ca2+ ions. When postassium sulfate is added to this solution, which cation precipitates first? (a) Ba²+ (b) Pb²+ (c) Ca²+
Determine whether each compound is more soluble in an acidic solution than it is in a neutral solution.(a) BaF2 (b) AgI (c) Ca(OH)2
A weak unknown monoprotic acid is titrated with a strong base.The titration curve is shown. Find Ka for the unknown acid. 14. 12. 10 Hd ∞0 60+ NO 8 a) 2.5 x 10-3 c) 3.2 x
A solution containing lead(II) nitrate is mixed with one containing sodium bromide to form a solution that is 0.0150 M in Pb(NO3)2 and 0.00350 M in NaBr. Does a precipitate form in the newly mixed
Which compound, when added to water, is most likely to increase the solubility of CuS?(a) NaCl (b) KNO3 (c) NaCN (d) MgBr2
Calculate the molar solubility of lead(II) bromide (PbBr2).For lead(II) bromide, Ksp = 4.67 * 10-6.a) 0.00153 Mb) 0.0105 Mc) 0.0167 Md) 0.0211 M
Calculate the molar solubility of magnesium fluoride (MgF2) in a solution that is 0.250 M in NaF. For magnesium fluoride, Ksp = 5.16 * 10-11. a) 2.35 x 10-4 M b) 2.06 x 10-10 M c) 2.87 x 10-5 M d)
The magnesium and calcium ions present in seawater ([Mg2+] = 0.059 M and [Ca2+] = 0.011 M) can be separated by selective precipitation with KOH. What minimum [OH-] triggers the precipitation of the
You add potassium hydroxide to the solution in Example 18.13. When the [OH-] reaches 1.9 * 10-6 M (as you just calculated), magnesium hydroxide begins to precipitate out of solution. As you continue
A solution is 0.0250 M in Pb2+. What minimum concentration of Cl– is required to begin to precipitate PbCl2?For PbCl2, Ksp = 1.17 * 10-5. a) 1.17 x 10-5 M b) 0.0108 M c) 0.0216 M d) 5.41 x 10-4 M
Which compound is more soluble in an acidic solution than in a neutral solution?a) PbBr2b) CuClc) AgId) BaF2
Consider this overall reaction, which is experimentally observed to be second order in X and first order in Y:a. Does the reaction occur in a single step in which X and Y collide?b. Is this two-step
Consider this three-step mechanism for a reaction:a. What is the overall reaction?b. Identify the intermediates in the mechanism.c. What is the predicted rate law? k₁ Cl₂(8) k₂ Cl(g) + CHCl3(8)
Consider this two-step mechanism for a reaction:a. What is the overall reaction?b. Identify the intermediates in the mechanism.c. What is the predicted rate law? NO₂(g) + Cl₂(8) NO₂(g) +
Many heterogeneous catalysts are deposited on high-surfacearea supports. Why?
Suppose that the reaction A¡products is exothermic and has an activation barrier of 75 kJ/mol. Sketch an energy diagram showing the energy of the reaction as a function of the progress of the
Suppose that a catalyst lowers the activation barrier of a reaction from 125 kJ/mol to 55 kJ/mol. By what factor would you expect the reaction rate to increase at 25 °C?
The tabulated data were collected for this reaction at 500 °C:a. Determine the order of the reaction and the value of the rate constant at this temperature.b. What is the half-life for this reaction
The activation barrier for the hydrolysis of sucrose into glucose and fructose is 108 kJ/mol. If an enzyme increases the rate of the hydrolysis reaction by a factor of 1 million, how much lower must
The tabulated data were collected for this reaction at a certain temperature:a. Determine the order of the reaction and the value of the rate constant at this temperature.b. What is the half-life for
Consider the reaction: A + B + C → DThe rate law for this reaction is:Suppose the rate of the reaction at certain initial concentrations of A, B, and C is 0.0115 M/s. What is the rate of the
At 700 K, acetaldehyde decomposes in the gas phase to methane and carbon monoxide. The reaction is: CH3CHO(g)¡CH4(g) + CO(g)A sample of CH3CHO is heated to 700 K, and the pressure is measured as
At 400 K, oxalic acid decomposes according to the reaction:H2C2O4(g) → CO2(g) + HCOOH(g)In three separate experiments, the initial pressure of oxalic acid and final total pressure after 20,000 s
Dinitrogen pentoxide decomposes in the gas phase to form nitrogen dioxide and oxygen gas. The reaction is first order in dinitrogen pentoxide and has a half-life of 2.81 h at 25 °C. If a 1.5-L
Cyclopropane (C3H6) reacts to form propene (C3H6) in the gas phase. The reaction is first order in cyclopropane and has a rate constant of 5.87 * 10-4/s at 485 °C. If a 2.5-L reaction vessel
Iodine atoms combine to form I2 in liquid hexane solvent with a rate constant of 1.5 * 1010 L/mol · s. The reaction is second order in I. Since the reaction occurs so quickly, the only way to study
The hydrolysis of sucrose (C12H22O11) into glucose and fructose in acidic water has a rate constant of 1.8 * 10-4 s-1 at 25 °C.Assuming the reaction is first order in sucrose, determine the mass of
The reaction AB(aq) → A( g) + B( g) is second order in AB and has a rate constant of 0.0118 M-1 · s-1 at 25.0 °C. A reaction vessel initially contains 250.0 mL of 0.100 M AB that is allowed to
The reaction 2 H2O2(aq) → 2 H2O(l) + O2( g) is first order in H2O2 and under certain conditions has a rate constant of 0.00752 s-1 at 20.0 °C. A reaction vessel initially contains 150.0 mL of
Consider this energy diagram:a. How many elementary steps are involved in this reaction?b. Label the reactants, products, and intermediates.c. Which step is rate limiting?d. Is the overall reaction
Consider the reaction in which HCl adds across the double bond of ethene:HCl + H2C = CH2→ H3C—CH2Cl The following mechanism, with the accompanying energy diagram, has been suggested for this
The desorption (leaving of the surface) of a single molecular layer of n-butane from a single crystal of aluminum oxide is found to be first order with a rate constant of 0.128/s at 150 K.a. What is
The kinetics of this reaction were studied as a function of temperature.a. Determine the activation energy and frequency factor for the reaction.b. Determine the rate constant at 15 °C.c. If a
The evaporation of a 120-nm film of n-pentane from a single crystal of aluminum oxide is zero order with a rate constant of 1.92 * 1013 molecules/cm2 · s at 120 K.a. If the initial surface coverage
The reaction 2 N2O5 → 2 N2O4 + O2 takes place at around room temperature in solvents such as CCl4. The rate constant at 293 K is found to be 2.35 * 10-4 s-1, and at 303 K the rate constant is
This reaction has an activation energy of zero in the gas phase:CH3 + CH3 →C2H6a. Would you expect the rate of this reaction to change very much with temperature?b. Why might the activation energy
Consider the two reactions:a. Why is the activation barrier for the first reaction so much higher than that for the second?b. The frequency factors for these two reactions are very close to each
Anthropologists can estimate the age of a bone or other sample of organic matter by its carbon-14 content. The carbon-14 in a living organism is constant until the organism dies, after which
Consider the gas-phase reaction:The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms.Proposed mechanism I:Proposed mechanism

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