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Questions and Answers of Chemical Principles

A galvanic cell functions only when the electrical circuit is complete. In the external circuit the current is carried by the flow of electrons through a metal wire. Explain how the current is
A technical handbook contains tables of thermodynamic quantities for common reactions. If you want to know whether a certain cell reaction has a positive standard potential, which of the following
(a) If you were to construct a concentration cell in which one half-cell contains 1.0 m CrCl3(aq) and the other half-cell contains 0.0010 m CrCl3(aq), and both electrodes were chromium, at which
Dental amalgam, a solid solution of silver and tin in mercury, was used for filling tooth cavities. Two of the reduction halfreactions that the filling can undergo areSuggest a reason why, if you
Use the data in Appendix 2B and the fact that, for the half-reaction F2(g) + 2 H+(aq) + 2 e– → 2 HF(aq), E° = 13.03 V, to calculate the value of Ka for HF. 2B STANDARD POTENTIALS AT 25
Suppose that 25.0 mL of a solution of Ag+ ions of unknown concentration is titrated with 0.015 m KI(aq) at 25°C. A silver electrode is immersed in this solution, and its potential is measured
Suppose that 35.0 mL of 0.012 m Cu+(aq) is titrated with 0.010 m KBr(aq) at 25°C. A copper electrode is immersed in this solution, and its potential is measured relative to a standard hydrogen
The following items are obtained from a stockroom for the construction of a galvanic cell: two 250-mL beakers and a salt bridge, a voltmeter with attached wires and clips, 200 mL of 0.0080 m
(a) What is the standard cell potential (Ecell°) for the reaction below at 298 K?(b) What is the standard cell potential for the reaction at 335 K?(c) What is the cell potential for the reaction
(a) By considering the dependence of the Gibbs free energy of reaction on potential and on temperature, derive an equation for the temperature dependence of Ecell°.(b) Use your equation to predict
In a neuron (a nerve cell), the concentration of K+ ions inside the cell is about 20–30 times as great as that outside. What potential difference between the inside and the outside of the cell
(a) The potential of the cell Zn(s)|Zn2+(aq, ?)||Pb2+(aq, 0.10 mol · L–1)|Pb(s) is 10.661 V. What is the molar concentration of Zn2+ ions?(b) Write an equation showing how the Zn2+ ion
When a pH meter was calibrated with a boric acid–borate buffer with a pH of 9.40, the cell potential was +0.060 V. When the buffer was replaced with a solution of unknown hydronium ion
What is the standard potential for the reduction of oxygen to water in(a) An acidic solution and(b) A basic solution?(c) Is MnO4– more likely to be reduced to MnO4 2– in an acidic or a basic
What range (in volts) does a voltmeter need to have to measure pH in the range of 1 to 14 at 25°C if the voltage is zero when pH = 7?
The entropy change of a cell reaction can be determined from the change of the cell potential with temperature.(a) Show that ΔS° = nF(Ecell,2° – Ecell,1°)/(T2 – T1). Assume that ΔS° and
A silver concentration cell is constructed with the electrolyte at both electrodes being initially 0.10 m AgNO3(aq) at 25°C.The electrolyte at one electrode is diluted by a factor of 10 five times
Use only the data in Appendix 2B to calculate the acidity constant of HClO in water. 2B STANDARD POTENTIALS AT 25 °C Potentials in Electrochemical Order Reduction half-reaction Strongly
Consider the electroplating of a metal +1 cation from a solution of unknown concentration according to the half-reaction M+(aq) + e– → M(s), with a standard potential E°. When the half-cell is
An aqueous solution of Na2SO4 was electrolyzed for 30.0 min; 25.0 mL of oxygen was collected at the anode over water at 22°C and a total pressure of 722 Torr. Determine the current that was used to
The magnitudes of the standard potentials of two metals M and X were determined to beWhen the two electrodes are connected, current flows from M to X in the external circuit. When the electrode
A photoelectrochemical cell is an electrochemical cell that uses light to carry out an electrochemical reaction. The silicon electrodes in a photoelectrochemical cell being considered for the
The “aluminum–air fuel cell” is used as a reserve battery in remote locations. In this cell, aluminum reacts with the oxygen in air in basic solution.(a) Write the oxidation and reduction
What is(a) The electrolyte and(b) The oxidizing agent during discharge in a lead–acid battery?(c) Write the reaction that takes place at the cathode during the charging of the lead–acid
(a) Write the cell reaction for the lead–acid battery. (b) Explain how each of the following change in a lead–acid battery during discharge: pH; amount of PbO2; total amount of lead in the
What is(a) The electrolyte and(b) The oxidizing agent in the mercury cell shown here?(c) Write the overall cell reaction for a mercury cell. Steel cathode Zinc anode HgO in KOH and Zn(OH)₂
(a) Why are lead–antimony grids used as electrodes in the lead–acid battery rather than smooth plates?(b) What is the reducing agent in the lead–acid battery?(c) The lead–acid cell
Soluble nontoxic salts such as Fe2(SO4)3 are often used during water purification to remove soluble toxic contaminants, because they form gelatinous hydroxides that encapsulate the contaminants and
The body functions as a kind of fuel cell that uses oxygen from the air to oxidize glucose:During normal activity, a person uses the equivalent of about 10 MJ of energy a day. Assume that this value
A fuel cell in which hydrogen reacts with nitrogen instead of oxygen is proposed.(a) Write the chemical equation for the reaction in water, which produces aqueous ammonia.(b) What would be the
Suppose you need highly pure HI. You could prepare it by reacting hydrogen and iodine directly by the reaction H2(g) + I2(g) → 2 HI(g), provided that the reaction is sufficiently fast. You might
Many important biological reactions involve electron transfer. Because the pH of bodily fluids is close to 7, the “biological standard potential” of an electrode, E*, is measured at pH =
Complete the following statements relating to the production of ammonia by the Haber process, for which the overall reaction is N2(g) + 3 H2(g) →2 NH3(g). (a) The rate of consumption of N2 is
You are working for a manufacturer of cleaning supplies and are investigating the use of hydrogen peroxide, H2O2, as a stain removal agent in laundry detergent. However, the water available in the
The rate constant of the first-order reaction 2 N2O(g) → 2 N2(g) + O2(g) is 0.76 s–1 at 1000. K and 0.87 s–1 at 1030. K. Calculate the activation energy of the reaction.
The decomposition of ozone in the stratosphere is an issue of great concern because stratospheric ozone protects life on Earth. Suppose you are studying the mechanism of ozone decomposition. The
How does a catalyst affect(a) The rate of the reverse reaction;(b) The value of ΔHr° for the reaction?
In polar stratospheric clouds, nitrogen can be found as N2O5, which takes part in the ozone cycle that protects life on Earth. However, N2O5 decomposes over time. If you were studying the role of
Each of the following is an elementary reaction. Write its rate law and state its molecularity.(a) NO + NO → N2O2;(b) Cl2 → Cl + Cl.
An important reaction in organic chemistry is that of organic halides with hydroxide ion to form alcohols. You are interested in learning about the impact of temperature on the rate of this kind of
Beta blockers are drugs that are used to manage hypertension. It is important for doctors to know how rapidly a beta blocker is eliminated from the body. A certain beta blocker is eliminated in a
If you pursue a career in inorganic or physical chemistry, you may one day be studying the rate of the reaction of bromate ion with bromide ion. Suppose you conduct four experiments to discover how
The hydrolysis of sucrose is a part of the digestive process. Suppose you want to investigate how strongly the rate depends on body temperature and decide to calculate the rate constant for the
Complete the following statements for the reaction 6 Li(s) + N2(g) →2 Li3N(s). (a) The rate of consumption of N2 is ________________ times the rate of formation of Li3N. (b) The rate of formation
The rate constant of the second-order reaction 2 HI(g) → H2(g) + I2(g) is 2.4 * 10–6 L · mol–1 · s–1 at 575 K and 6.0 * 10–5 L · mol–1 · s–1 at 630. K. Calculate the activation
How does a homogeneous catalyst affect(a) The rate law;(b) The equilibrium constant of a reaction?
Many organic compounds can isomerize (turn into another compound with the same molecular formula) when heated. Suppose you are an organic chemist studying cyclopropane. You find that when
Each of the following is an elementary reaction. Write its rate law and state its molecularity.(a) OH + NO2 + N2 → HNO3 + N2 (N2 takes part in the collision, but is unchanged chemically);(b) ClO2
In the brewing of beer, ethanal, which smells like green apples, is an intermediate in the formation of ethanol. Ethanal decomposes in the following first-order reaction: CH3CHO(g) → CH4(g) +
Ethene is a component of natural gas, and its combustion has been thoroughly studied. At a certain temperature and pressure, the unique rate of the combustion reaction C2H4(g)+ 3 O2(g) →2 CO2(g) +
Volta discovered that when he used different metals in his “pile,” some combinations had a stronger effect than others. From that information he constructed an electrochemical series. How would
(a) Use a graphing calculator or standard graphing software to make an Arrhenius plot of the data shown here for the conversion of cyclopropane into propene and calculate the activation energy for
As in Example 7B.1, you are studying the decomposition of N2O5, but now you need to know how long it takes for a given amount of N2O5 to decompose. A sample of N2O5 is allowed to decompose by the
Write the overall reaction for the mechanism proposed below and identify any reaction intermediates. Step 1 AC + BAB+C Step 2 AC + AB →→→ A₂B + C
The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ · mol−1 to 75 kJ · mol−1.(a) By what factor does the rate of
Determine the rate constant for each of the following first-order reactions, in each case expressed for the rate of loss of A:(a) A → B, given that the concentration of A decreases to one-half its
(a) Use a graphing calculator or standard graphing software to make an Arrhenius plot of the data shown here for the decomposition of iodoethane into ethene and hydrogen iodide, C2H5I(g) → C2H4 (g)
The “iodine clock reaction” is a popular chemical demonstration. As part of that demonstration, the I3– ion is generated in the reaction S2O82– (aq) + 3 I–(aq) →2 SO4 2–(aq) +
Write the overall reaction for the mechanism proposed below and identify any reaction intermediates. + CH₂ + Br¯ Step 1 C,H,Br + Step 2 C₂H₂ + H₂O →C₂H₂OH₂+ Step 3 C₂H,OH₂++
In 1989, a teenager in Ohio was poisoned by breathing vapors from spilled mercury. The mercury level in his urine, which is proportional to its concentration in his body, was found to be 1.54 mg ·
The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 75 kJ · mol−1 to 52 kJ · mol−1.(a) By what factor does the rate of
Determine the rate constant for each of the following first-order reactions:(a) A → B + C, given that the concentration of A decreases to one-fourth its initial value in 125 min;(b) 2 A → D + E,
The decomposition of gaseous hydrogen iodide, 2 HI(g) → H2(g) 1 I2(g), gives the data shown here for 700. K.(a) Use a graphing calculator or standard graphing soft ware to plot the concentration of
The rate constant of the reaction between CO2 and OH– in aqueous solution to give the HCO3– ion is 1.5 * 1010 L · mol–1 · s–1 at 25°C. Determine the rate constant at human body temperature
The hydrolysis of an organic nitrile, a compound containing a—C≡N group, in basic solution, is proposed to proceed by the following mechanism. Write a complete balanced equation for the overall
The following mechanism has been proposed for the gasphase reaction between HBr and NO2:(a) Write the overall reaction. (b) Write the rate law for each step and indicate its molecularity. (c) What
Dinitrogen pentoxide, N2O5, decomposes by first-order kinetics with a rate constant of 3.7 * 10–5 s–1 at 298 K. (a) What is the half-life (in hours) of N2O5 at 298 K?(b) If [N2O5]0 = 0.0567 mol
Dinitrogen pentoxide, N2O5, decomposes by first-order kinetics with a rate constant of 0.15 s–1 at 353 K.(a) What is the half-life (in seconds) of N2O5 at 353 K?(b) If [N2O5]0 = 0.0567 mol ·
Consider the following mechanism for the hydrolysis of ethyl acetate. Write a complete balanced equation for the overall reaction, list any intermediates, and identify the catalyst in this reaction.
Ethane, C2H6, dissociates into methyl radicals at 700.°C with a rate constant kr = 5.5 * 10–4 s–1. Determine the rate constant at 870. °C, given that the activation energy of the reaction is
The decomposition of gaseous dinitrogen pentoxide in the reaction 2 N2O5(g) →4 NO2(g) + O2(g) gives the data shown here at 298 K. (a) Using a graphing calculator or standard graphing software,
A reaction was believed to occur by the following mechanism.(a) Write the overall reaction.(b) Write the rate law for each step and indicate its molecularity.(c) What are the reaction
Substance A decomposes in a first-order reaction and its half life is 355 s. How much time must elapse for the concentration of A to decrease to(a) One-eighth of its initial
For the reversible, one-step reaction A 1 A ⇄ B + C, the forward rate constant for the formation of B is 265 L · mol–1 · min–1 and the rate constant for the reverse reaction is 392 L ·
Decide which of the following statements about catalysts are true. If the statement is false, explain why.(a) In an equilibrium process, a catalyst increases the rate of the forward reaction but
Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for(a) Zeroth-order reactions;(b) First-order reactions;(c) Second-order reactions.
The following mechanism has been proposed for the reaction between nitric oxide and bromine:Write the rate law for the formation of NOBr implied by this mechanism. Step 1 NO Br₂ NOBr₂ Step 2
The first-order rate constant for the photodissociation of A is 1.24 * 10–3 min–1. Calculate the time needed for the concentration of A to decrease to(a) 25 % of its initial
For the reversible, one-step reaction A 1 B ⇄ C + D the forward rate constant is 52.4 L · mol–1 · h–1 and the rate constant for the reverse reaction is 32.1 L · mol–1 · h–1. The
Decide which of the following statements about catalysts are true. If the statement is false, explain why.(a) A heterogeneous catalyst works by binding one or more of the molecules undergoing
The mechanism proposed for the oxidation of iodide ion by the hypochlorite ion in aqueous solution is as follows:Write the rate law for the formation of HIO implied by this mechanism. Step 1 ClO +
Rate laws for gas-phase reactions can also be expressed in terms of partial pressures, for instance, as Rate 5 krPJ for a firstorder reaction of a gas J. What are the units for the rate constants
The Michaelis–Menten rate equation for enzyme reactions is typically written as the rate of formation of product (Eq. 1a).This equation implies that 1/rate (where rate is the rate of formation of
For the first-order reaction A → 3 B + C, when [A]0 = 0.015 mol · L–1, the concentration of B increases to 0.018 mol · L–1 in 3.0 min.(a) What is the rate constant for the reaction expressed
Three mechanisms for the reaction NO2(g) + CO(g) → CO2(g) + NO(g) have been proposed:Which mechanism agrees with the following rate law: Rate = kr[NO2]2? Explain your reasoning. Step 1 NO₂ + Step
Dinitrogen pentoxide, N2O5, decomposes by a first-order reaction. What is the initial rate of decomposition of N2O5 when 3.45 g of N2O5 is confined in a container of volume 0.750 L and heated to
Pyruvic acid is an intermediate in the fermentation of grains. During fermentation the enzyme pyruvate decarboxylase causes the pyruvate ion to release carbon dioxide. In one experiment, an aqueous
The following data were collected for the reaction 2 HI(g) → H2(g) + I2(g) at 580 K. (a) Use a graphing calculator or software to plot the data in an appropriate fashion to determine the order of
The Michaelis constant (KM) is an index of the stability of an enzyme–substrate complex. Does a high Michaelis constant indicate a long-lived or short-lived enzyme–substrate complex?Explain your
When the rate of the reaction 2 NO(g) + O2(g) → 2 NO2(g) was studied, the rate was found to double when the O2 concentration alone was doubled but to quadruple when the NO concentration alone was
Ethane, C2H6, dissociates into methyl radicals by a firstorder reaction at 700°C. If 820. mg of ethane is confined to a reaction vessel of volume 2.00 L and heated to 700°C, what is the initial
When 0.52 g of H2 and 0.19 g of I2 are confined to a reaction vessel of volume 750. mL and heated to 700. K, they react by a second-order process (first order in each reactant), with kr 5 0.063 L ·
The following data were collected for the reaction H2(g) + I2(g) → 2 HI(g) at 780 K. (a) Using a graphing calculator or software, plot the data in an appropriate fashion to determine the order of
Indicate whether each of the following statements is true or false. If a statement is false, explain why.(a) For a reaction with a very large equilibrium constant, the rate constant of the forward
When 510. mg of NO2 is confined to a reaction vessel of volume 180. mL and heated to 300°C, it decomposes by a second-order process. In the rate law for the decomposition of NO2, kr = 0.54 L ·
Indicate whether each of the following statements is true or false. If a statement is false, explain why.(a) The equilibrium constant for a reaction equals the rate constant for the forward reaction
The half-life of A in a second-order reaction is 50.5 s when [A]0 = 0.84 mol · L–1. Calculate the time needed for the concentration of A to decrease to (a) One-sixteenth; (b) One-fourth; (c)
In the reaction CH3Br(aq) + OH2(aq) → CH3OH(aq)+ Br2(aq), when the OH2 concentration alone was doubled, the rate doubled; when the CH3Br concentration alone was increased by a factor of 1.2, the
Consider the reaction A ⇄ B, which is first order in each direction with rate constants kr and kr′. Initially, only A is present. Show that the concentrations approach their equilibrium values at
Determine the rate constant for each of the following second-order reactions:(a) 2 A → B + 2 C, given that the concentration of A decreases from 2.50 mmol · L–1 to 1.25 mmol · L–1 in 100

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