BCHEM 163 Exam 4 2023 with 100% correct questions and answers

Which of A-D is a disadvantage in using hydrogen fuel cells instead of gasoline engines in vehicles? If all are valid disadvantages, respond E. a. No distribution network of hydrogen fuel is in place b. It is difficult to store hydrogen safely c. Hydrogen fuel is not really a source of energy, but rather is a way to store energy d. Hydrogen fuel must be produced, most likely from water, by using another source of energy e. All of the above E The numerical Value of the faraday constant is approximately 96,500. This value represents ____ a. the number of electrons required to produce one mole of electrical charge b. the number of electrons required to produce a charge of one coulomb c. the number of ions produced by removing one mole of electrons d. the electrical current produced by transferring one mole of electrons. e. the coulombs of charge carried by one mole of electrons E Which one of the following items does not characterize and oxidizing agent? a. an oxidizing agent gains electrons. b. an oxidizing agen causes another species to be oxidized c. a good oxidizing agent is a metal in a high oxidation states such as Mn⁷⁺ d. An example of a good oxidizing agent is an alkali metal, such as Na e. The oxidation number of an oxidizing agent decreases. D What is the oxidation number of chromium in the ionic compound ammonium dichromate, (NH₄)₂Cr₂O₇? a. +6 d. +4 b. +7 e. +3 c. +5 A An electrochemical cell is represented below. Which statement about this cell is not correct? Cu(s)|Cu²⁺(aq)(0.20 M)‖Ag⁺(aq)(0.10 M)|Ag(s) a. silver ion is reduced b. electrons flow from the copper to the silver electrode c. the cell potential is determined by the standard half-cell potentials alone. d. Two moles of electrons are transferred in the balanced reaction equation. e. Copper is oxidized C Does the pH have an effect on the cell potential (E cell) for the following oxidation-reduction reactions 5Fe²⁺(aq)+MnO₄⁻(aq)+8H⁺(aq)→5Fe³⁺(aq)+Mn²⁺(aq)+4H₂O(l) a. yes, because Ecell values for redox reactions involving the hydronium ion depend on the pH b. No, because Ecell values for redox reactions depend only on the major species in the reaction, in this case, Fe²⁺, MnO₄⁻, Fe³⁺, and Mn²⁺ c. yes, because Ecell calues for all redox reactions depend of the pH d. No, because Ecell values for redox reactions do not depend of the pH e. no, because Ecell values for redox reactions depend on concentrations and temperatures but not on pH. A The spontaneous redox reaction in a voltaic cell has _____ a. a positive value of Ecell and a positive value of ∆G b. a negative value of Ecell and a positive value of ∆G c. a negative value of Ecell and a negative value of ∆G d. a positive value of Ecell and a value of zero of ∆G e. a positive value of Ecell and a negative value of ∆G E The Nernst equation can be used to calculate _____ a. cell potentials given the temperature and reactant concentrations b. standard cell potentials from standard reduction potentials c. cell potentials from standard oxidation potentials d. cell potentials from standard cell potentials when the conditions of concentration and temperature are not standard e. the change n standard Gibbs free energy from standard cell potentials D If the potential of a voltaic cell is +1.20V, what is the free-energy change when one mole of electrons is transferred in the oxidation-reduction reaction? a. 116kj d. +602kj b. 1.20 kj e. -116kj c. -1.20 kj E The init of current, ampere (A) is defined as ______ a. 1 mol of electrons b. 1 mol of electrons per second c. 96, 500 C/s d. 1 C/s e. 1 C D When a voltaic cell reaches equilibrium, ________ a. Ecell=0 b. E°cell=0 c. E°cell=K d. Ecell=Q e. Ecell-K A Which statement about a voltaic cell is not correct? a. reduction occurs at the cathode b. Chemical species can have their oxidation number decrease at the cathode c. In the external circuit, electrons flow towards the cathode. d. Usually the cathode is a metal strip e. electrons are produced as a product at the cathode. E Glancing at a periodic table, where do you expect to find elements that are good oxidizing agents? a. at the bottom b. in the transition metals c. on the right (except at for the last group) d. in the middle left e. in the top left C In the smelting of iron from iron oxide according to the equation Fe₂O₃(s)+3CO(g)→2Fe(s)_3CO₂(g) What is the change in oxidation number for iron? a. +3 b. 0 c. -3 d. +2 e. -2 C The standard hydrogen electrode is _________ a. often overlooked in measuring standard reduction potentials b. used to calibrate voltmeters c. used to produce a set of standard reduction potentials d. used to produce a standard cell potential of exactly 1V e. needed to activate electrochemical cells C Which statement is not correct for a voltaic cell? a. electrons are transferred from the oxidizing agent to the reducing agent b. the electron flow in the external circuit is from the negative electrode to the positive electrode c. the electron flow in the external circuit is from the anode to the cathode d. positive ions diffuse through a porous bridge from the anode compartment to the cathode compartment e. chemical energy is transformed into electrical energy by a spontaneous redox reaction. A Which statement regarding voltaic cells is not correct? a. reduction occurs at the cathose b. electrons flow in the external circuit toward the electrode represented by a positive sign. c. electron flow in the external circuit from the cathode to the anode d. the electrode where reduction is occurring is represented by a positive sign e. anions move through the barrier or bridge toward the electrode where oxidation is occurring. C Condsider the coltaic cell based on the following reaction: Ma(s)+Mb⁺(a)→Ma⁺(aq)+Mb(s) Two students are assigned to measure the standard cell potential. Yvone claims that both solutions of ions have to be exactly 1.00M concentration, but zelda is sure that the measurement will be the same if the concentrations of the two solutions are equal, but not necessarily 1.00M. What to you think? a. Both are right because cell potentials do not depend of concentrations b. Zelda is right because cell potentials do not depend on concentrations c. Yvonne is right because by definition standard cell potentials must be measured at concentrations of 1.00M d. Yvonne is right because she understands the Nernst equation and what it describes e. Zelda is right because she understands the Nernst equation and what it describes e Applying a current to a rechargeable battery converts it from ______ cell to ______cell. a. a Born cell, a Haver b. a Nernst; a Leclanche c. an electrolytic, a voltaic d. a Leclanche; a Nernst e. a Voltaic; an electrolytic E The oxidation of hydrogen by oxygen is one of the most-used reactions in fuel-cell technology. The overall reaction, which is given below, has a ∆G° value of -237 kj/mol. What is the standard cell potential for this fuel cell? H₂(g)+½O₂(g)→H₂O(l) a. 3.05 V b. 4.91 V c. 1.23 V d. 2.46 V e. 1.50 V C Which one of the following items foes not characterize a reducing agent? a. a good reducing agent is a metal in a high oxidation stat, such as Mn⁷⁺ b. a reducing agen loses electrons c. The oxidation number of a reducing agent increases d. A reducing agent causes another species to be reduced e. An example of a good reducing agent is an alkali metal, such as Na A What is true when a battery (voltaic cell) is dead? a. Ecell=0 and Q=0 b. E°cell=0 and Q=K c. Ecell=0 and Q=K d. Ecell=0 and K=0 e. E°cell=0 and Q=0 C An electrochemical cell with a standard hydrogen electrode and a cathose consisting of a metallic chromium electrode, Cr(s), in contact with a 1.00 M chromium solution, Cr³⁺(aq), was constructed. The coltage produced by this cell was measured at 25°C. Which statements describe the result of this measurement, assuming the conditions are idea? I. The cell potential II. The electomotive force III. the standard cell potential IV. The standard reduction potential for Cr/Cr³⁺ a. I, II, and III d. I, II, III, and IV b. I only e. I and II c. III only D