Chem II: Chapter 21

Which of the following electrochemical reactions are spontaneous under standard conditions? Select all that apply.

2Co (s) + 3Cl2 (g) → 2CoCl3 (aq); Ecello = 1.6 V 2Cr (s) + 3Sn4+ (aq) → 2Cr3+ (aq) + 3Sn2+ (aq); Ecello = 0.89 V

If we were to solve for the cell potential of the following reaction, which two reactions would we first need to find in a standard reduction table? 2Ag+ (aq) + Zn (s) → 2Ag (s) + Zn2+ (aq)

Ag+(aq)+e--->Ag(s) Zn2+(aq)+2e--->Zn(s)

In an electrochemical cell, electrochemical reactions occur at the surface of two _________that are immersed in a(n) ________ solution.

Blank 1: electrodes Blank 2: electrolyte, ionic, or ion

By definition, if one coulomb of charge passes between two electrodes that differ in potential by one volt, one of energy is released. This relationship is correctly expressed as V = /. (Fill in units only, without values.)

Blank 1: joule or J Blank 2: joule or J Blank 3: C or coulomb

The measure of energy used in electrochemistry is the cell________ (Ecell), which is the difference in electrical potential between two electrodes. A common term for this difference in electrical potential is force or emf._______

Blank 1: potential or voltage Blank 2: electromotive

A(n) _________cell uses a spontaneous reaction to generate electrical energy. In this type of cell, the system does work on the_______ .

Blank 1: voltaic or galvanic Blank 2: surroundings

Which of the following is the proper shorthand notation for the redox reaction 2H+ (aq) + Cu (s) → Cu2+ (aq) + H2 (g)? (The hydrogen half-cell uses a graphite inactive electrode.) Multiple choice question.

Cu (s) | Cu2+ (aq) || H+ (aq) | H2 (g) | graphite

Match each cell potential with its implication for the spontaneity of the reaction.

Ecell > 0Reaction is spontaneous. Ecell < 0 Reaction is nonspontaneous. Ecell = 0 Reaction is at equilibrium.

Which of the following options correctly describe the units used to express electrical potential, charge, and electrical energy? Select all that apply.

Electrical energy can be measured in joules. the volt is the unit for electrical potential.

Which compounds or solutions are in an appropriate state for the measurement of Ecello for the reaction given below? Select all that apply. Cu2+ (aq) + H2 (g) → Cu (s) + 2H+ (aq)

H2 gas at 1 atm 1.0 M Cu2+

For the chemical reaction shown below, which of the following (unbalanced) reactions should be used as the starting point for the reduction half-reaction? 2Na + 2H2O → 2NaOH + H2

H2O → H2

Match each element with its most common oxidation number (assuming it is in a polar covalent or ionic bond).

Na: +1 F: -1 O: -2 Ca: +2

Given the following reaction, classify each species according to its ability to act as an oxidizing or reducing agent. Ni2+ (aq) + 2e- → Ni (s)

Ni2+: oxidizing Ni: reducing

Which of the following reactions result in the oxidation of sulfur? Select all that apply.

SO2 + H2O2 → H2SO4 S8 + 8O2 → 8SO2

Which of the following is required in order for an electrochemical reaction to generate an electric current? Multiple choice question.

The half-reactions must be physically separated.

When zinc metal is immersed in a 1.0 M solution of copper (II) chloride at 25oC, no electrochemical work may be extracted, even though a spontaneous reaction occurs. What is wrong with this cell design?

The oxidation and reduction reactions must be physically separated. Reason: The electrons transfer directly from Zn to Cu2+ in solution; no work may be extracted unless the two reactions are separated.

he electrode at which the oxidation reaction occurs is called the _____, while the electrode at which the reduction reaction occurs is called the _____.

anode; cathode

An electrochemical ________is the primary system for the study of electrochemical reactions.

cell

Oxidation involves the _____ of electrons, while reduction involves the _____ of electrons. Multiple choice question.

loss; gain

A species acts as a(n) _____ agent if it gains electrons in a half-reaction. Conversely, it could potentially act as a(n) _____ agent if it loses electrons in a half-reaction.

oxidizing; reducing

If a substance acts as a strong reducing agent, it will appear on a table of standard reduction potentials as the _____ in a half-reaction with a _____ standard reduction potential.

product; negative

If a substance acts as a strong oxidizing agent, it will appear on a table of standard reduction potentials as the _____ in a half-reaction with a _____ standard reduction potential.

reactant; positive

An electrochemical cell operates because the electrodes in the two half-cells differ in their electrical potential. A metal electrode composed of ______ reducing agent will have a greater electrical potential to push electrons toward the electrode composed of a ______ reducing agent. Multiple choice question.

stronger; weaker

Which of the following statements correctly describe standard electrode potentials? In what way must half-reactions and/or electrode potentials be manipulated when writing a balanced equation for a redox reaction?

By convention, standard electrode potentials are quoted as reduction potentials. The half-reaction for the anode must be reversed when writing the balanced equation for the overall reaction. Reason: Since standard half-reactions are generally written as reduction reactions, the reaction for the anode must be reversed when writing the balanced equation for the overall reaction.

Given the shorthand notation of an electrochemical cell shown below, match the component with the appropriate species. Ca (s) | Ca2+ (aq) || Pb2+ (aq) | Pb (s) Instructions

Ca (s) --->Reactant in anode compartment Ca2+ (aq) ---> Product in anode compartment Pb (s)---> Product in cathode compartment Pb2+ (aq)---> Reactant in cathode compartment

After spectator ions are eliminated, which of the listed species should be used when balancing the equation for the following redox reaction? Select all that apply. KMnO4 (aq) + Na2C2O4 (aq) + H2SO4 (aq) → MnSO4 (aq) + K2SO4 (aq) + Na2SO4 (aq) + CO2 (g)+ H2O (l)

MnO4- (aq) Mn2+ (aq) C2O42- H+ H2O (l) CO2

The reaction below is spontaneous in the forward direction. Which of the statements below provides the best reason for this observation? Ni (s) + 2Ag+ (aq) → Ni2+ (aq) + 2Ag (s)

Ni (s) gives its electrons away more freely than Ag (s).

The reaction below is spontaneous in the forward direction. Which of the statements below provides the best reason for this observation? Ni (s) + 2Ag+ (aq) → Ni2+ (aq) + 2Ag (s) Multiple choice question.

Ni (s) gives its electrons away more freely than Ag (s).

After spectator ions are eliminated, which of the listed species should be used when balancing the equation for the following redox reaction? Select all that apply. FeCl2 (aq) + NaOH (aq) + H2 (g) → Fe (s) + NaCl (aq) + H2O (l)

OH- (aq) Fe2+ (aq) H2O (l) H2 (g)

Based on the following reaction, identify ALL the species that should be included in the oxidation half-reaction equation. Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s) Multiple select question.

Zn (s) Zn2+ (aq)

In the diagram, electrons flow from the _____ electrode to the _____ electrode. Cations flow from the _____ cell to the _____ cell.

Zn; Cu; anode; cathode Reason: Na+ cations flow from the anode cell to the cathode cell.

n the diagram, electrons flow from the _____ electrode to the _____ electrode. Cations flow from the _____ cell to the _____ cell.

Zn; Cu; anode; cathode Reason: Na+ cations flow from the anode cell to the cathode cell.

The branch of chemistry that deals with the interconversion of electrical and chemical energy is called

electrochemistry

True or false: For a spontaneous redox reaction, the products are stronger oxidizing and reducing agents than the reactants. True false question.

false

If the oxidation number of a substance increases (becomes more positive), that substance has been)________ ; if the oxidation number decreases (becomes more negative), that substance has been__________ .

oxidized; reduced

If a substance causes another substance to be oxidized, that substance is a(n) _______agent. Likewise, the substance that is oxidized in an electrochemical reaction is always the _______ agent.

oxidizing; reducing

Match each symbol with the type of energy associated with it.

q - Heat V - Electrochemical Potential H - Enthalpy E - Internal Energy S - Entropy

The cell potential (Ecello) is measured with gases at a pressure of 1 atm, solutions at 1 M, and solids or liquids in their pure states.

standard

An electrochemical cell operates because the electrodes in the two half-cells differ in their electrical potential. A metal electrode composed of ______ reducing agent will have a greater electrical potential to push electrons toward the electrode composed of a ______ reducing agent.

stronger; weaker