Chapter 13

Question 1

Redox Reaction

Answer 1

Involves transer of electrons from one species to another.

Fe³⁺ + V²⁺ → Fe²⁺ + V³⁺

                                           Oxidizing        Reducing

                                                        agent              agent

Question 2

Oxidized

Answer 2

Species is oxidized when it loses electrons

Question 3

Reduced

Answer 3

Species is reduced when it gains electrons

Question 4

Oxidant

Answer 4

• aka: Oxidizing Agent
• takes electrons from another substance and becomes reduced
• Fe³⁺ + V²⁺ → Fe²⁺ + V³⁺*
• Fe³⁺ is the because it takes an electron from V²⁺

Question 5

Reductant

Answer 5

• aka reducing agent
• gives electrons to another substance and is oxidized

Fe³⁺ + V²⁺ → Fe²⁺ + V³⁺

• V²⁺ is the reducing agent because it gives an electron to Fe³⁺

Question 6

Electric Charge (q)

Answer 6

• Measured in coulombs (C)
• Magnitude of the charge of a single electron is 6.02 • 10^-19 C
  *

Question 7

Faraday Constant (F)

Answer 7

1 mole of electrons has a charge of:

(1.602 • 10^-19)(6.022 • 10²³ mol^-1) = 96485 C

Question 8

Relationship between charge and moles

Answer 8

q = n • F

where:

• q is in coulombs
• n is number of moles of electrons transferred
• F is Faraday’s constant

Question 9

Current

Answer 9

• Quantity of charge flowing each second through a circuit
• Unit: Ampere (A)
• 1 amp = 1 ^C/_s

Question 10

Pt electrode

Answer 10

• conducts electrons into or out of a chemical species in the redox reaction.
• Inert electrode - does not participate in the redox chemistry (except as a conductor of electrons)

Question 11

Electric Potential (E)

Answer 11

• The difference between two points is the work needed (or that can be done) when moving an electric charge from one point to the other.
• Units: Volts (V)
• Note: 1 V = 1 ^J/_C
• The greater the potential difference between two points, the stronger the “push” on a charged particle [moving between the points] will be.

Question 12

Work

Answer 12

Work = E • q

Where:

• Work is in Joules
• E is in Volts
• q is in Coulombs

Question 13

Free Energy Change (ΔG)

Answer 13

The free energy change (ΔG) for a chemical reaction conducted reversibly at constant temperature and pressue euqls the maximum possible electrical work that can be done by the reaction on its surroundings:

ΔG = - work = - E • q

ΔG = -nFE

Question 14

Ohm’s Law

Answer 14

States that current is directly proportional to the potential difference across a circuit and inversely proportional to the resistance of the circuit.

I = ^E/_R

Units of resistance: ohms (Ω)

Note: ampere is equivalent to ^V/_Ω

Question 15

Power (P)

Answer 15

• The work done per unit time.
• P = E • I
• Units: Watt (W)
• W = ^J/_s

Question 16

Galvanic Cell

Answer 16

• aka Voltaic Cell
• Uses a spontaneous chemical rxn to generate electricity

Question 17

Half-Reaction

Answer 17

The net reaction is composed of a reduction and an oxidation, each of which is a half-reaction.

Question 18

Cathode

Answer 18

The electrode at which reduction occurs

Question 19

Anode

Answer 19

The electrode at which oxidation occurs

Question 20

Standard Reduction Potential E^º

Answer 20

• The tendency for a chemical species to be reduced
• Measured in volts at standard conditions.
• The more positive the potential is the more likely it will be reduced.
• Electrons always flow toward more positive potential.

Question 21

Standard Hydrogen Electrode (S.H.E.)

Answer 21

Consists of a catalytic Pt surface in contact with an acidic solution in which A_H⁺ = 1

S.H.E. half-rxn: H⁺(aq, A=1) + e^- ⇔¹/₂H₂ (g, A=1)

S.H.E. at 25ºC = 0 V

Question 22

Formal Potential (Eº’ )

Answer 22

The reduction potential that applies under a specified set of conditions, including:

• pH
• Ionic Strength
• Concentration of complexing agents