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Flashcards in Chapter 13 Deck (22)
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1

Redox Reaction

 

Involves transer of electrons from one species to another.

Fe3+   +    V2+ → Fe2+  +  V3+

                                               Oxidizing        Reducing

                                                            agent              agent

2

Oxidized

 

Species is oxidized when it loses electrons

3

Reduced

 

Species is reduced when it gains electrons

4

Oxidant

 

  • 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+

 

5

Reductant

 

  • 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+

6

Electric Charge (q)

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

7

Faraday Constant (F)

 

1 mole of electrons has a charge of:

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

8

Relationship between charge and moles

 

q = n • F

where:

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

9

Current

 

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

10

Pt electrode

 

  • 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)

11

Electric Potential (E)

 

  • 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.

12

Work

 

Work = E • q

Where:

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

13

Free Energy Change (ΔG)

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

14

Ohm's Law

 

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

15

Power (P)

 

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

16

Galvanic Cell

 

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

17

Half-Reaction

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

18

Cathode

The electrode at which reduction occurs

19

Anode

 

The electrode at which oxidation occurs

20

Standard Reduction Potential Eº

 

  • 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.

21

Standard Hydrogen Electrode (S.H.E.)

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

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

S.H.E. at 25ºC = 0 V

22

Formal Potential (Eº' )

 

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

  • pH
  • Ionic Strength
  • Concentration of complexing agents