Electrochemistry Flashcards

1
Q

Define electrochemistry

A

the interconversion of chemical and electrical energy
- spontaneous reactions can produce electricity and electricity can cause non-spontaneous reactions to occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

redox reactions involve

A

the movement of electrons from one reagent to another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

oxidation

A

loss of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

reduction

A

gain of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

oxidising agent

A
  • reduced
  • takes electrons from the substance being oxidised
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

reducing agent

A
  • oxidised
  • gives electrons away
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how to balance redox reactions

A
  • write down the two half-reactions
  • balance the atoms and charges in each half-reaction
  • first balance atoms other than O and H, then O, then H
  • charge is b balanced by adding electrons (e-) to the reactant side of the reduction half-reaction and to the product side in the oxidation half-reaction
  • electrons should cancel out in net reaction. if necessary, multiply one or both half-reactions by an integer so that number of e- gained in reduction = number of electrons lost in oxidation
  • add the balanced half-reactions and include states of matter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

two types of electrochemical cells

A
  • voltaic cells
  • electrolytic cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

voltaic/galvanic cells

A

spontaneous chemical reaction (ΔG<0) generates an electric current
- batteries contain one or more voltaic cells
- voltaic cell does work on the surroundings, converting higher energy reactants in the cell into lower energy products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

electrolytic cells

A

non-spontaneous reactions (ΔG>0) are driven by electric current
- external power source supplies free energy to run electrolytic cells. the surroundings thus do work on the cell. lower energy reactants are converted to higher energy products in the cell
- used for electroplating, purification of metals, and more

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

electric current is

A

flow of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

electrons only flow if

A

the driving force (free energy change) is large enough

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

electrodes

A

usually metal strips/wires connected by an electrically conducting wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

anode

A

electrode where oxidation takes place

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

cathode

A

electrode where reduction takes place

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

describe salt bridge

A

U-shaped tube that contains a gel permeated with a solution of inert electrolyte (contains positive and negative spectator ions).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

function of salt bridge

A

The salt bridge keeps half cells electrically neutral because ions flow in and out of the salt bridge, counteracting charge build-up due to electron flow.

18
Q

conventions for notation for a voltaic cells

A
  • anode components are written on the left
  • cathode components are written on the right
  • components of each half cell are written in the same order as in their half reactions
  • single line shows a phase boundary between the components of a half cell
  • double line shows that the half cells are physically separated
19
Q

addition notation for voltaic cell that is more complex

A

any inactive (inert) electrode is specified
a comma is used to show components that are in the same phase

20
Q

why does a voltaic cell work?

A
  • differing abilities of metals to gain electrons gives rise to a voltage drop
  • this is also known as electromotive force (EMF) or cell potential
21
Q

multimeter

A

can measure voltage

22
Q

cell potential (Ecell)

A

the difference in electrical potential between two electrodes

23
Q

units for Ecell

A

measured in Volts (V), where

V = J/C (Colomb is SI unit of charge)

24
Q

difference in Ecell for voltaic and electrolytic cells

A

Voltaic: Ecell>0 (spontaneous e- flow)
electrolytic: Ecell<0 (non-spontaneous e-flow)

25
when Ecell = 0,
the redox reaction has reached equilibrium so the cell can do no more work
26
define standard potential (E'cell)
cell potential under standard state conditions
27
how to calculate Ecell from Ehalf-cell
the cell potential of any electrochemical cell is the sum of the half cell potentials for the oxidation and reduction half cells Ecell = E ox + E red
28
what does it mean to say that E is an intensive property?
Bigger cells with more moles of redox components will last longer, but will have the same standard output voltage
29
which half cell will form the oxidation half cell?
the lower Ered (ie more negative/less positive = worse at being reduced)
30
use of standard hydrogen electrode
- potentials are determined experimentally from the difference in potential between two electrodes - the reference point is called the standard hydrogen electrode
31
Standard Hydrogen Electrode
consists of a platinum electrode in contact with H2 gas (1atm) and aqueous H+ ions (1M)
32
standard hydrogen electrode is assigned (arbitrarily) a value of
exactly 0.00 V
33
how is Ecelll related to ΔG?
ΔG = -nFE(cell) = -RTln(Keq) - ΔG is in J/mol - n is in mol and is the no of moles of electrons transferred per mole of the reaction - F is faraday's constant
34
at equilibrium, ΔG = and Ecell =
0
35
Nernst Equation
E = E' - RT/nF (lnQ) E = E' - 0.0592V/n logQ E - The cell potential (electromotive force, EMF) under non-standard conditions, measured in volts (V). The standard cell potential, which is the voltage of the electrochemical cell under standard conditions
36
how does cell potential depend on the relative concentration of reactants and products?
when Q<1, lnQ<0 so Ecell>E'cell when Q=1, lnQ=0 so Ecell = E' cell when Q>1, lnQ>1 so Ecell
37
two consequences of cell potential depending on the relative concentration of reactants and products:
- as a cell is operated, concentration of reactants will decrease and products will increase. thus, cell potential will decrease over time - concentration cells - capture the electrical energy from a concentration difference
38
how is a concentration cell created
- has the same half-reaction in both cell compartments, but with different concentrations of electrolyte - there is a potential difference between cells, which drives current flow until both compartments have an equal concentration of ions - Ecell>0 as long as the half-cell concentrations are different - once the concentrations equalise, Ecell = 0 and current stops flowing
39
write equations for corrosion
40
how to protect against corrosion
Galvanisation: coating of iron with zinc. Zinc is more easily oxidised than iron, giving up electrons to it. Iron is more easily reduced than zinc.