GE-CHEM 1103 Module 4.3

Question 1

the study of the
relationships between electricity
and chemical reactions. It includes
the study of both spontaneous and
nonspontaneous processes.

Answer 1

Electrochemistry

Question 2

To keep track of what
loses electrons and
what gains them, we
assign

Answer 2

oxidation
numbers

Question 3

If the oxidation number
increases for an
element

Answer 3

element
is oxidized

Question 4

If the oxidation number
decreases for an
element

Answer 4

element
is reduced

Question 5

Synopsis of Assigning Oxidation Numbers

Answer 5

• Elements = 0
• Monatomic ion = charge
• F: –1
• O: –2 (unless peroxide = –1)
• H: +1 (unless a metal hydride = –1)
• The sum of the oxidation numbers equals
  the overall charge (0 in a compound).

Question 6

LEO

Answer 6

Loses Electron Oxidized

Question 7

GER

Answer 7

Gains Electron Reduced

Question 8

causes something else to be
oxidized

Answer 8

oxidizing agent

Question 9

causes something else
to be reduced

Answer 9

reducing agent

Question 10

• The oxidation and reduction are written
  and balanced separately.
• We will use them to balance a redox
  reaction.

Answer 10

Half-Reactions

Question 11

Balancing Redox Equations: The
Half-Reactions Method (For acidic solution)

Answer 11

1. Make two half-reactions (oxidation
   and reduction).
2. Balance atoms other than O and H.
   Then, balance O and H using H2O/H+.
3. Add electrons to balance charges.
4. Multiply by common factor
   to make electrons in half-reactions
   equal.
5. Add the half-reactions.
6. Simplify by dividing by common factor
   or converting H+
   to OH–
   if basic.
7. Double-check atoms and charges
   balance!

Question 12

Balancing in Basic Solution

Answer 12

• A reaction that occurs in basic solution can
  be balanced as if it occurred in acid.
• Once the equation is balanced, add OH–
  to
  each side to “neutralize” the H+
  in the
  equation and create water in its place.
• If this produces water on both sides,
  subtract water from each side so it appears
  on only one side of the equation.

Question 13

• In spontaneous redox
  reactions, electrons
  are transferred and
  energy is released.
• That energy can do
  work if the electrons
  flow through an
  external device.

Answer 13

Voltaic Cells

Question 14

oxidation occurs

Answer 14

anode

Question 15

reduction occurs

Answer 15

cathode

Question 16

When electrons flow, charges aren’t balanced so a contraption is used to keep the charges balanced

Answer 16

a salt bridge, usually a U-shaped tube that contains a salt/agar solution

Question 17

electrons leave
the anode and flow through
the wire to the cathode

Answer 17

cell

Question 18

formed in the
anode compartment

Answer 18

Cations

Question 19

electrons reach the
cathode

Answer 19

cations in solution
are attracted to the now
negative cathode

Question 20

gain electrons
and are deposited as metal
on the cathode

Answer 20

cations

Question 21

flow
spontaneously
one way in a
redox reaction,
from high to low
potential energy.

Answer 21

electrons

Question 22

potential difference between the anode
and cathode in a cell

Answer 22

electromotive force (emf)

Question 23

Other name of electromotive force (emf)

Answer 23

cell potential and is
designated Ecell

Question 24

It is measured in volts (V). One volt is one
joule per coulomb (1 V = 1 J/C).

Answer 24

cell potential

Question 25

Standard condition of a reduction potentials

Answer 25

1 M, 101.3 kPa, 25°C

Question 26

reference for the reduction potentials is called

Answer 26

standard hydrogen electrode (SHE)

Question 27

the reduction potential for hydrogen

Answer 27

0 V

Question 28

The cell potential at standard conditions can be found through this equation:

Answer 28

E°cell = E°red(cathode) - E°red(anode)

Question 29

cell potential is based on the potential energy per unit of charge

Answer 29

intensive property

Question 30

The more positive the value of E° red

Answer 30

the greater the tendency for reduction

Question 31

most positive reduction potentials

Answer 31

The strongest oxidizers

Question 32

most negative reduction potentials

Answer 32

The strongest reducers

Question 33

produce a positive cell potential, or emf.

Answer 33

Spontaneous redox reactions

Question 34

Equation for spontaneous redox reactions

Answer 34

E° = E° red (reduction) – E° red (oxidation)

Question 35

positive emf corresponds to negative ΔG

Answer 35

Since Gibbs free energy is the measure of spontaneity

Question 36

How is Free Energy, Redox, and K related

Answer 36

ΔG° = –nFE° = –RT ln K

Question 37

Nernst equation

Answer 37

E = E° – (RT/nF) ln Q OR E = E° – (2.303 RT/nF) log Q

Question 38

Nernst equation (Using standard thermodynamic temperature and the constants R and F)

Answer 38

E = E° – (0.0592/n) log Q

Question 39

a cell could be created that has the same substance at both electrodes

Answer 39

concentration cell

Question 40

as long as the concentrations are different

Answer 40

E will not be 0

Question 41

Some Applications of Cells

Answer 41

– Batteries – Prevention of corrosion – Electrolysis

Question 42

Examples of batteries

Answer 42

* Lead–acid battery * Alkaline battery * Ni–Cd and Ni–metal hydride batteries * Lithium-ion batteries

Question 43

reactants and products are solids, so Q is 1 and the potential is independent of concentrations; however, made with lead and sulfuric acid (hazards)

Answer 43

* Lead–acid battery

Question 44

most common primary battery

Answer 44

* Alkaline battery

Question 45

lightweight, rechargeable; Cd is toxic and heavy, so hydrides are replacing it

Answer 45

* Ni–Cd and Ni–metal hydride batteries

Question 46

rechargeable, light; produce more voltage than Ni-based batteries

Answer 46

* Lithium-ion batteries

Question 47

the energy created can be converted to electrical energy

Answer 47

fuel is burned ( this conversion is only 40% efficient, with the remainder lost as heat)

Question 48

The direct conversion of chemical to electrical energy is expected to be more efficient and is the basis for it

Answer 48

fuel cells

Question 49

are NOT batteries; the source of energy must be continuously provided

Answer 49

fuel cells

Question 50

* In this cell, hydrogen and oxygen form water. * The cells are twice as efficient as combustion. * The cells use hydrogen gas as the fuel and oxygen from the air.

Answer 50

Hydrogen Fuel Cells

Question 51

it is an oxidation and its common name is rusting

Answer 51

Corrosion

Question 52

occurs because zinc is more easily oxidized, so that metal is sacrificed to keep the iron from rusting

Answer 52

Cathodic protection

Question 53

A method to prevent corrosion is used for underground pipes wherein the anode is oxidized before the pipe

Answer 53

sacrificial anode

Question 54

Use of electrical energy to create chemical reactions

Answer 54

electrolysis

Question 55

1 coulomb

Answer 55

1 ampere × 1 second

Question 56

equation for Q (relation to electrolysis and stoichiometry)

Answer 56

= It = nF

Question 57

Q represents

Answer 57

charge (C)

Question 58

I represents

Answer 58

current (A)

Question 59

t represents

Answer 59

time (s)

Question 60

n represents

Answer 60

moles of electrons that travel through the wire in the given time NOTE: n is different than that for the Nernst equation!

Question 61

F represents

Answer 61

= Faraday’s constant (96,485 C/mol)