Electrochemistry

For an atom in its element form (such as Na, O2, and Cl2): oxidation number = WHAT

For an atom in its element form (such as Na, O2, and Cl2): oxidation number = ZERO

For a monatomic ion: Oxidation number = WHAT

For a monatomic ion: Oxidation number = ION CHARGE (with the sign before the numeral)

The sum of the oxidation number values for the atoms in a molecule or formula unit of a compound equals WHAT. The sum of the oxidation number values for the atoms in a polyatomic ion equals the WHAT of the WHAT 

The sum of the oxidation number values for the atoms in a molecule or formula unit of a compound equals ZERO. The sum of the oxidation number values for the atoms in a polyatomic ion equals the CHARGE of the ION  

Oxidation number for group 1 

Oxidation number = +1 in all compounds 

Oxidation number for group 2

Oxidation number = +2 in all compounds 

Oxidation number for hydrogen

Oxidation number = + 1 in combinations with nonmetals

Oxidation number = -1 in combination with metals and boron 

Oxidation number for fluorine

Oxidation number = -1 in all compounds

Oxidation number for oxygen

Oxidation number = -2 in most cases, unless coupled to a more electronegative center (such as F) or a group 1 or group 2 metal (in which case, it may be +2 or -1) 

Oxidation number for group 17

Oxidation number = -1 in combination with metals, nonmetals (except o) and other halogens lower in the group 

The oxidizing agent takes electrons from the substance being WHAT

• Species being WHAT 

The oxidizing agent takes electrons from the substance being OXIDIZED

• Species being REDUCED 

The reducing agent gives electrons to the substance being WHAT 

• Species being WHAT 

The reducing agent gives electrons to the substance being REDUCED 

• Species being OXIDIZED 

What are the two types of cells

• Galvanic/Voltaic cell 

• Electrolytic cell 

Electrode: Part of the cell to make WHAT connection and allow WHAT flow

• Active electrodes - WHAT 

• Passive electrodes - WHAT 

Electrode: Part of the cell to make ELECTRICAL connection and allow ELECTRON flow

• Active electrodes - Electrode that IS part of the redox RXN  

• Passive electrodes - Electrode that IS NOT part of the redox RXN (eg, Pt, Hg, C(s)) 

Anode 

• Where WHAT occurs 

• Electrons flow WHERE 

• WHAT ion flow toward 

Anode 

• Where OXIDATION occurs 

• Electrons flow AWAY from the anode  

• ANION flow toward the anode (negative ions) 

Cathode

• Where WHAT occurs 

• Electrons flow WHERE 

• WHAT ion flow toward 

Cathode

• Where REDUCTION occurs 

• Electrons flow TOWARD the cathode  

• CATIONS flow toward (positive ions)

Electrolyte - Conduction solution → pass the WHAT around

• Active - WHAT

• Supporting - WHAT

Electrolyte - Conduction solution → pass the CHARGE around

• Active - Solution PART of RXN → contains ion in redox rxn

• Supporting - Allow CHARGE flow

What is the line notation for cells 

Anode (state) l Anode electrolyte (state) (concentration) ll Cathode electrolyte (state) (concentration)/ Cathode (state) 

Predicting E°cell

• Standard reduction potential are tabulated for common reactions 

• These are the potentials measured against a WHAT (SHE) 

• These are measured at WHAT (1M, 1bar, 25°C) 

• A positive E° is WHAT and will have an equilibrium that favours the WHAT 

• The larger the E° value the more WHAT that will be formed at equilibrium there for the reaction is favourable

Predicting E°cell

• Standard reduction potential are tabulated for common reactions 

• These are the potentials measured against a STANDARD HYDROGEN ELECTRODE (SHE) 

• These are measured at STANDARD STATE (1M, 1bar, 25°C) 

• A positive E° is SPONTANEOUS and will have an equilibrium that favours the PRODUCTS 

• The larger the E° value the more PRODUCTS that will be formed at equilibrium there for the reaction is favourable

How to predict E°cell

1. WHAT 

2. WHAT 

3. WHAT 

How to predict E°cell

1. Use a VOLTMETER to measure  

2. Calculate from REDUCTION POTENTIAL  

3. Calculate from K  

Energy and electrochemistry: What does spontaneity of a redox reaction depend on 

• WHAT 

• WHAT 

Energy and electrochemistry: What does spontaneity of a redox reaction depend on 

• # of electron being transferred (ne)  

• How easy/difficult to move ELECTRONS ( E°cell)

Energy and electrochemistry equation

ΔG = -(ne) (F) (E°cell)

E°cell > 0 → ΔG WHAT 0 therefore WHAT

E°cell < 0 → ΔG WHAT 0 therefore WHAT

E°cell > 0 → ΔG < 0 therefore SPONTANEOUS

E°cell < 0 → ΔG > 0 therefore NON-SPONTANEOUS

What factors affect the cell potential

1. WHAT

2. WHAT

What factors affect the cell potential

1. Species involved in the redox reaction

2. Concentration of species

1. Species involved in the redox reaction

Tendency of a species to gain/lose electrons

2. Concentration of species

1. Standard conditions 

2. Non-standard condition (nernst equation) 

Nernst equation

Use to determine WHAT

Nernst equation

Use to determine NON-STANDARD CELL POTENTIAL

Ecell = E°cell - (RT/neF)lnQ

When at equilibrium

• ΔG = 0

• Q = K

• Ecell = WHAT

There for equation = WHAT

• A positive value for the cell potential means that the reaction has an equilibrium that favours the WHAT (K WHAT 1) it is spontaneous in the HWAT direction

• A negative value for the cell potential means that the reaction has an equilibrium that favours the WHAT (K WHAT 1) it is spontaneous in the HWAT direction

When at equilibrium

• ΔG = 0

• Q = K

• Ecell = 0

There for equation = Ecell = (RT/neF)lnK

• A positive value for the cell potential means that the reaction has an equilibrium that favours the PRODUCTS (K > 1) it is spontaneous in the FORWARD direction

• A negative value for the cell potential means that the reaction has an equilibrium that favours the REACTANTS (K < 1) it is spontaneous in the REVERSE direction

Q <1

[products] WHAT [Reactants]

E WHAT E°

Rxn WHAT

Q <1

[products] < [Reactants]

E > E°

Rxn is going in the forward direction MORE

Q = 1

[products] WHAT [Reactants]

E WHAT E°

Rxn WHAT

Q = 1

[products] = [Reactants]

E = E°

Can be standard condition or anytime Q = 1

Q > 1

[products] WHAT [Reactants]

E WHAT E°

Rxn WHAT

Q > 1

[products] > [Reactants]

E < E°

Rxn is going in the forward direction LESS

Q = K

[products] WHAT [Reactants]

E = WHAT

Rxn WHAT

Q = K

[products] < [Reactants]

E = 0

RXN is at EQUILIBRIUM

K > 1

E°cell WHAT 0

ΔG° WHAT 0

WHAT favoured

Forward rxn is WHAT

K > 1

E°cell > 0

ΔG° < 0

PRODUCT favoured

Forward rxn is SPONTANEOUS

K < 1

E°cell WHAT 0

ΔG° WHAT 0

WHAT favoured

Forward rxn is WHAT

K < 1

E°cell < 0

ΔG° > 0

REACTANTS favoured

Forward rxn is NON-SPONTANEOUS