Electrochemistry

What is electrochemistry?

The study of the interchange of chemical and electrical energy

What are redox reactions or oxidation reduction reactions?

Reactions with electron transfer

What are examples of redox reactions?

Combustion, batteries, rusting, photosynthesis, cellular respiration, single replacement

What are examples of non redox reactions?

Neutralization, double replacement, precipitation

What is an oxidation number?

The real or apparent charge of an atom or ion

What are the rules for assigning oxidation numbers?

1. Atoms in elemental form have a charge of zero

2. The oxidation number of a monatomic ion is the charge of the ion

3. The oxidation number of F is -1 in all compounds

4. The oxidation number of H is usually +1 when bonded to non metals and -1 when bonded to metals

5. The oxidation number of O is usually -2 in most ionic and molecular compounds

6. Oxidation numbers in a neutral compound must add to zero

7. Oxidation numbers in a polyatomic ion must add to its overall charge

8. The more electronegative element should have a negative charge

What is the exception to the O rule of assigning oxidation numbers?

The oxidation number of O is usually -2 in most ionic and molecular compounds

Exceptions where O is -1 is H₂O₂ and OF₂

What is oxidation and what happens to the oxidation number?

Electrons are lost

Oxidation number increases when comparing reactants and products

What is reduction and what happens to the oxidation number?

Electrons are gained

Oxidation number decreases when comparing reactants and products

What is the reducing agent?

A species being oxidized causes the other species to gain electrons = a substance that is being oxidized acts as a reducing agent

What is an oxidizing agent?

A species being reduced causes the other species to lose electrons = a substance that is being reduced acts as an oxidizing agent

What is a half reaction?

An equation representing either an oxidation or reduction, including the number of electrons lost or gained

What are the steps to balancing half reactions?

1. Balance major atoms (other than H or O)

2. Balance the oxygen atoms by adding H₂O

3. Balance the hydrogen atoms by adding H⁺

4. Balance the charge by adding e-

5. Check your work by calculating the oxidation number

If it’s stated that the reaction happens in basic conditions:

6. Add OH^- to both sides to neutralize H⁺

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How do you balance redox reactions?

1. Separate the redox reaction into half reactions

2. Balance each half reaction

3. Multiply each half reaction to balance the transfer of electrons

4. Add half reactions together, cancelling anything that’s the same on both sides

5. If basic, add OH^- to both sides

What is a disproportionation reaction?

A redox reaction in which the same species is both reduced and oxidized

Since there is only one reactant, the reactant must be involved in both the reduction and oxidation reaction

What is the potential of oxidizing agents to be reduced called?

Its potential to be reduced is called its reduction potential

What is the potential for a reducing agent to be reduced called?

Its potential to be reduced is called its oxidation potential

What does the double arrow on the SRP table imply?

The half reactions are written as reductions but they can be written as oxidation reactions

What are the two ways to predict if reactions are spontaneous?

1. Total cell potential

2. Relative position of RA and OA on the SRP table

How do you determine the amount of voltage that can be generated from the chemical reactions?

By adding up the reduction/oxidation potential from the half reactions

If a redox reaction is spontaneous, is the reverse reaction spontaneous or non spontaneous?

Non spontaneous

If a half reaction is reversed, what happens to the E⁰ value?

The sign is reversed

What is the concentration of solutions on the SRP table?

The concentrations of all solutions are 1M except for neutral water as an OA and RA

How do you predict which species will react if there are more than 2 available?

When there are more than 2 species available to react, the SRP table is used to predict which species will recact

What is the predominant redox reaction between?

The strongest OA and strongest RA