Half Reactions
Half Equations
Redox reactions can be divided up into two parts, one part for reduction and one for the oxidation part. These are known as half equations
Oxidation half equation:
Reduction half equation:
Half Reactions
In electrochemistry, each half reaction requires or generates a specific amount of energy (voltage)
We can combine different half reactions together to obtain a specific amount of energy required to perform a specific function
An alkaline battery:
Half reactions:
The voltage of the two half reactions combined:
To facilitate the movement of electrons in a solution, it is common to perform the reaction in a solution that is acidic or basic.
Balancing a Half Reaction in Acidic Conditions
- Balance all atoms, except for
and - Balance
by adding - Balance
by adding - Balance the charge by adding electrons
Balance:
solution
Balance all atoms, except for
Balance
Balance
Balance the charge by adding electrons
Balance:
solution
Balance all atoms, except for
Balance
Balance
Balance the charge by adding electrons
We need 2 electrons on the right
Balancing a Half Reaction in Basic Conditions
These rules are similar to those of acidic conditions
- Balance all atoms, except for
and - Balance
by adding - Balance
by adding - ! Add
to both sides to create an equal number of present - ! Add
and together to create water, then collect like terms for water - Balance the charge by adding electrons
Balance:
solution
Balance all atoms, except for
Balance
Balance
Add
Add
Balance the charge by adding electrons
Balance:
solution
Balance all atoms, except for
Balance
Balance
Add
Add
Balance the charge by adding electrons
We need 3 electrons on the left