(SHORT) Balancing Redox Reactions and Half Equations
Key Terms/Concepts
Redox Reaction: A chemical reaction involving the transfer of electrons between two species, where one is oxidized (loses electrons) and the other is reduced (gains electrons).
Oxidation: The process of losing electrons, resulting in an increase in oxidation state.
Reduction: The process of gaining electrons, resulting in a decrease in oxidation state.
Balancing Half-Reactions: The method of balancing redox reactions by separating them into oxidation and reduction half-reactions.
Key Equations
Equation | Description |
|---|---|
Cr₂O₇²⁻ + 14 H⁺ → 2 Cr³⁺ + 7 H₂O | Example of balancing a redox reaction by adding protons and water to balance hydrogen and oxygen. |
Cu → Cu²⁺ + 2 e⁻ | Oxidation half-reaction showing copper losing electrons. |
Ag⁺ + e⁻ → Ag | Reduction half-reaction showing silver gaining electrons. |
2 Ag⁺ + Cu → 2 Ag + Cu²⁺ | Full ionic equation combining the oxidation and reduction half-reactions. |
Key Rules for Balancing Redox Reactions
Balance Atoms Other Than O and H First: Ensure that all other elements are balanced before addressing oxygen and hydrogen.
Balance Oxygen by Adding Water: If there are oxygen atoms that need balancing, add water (H₂O) to the side that requires oxygen.
Balance Hydrogen by Adding Protons: Add H⁺ ions to the side that requires hydrogen.
Add Electrons to Balance Charges: Determine the total charge on both sides and add electrons to the more positive side to balance the charges.
Key Examples
Example of Balancing: For the reaction Cr₂O₇²⁻ + 14 H⁺ → 2 Cr³⁺ + 7 H₂O, you add 14 H⁺ to balance the hydrogen and 7 H₂O to balance the oxygen.
Example of Oxidation and Reduction: In the reaction Cu + 2 AgNO₃ → 2 Ag + Cu(NO₃)₂, copper is oxidized to Cu²⁺ while silver ions are reduced to silver metal.
Key Notes on Electron Transfer
Electrons are Denoted as e⁻: In redox reactions, electrons are represented by the symbol e⁻.
Oxidation State Changes: Keep track of the oxidation states of elements to determine which are oxidized and which are reduced.
Facts to Memorize
Oxidation is the loss of electrons.
Reduction is the gain of electrons.
Balancing Rule 1: Balance H by adding H+.
Balancing Rule 2: Balance O by adding H2O.
Balancing Rule 3: Add electrons to the most positive side.
Reference Information
Common oxidation states:
Cu: +1, +2
Ag: +1
Cr: +3, +6
Common compounds:
AgNO3 (Silver Nitrate)
Cr2O7^2- (Dichromate Ion)
States of matter:
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous (dissolved in water)