Redox Reactions

Definition

Redox reactions: Reactions in which oxidation and reduction occur simultaneously.
Oxidation: Increase in oxidation state.
Reduction: Decrease in oxidation state.

100: Represents increase in oxidation state (Oxidation).
- Example: Sodium (Na) loses one electron ➜ Na⁺ (oxidation state increases from 0 to +1).
DOOR: Represents decrease in oxidation state (Reduction).
- Example: Chlorine (Cl) gains one electron ➜ Cl⁻ (oxidation state decreases from 0 to -1).

Four rules to instantly calculate oxidation state and recognize redox reactions (previously discussed in another video):

Element in free state: Oxidation state is 0.
In combined state:
- Halogens generally: -1
- Oxygen generally: -2
- Others include well-known charge states from chemistry rules

Calcium (Ca) and Bromine (Br): Ca + Br₂ ➜ CaBr₂
- Free state: Ca = 0, Br = 0
- Combined state: Br = -2 (since each Br is -1 in combined state)
  - Calculation: Br₂ ➜ -1 + -1 = -2
  - CaBr₂ balance: Overall charge is 0; Ca must be +2
- Observations:
  - Ca: 0 ➜ +2 (oxidized)
  - Br: 0 ➜ -2 (reduced)
- Conclusion: Redox reaction.
Carbon (C) and Oxygen (O₂): C + O₂ ➜ CO₂
- Free state: C = 0, O₂ = 0
- Combined state: O in CO₂ = -2 per oxygen; -2 * 2 = -4
  - CO₂ balance: Overall charge is 0; C must be +4
- Observations:
  - C: 0 ➜ +4 (oxidized)
  - O: 0 ➜ -4 (reduced)
- Conclusion: Redox reaction.
Hydrogen (H₂) and Fluorine (F₂): H₂ + F₂ ➜ 2 HF
- Free state: H₂ = 0, F₂ = 0
- Combined state: F in HF = -1; HF neutral
  - HF balance: Each H must be +1
- Observations:
  - H: 0 ➜ +1 (oxidized)
  - F: 0 ➜ -1 (reduced)
- Conclusion: Redox reaction.

Redox reactions involve one species being oxidized (increase in oxidation state) and the other being reduced (decrease in oxidation state).
Use the trick (100/DOOR) and rules to determine the oxidation states and recognize redox reactions easily.