What is a Redox Reaction? Notes Chemistry Class 11

A redox reaction is a chemical reaction where electrons are transferred between two substances. The word “redox” comes from two processes happening at the same time:

1. Reduction: Gain of electrons.
2. Oxidation: Loss of electrons.

Think of it as a give-and-take of electrons between two substances.

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Key Idea: Electrons are Transferred in Redox Reaction

• When one substance loses electrons (oxidation), another substance gains those electrons(reduction).
• These two processes always happen together in a redox reaction.

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How to identify a Redox Reaction?

Look for changes in oxidation numbers (a number that tells you how many electrons an atom has gained, lost, or shared). If the oxidation numbers of elements change during a reaction, it’s a redox reaction.

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Simple Example:

Let’s take the reaction between zinc (Zn) and copper sulfate (CuSO₄):Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)

What’s Happening?

1. Zinc (Zn):
   • Loses 2 electrons: Zn→Zn2++2e−Zn→Zn2++2e−.
   • This is oxidation (loss of electrons).
   • Zinc is the reducing agent (it helps reduce copper by giving electrons).
2. Copper (Cu²⁺):
   • Gains 2 electrons: Cu2++2e−→CuCu2++2e−→Cu.
   • This is reduction (gain of electrons).
   • Copper is the oxidizing agent (it helps oxidize zinc by taking electrons).

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Another Simple Example of Redox Reaction: Rusting of Iron

When iron reacts with oxygen to form rust:4Fe(s)+3O2(g)→2Fe2O3(s)4Fe(s)+3O2​(g)→2Fe2​O3​(s)

What’s Happening?

1. Iron (Fe):
   • Loses electrons: Fe→Fe3++3e−Fe→Fe3++3e−.
   • This is oxidation.
2. Oxygen (O₂):
   • Gains electrons: O2+4e−→2O2−O2​+4e−→2O2−.
   • This is reduction.

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Everyday Examples of Redox Reactions:

1. Batteries: Chemical energy is converted into electrical energy through redox reactions.
2. Rusting: Iron reacts with oxygen to form rust (iron oxide).
3. Combustion: Burning of fuels (e.g., methane) involves redox reactions.
4. Photosynthesis: Plants convert carbon dioxide and water into glucose using redox reactions.

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Quick Summary:

• Redox reactions involve the transfer of electrons.
• Oxidation = Loss of electrons.
• Reduction = Gain of electrons.
• Both processes happen simultaneously in a redox reaction.

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Mnemonic to Remember:

• OIL RIG:
  • Oxidation Is Loss (of electrons).
  • Reduction Is Gain (of electrons).