While oxygen gain and hydrogen loss are traditional definitions of oxidation, they are less commonly used today compared to the electron transfer definition.
Always consider the context of the reaction.
Reduction
Electron Gain: Reduction occurs when an atom or ion gains electrons.
Oxygen Loss: Reduction can also mean the removal of oxygen.
Hydrogen Gain: Reduction may involve the addition of hydrogen.
Example
Chlorine gains electrons and is reduced: $$ \text{Cl₂(g)} + 2e⁻ \rightarrow 2\text{Cl⁻(aq)} $$
Copper(II) oxide loses oxygen and is reduced: $$ \text{CuO(s)} + \text{H₂(g)} \rightarrow \text{Cu(s)} + \text{H₂O(g)} $$
Ethene gains hydrogen in this reaction: $$ \text{C₂H₄(g)} + \text{H₂(g)} \rightarrow \text{C₂H₆(g)} $$
Oxidation States: A Tool for Tracking Electron Transfers
To systematically analyze redox reactions, chemists assign oxidation states to atoms.
These numbers help track the movement of electrons in a reaction.
Rules for Assigning Oxidation States
Elements in Their Standard State: The oxidation state of an atom in its elemental form is always 0.
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Consider the hydrogenation reaction C2H4(g)+H2(g)→C2H6(g). Which statement correctly describes oxidation and reduction in this process?
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Note
Introduction to Redox Reactions
Redox reactions are chemical reactions where electrons are transferred between atoms.
They are fundamental to many natural and industrial processes.
Examples include rusting, combustion, and cellular respiration.
AnalogyThink of redox reactions like a bank transaction where electrons are the currency being transferred between accounts (atoms).
ExampleWhen iron rusts: 4Fe+3O2→2Fe2O3
Iron atoms lose electrons to oxygen atoms.NoteThe term "redox" comes from combining "reduction" and "oxidation."DefinitionRedox ReactionA chemical reaction involving the transfer of electrons between species.Common MistakeDon't assume that all redox reactions involve oxygen - electron transfer is the key aspect!
