Oxidation = loss of electrons

Reduction = gain of electrons

(they occur together) 

Helpful to write them separately = half reactions 

• Include reactant being oxidized or reduced 

• Electrons lost = products

• Electrons gain = reactants 

EX. 

Zn(s) + 2H⁺ (aq) → Zn²⁺ (aq) + H₂(g)

• Zinc oxidized to Zn²⁺ 

  • Half reaction: Zn → Zn²⁺ + 2e⁻ (balanced in terms of zinc atoms) (there is account for loss of 2 electrons) 

• Hydrogen is reduced 

Half reaction: 2H⁺ + 2e⁻ → H₂ (balanced; charge is 0)

OVERALL REACTION is sum of half reactions

Electrons cancel out. 

*in balanced redox reactions electrons have to cancel out exactly

• Redox reactions = each individual half reaction and then combining the two balanced half reactions.

Sometimes a half reaction must have all of its coefficients multiplied by some integer for all the electrons to cancel. 

EX. BELOW

Write and balance the redox reaction that has silver ions and aluminum metal as reactants and silver metal and aluminum ions as products. 

**SOLUTION BELOW…TOO LAZY TO REWRITE..SORRY..GOTTA READ:(