Reactions

• Combination Reaction: Two or more reactants combine to form a single product.
  • $\text{ce}A+B->AB$
• Decomposition Reaction: A single reactant breaks down into two or more products.
  • $\text{ce}AB->A+B$
  • $\text{ce}ClNa->Cl+Na$
• Combustion Reaction: A substance reacts with oxygen gas, releasing energy in the form of heat and light.
  • $\text{ce}CH+O2->CO2+H2O$

Redox (Oxidation-Reduction)

• Redox (reduction-oxidation) is a type of chemical reaction in which the oxidation states of the reactants change.

  • Oxidation: Loss of electrons (oxidation state increases)
  • Reduction: Gain of electrons (oxidation state decreases)

• Oxidizing Agent: The reactant that gains electrons

• Reducing Agent: The reactant that loses electrons

• oxidation number (or oxidation state)

  • An atom of a free element has an oxidation number of $0$.
    • Ex. Each $\text{ce}Cl$ atom in $\text{ce}Cl2$ has an oxidation number of $0$.
  • The oxidation number of a monatomic ion is equal to the charge of the ion.
    • Ex. The oxidation number of $\text{ce}Na+$ is $+1$
  • When combined with other elements, alkali metals have an oxidation number of $+1$ and alkaline earth metals have an oxidation number of $+2$.
  • Fluorine has an oxidation number of $-1$ in all its compounds.
  • Hydrogen has an oxidation number of $+1$ in most of its compounds.
  • Oxygen has an oxidation number of $-2$ in most of its compounds.
  • The other halogens ($\text{ce}Cl$, $\text{ce}Br$, and $\text{ce}I$) have an oxidation number of $-1$ in compounds, unless combined with oxygen or fluorine.
    • Ex. the oxidation number of $\text{ce}Cl$ in the ion $\text{ce}ClO4-$ is $+7$.
  • The sum of the oxidation numbers in a neutral compound is $0$.
  • The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.

• Examples:

  • $\text{ce}2Al+Fe2O3->Al2O3+2Fe$ (thermite reaction)
    • Here, aluminum is oxidized (loses electrons) and iron is reduced (gains electrons)
  • $\text{ce}4F{e}_{(s)}+3O{2}_{(g)}->2Fe2O{3}_{(s)}$ (rusting of iron)
    • Here, iron is oxidized (loses electrons) and oxygen is reduced (gains electrons)

todo https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:chemical-reactions/x2eef969c74e0d802:oxidation-reduction-redox-reactions/a/oxidation-number