Reactions

• combination reaction (תגובת הרכבה)

  • Two or more reactants combine to form a single product.
  • $\mathrm{A}+\mathrm{B}\to \mathrm{AB}$

• decomposition reaction (תגובת פירוק)

  • A single reactant breaks down into two or more products.
  • $\mathrm{AB}\to \mathrm{A}+\mathrm{B}$
  • $\mathrm{ClNa}\to \mathrm{Cl}+\mathrm{Na}$

• single displacement reaction (תגובת התמרה יחידה)

• double displacement reaction (תגובת התמרה כפולה)

• combustion reaction: A substance reacts with oxygen gas, releasing energy in the form of heat and light.

  • $\mathrm{CH}+\mathrm{O}{}_2\to \mathrm{CO}{}_2+\mathrm{H}{}_2\mathrm{O}$

Redox

• redox (reduction-oxidation, חִמצון־חיזור, חִמְזוּר) 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 $\mathrm{Cl}$ atom in $\mathrm{Cl}{}_2$ 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 $\mathrm{Na}{}^{+}$ 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 ($\mathrm{Cl}$, $\mathrm{Br}$, and $\mathrm{I}$) have an oxidation number of $-1$ in compounds, unless combined with oxygen or fluorine.
    • Ex. the oxidation number of $\mathrm{Cl}$ in the ion $\mathrm{ClO}{}_4{}^{-}$ 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:

  • $2\mathrm{Al}+\mathrm{Fe}{}_2\mathrm{O}{}_3\to \mathrm{Al}{}_2\mathrm{O}{}_3+2\mathrm{Fe}$ (thermite reaction)
    • Here, aluminum is oxidized (loses electrons) and iron is reduced (gains electrons)
  • $4\mathrm{Fe}{}_{(\mathrm{s})}+3\mathrm{O}{}_2{}_{(\mathrm{g})}\to 2\mathrm{Fe}{}_2\mathrm{O}{}_3{}_{(\mathrm{s})}$ (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