Chemical Equations

A chemical equation represents a reaction using symbols, formatted as: Reactants $\rightarrow$ Products.

General Reaction Formulas:

• $\text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen}$
• $Metal~oxide + Acid \rightarrow Salt + Water$
• $Hydroxide + Acid \rightarrow Salt + Water$
• $Carbonate + Acid \rightarrow Salt + Carbon~dioxide + Water$
• $\ce{\text{Ammonium salt} + \text{alkali} -> \text{salt} + \text{ammonia gas} + \text{water}}$

decomposition reactions

• metal carbonates
  • group 1 metal carbonates do not decompose as they are too thermally stable and will just melt
    • except lithium, which still decomposes
  • $\ce{MCO3(s) ->[heat] MO(s) + CO2(g)}$
• Metal nitrates
  • group 1 metals
    • $\ce{2KNO3(s) ->[heat] 2KNO2(g) + O2(g)}$
  • group 2 & most transition metals
    • $\ce{M(NO3)2(s) ->[heat] 2MO(s) + 4NO2(g) + O2(g)}$
  • unreactive transition metals (e.g. $\ce{Ag}$, $\ce{Hg}$)
    • decompose to pure metal
      • $\ce{2AgNO3(s) ->[heat] 2Ag(s) + 2NO2(g) + O2(g)}$
• Metal hydroxides
  • most transition metals and group 2 hydroxides
    • $\ce{M(OH)2(s) ->[heat] MO(s) + H2O(g)}$
  • Group 1 metal hydroxides
    • Too thermal stable and will just melt
    • except $\ce{Li2CO3}$ it will decompose

State Symbols:

• (s): Solid
• (l): Liquid
• (g): Gas
• (aq): Aqueous (dissolved in water)

Solubility Rules

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Soluble in Water:

• Group 1 & Ammonium: All Sodium ($Na^{+}$), Potassium ($K^{+}$), and Ammonium ($NH_{4}^{+}$) compounds.
• Nitrates: All Nitrate ($NO_{3}^{-}$) salts.
• Acetates: All Acetate ($\ce{Ch3COO-}$) salts
• Chlorides/Iodides/bromides: All $Cl^{-}$, $I^{-}$ and $\ce{Br-}$ salts EXCEPT Silver ($Ag^{+}$) and Lead(II) ($Pb^{2+}$).
• Sulfates: All $SO_{4}^{2-}$ salts EXCEPT Calcium ($Ca^{2+}$), Barium ($Ba^{2+}$), and Lead(II) ($Pb^{2+}$).

Insoluble in Water:

• Oxides All $O^{2-}$ and $OH^-$ compounds EXCEPT Group 1 elements and Group 2 elements below Calcium($\ce{CA}$). (Note: Calcium Oxide ($\ce{CaO}$) and Calcium Hydroxide ($\ce{Ca(OH)2}$) are sparingly soluble)
• Carbonates: All $CO_{3}^{2-}$ compounds EXCEPT Group 1 elements and Ammonium ($NH_{4}^{+}$).
• Phosphates & Sulfides: All $\ce{PO4^3-}$ and Sulfides ($\ce{S2^-}$) EXCEPT group1 elements and ammonium

Ionic Equations

An ionic equation shows only the actual reacting species.

• Spectator Ions: Ions that do not participate in the reaction (they remain in the same state on both sides of the equation) are cancelled out.
• Chemical species that are insoluble (solids, liquids, gases) are not split into ions in the equation. Only split aqueous (aq) species.
• e.g.

Chemical equation: $\text{PbCO}_3\text{ (s)} + 2\text{HNO}_3\text{ (aq)} \rightarrow \text{Pb(NO}_3)_2\text{ (aq)} + \text{CO}_2\text{ (g)} + \text{H}_2\text{O (l)}$

Ionic equation: $\text{PbCO}_3\text{ (s)} + 2\text{H}^+\text{ (aq)} \rightarrow \text{Pb}^{2+}\text{ (aq)} + \text{CO}_2\text{ (g)} + \text{H}_2\text{O (l)}$