Identifying Types of Chemical Reactions

Synthesis (Combination) Reactions Synthesis: A synthesis reaction is when two or more elements or simple compounds combine to form a more complicated one. These reactions come in the general form of: A + B → AB Element or Compound + Element or Compound → Compound Combination of iron and sulfur to form iron (II) sulfide: 8 Fe + S8 → 8 FeS The combustion of hydrogen gas with oxygen to form water: 2 H2 + O2 → 2 H2O

Decomposition Reactions Decomposition: A decomposition reaction is the opposite of a synthesis reaction - a complex compound breaks down to make elements or simpler compounds. These reactions come in the general form: AB → A + B Compound → element or compound + element or compound The electrolysis of water to make oxygen and hydrogen gas: 2 H2O → 2 H2 + O2

Single Displacement Reactions Single displacement (or replacement): This is when one element trades places with another element in a compound. These reactions come in the general form of: A + BC → AC + B Element + Compound → Compound + Element Magnesium displaces hydrogen in water to make magnesium hydroxide and hydrogen gas: Mg + 2 H2O → Mg(OH)2 + H2 Zinc displaces Hydrogen in hydrochloric acid to produce Zinc chloride and hydrogen gas: Zn + 2 HCl → ZnCl2 + H2

Double Displacement Reactions Double displacement (or replacement): This is when the anions and cations of two different ionic substances exchange places, forming two entirely different compounds. These reactions are in the general form: AB + CD → AD + CB Compound + Compound → Compound + Compound Lead (II) nitrate with Potassium iodide to form Lead (II) iodide and Potassium nitrate: Pb(NO3)2 + 2 KI → PbI2 + 2 KNO3 Hydrochloric acid with Sodium hydroxide to form Sodium chloride (table salt) and water: HCl + NaOH → NaCl + H2O

Combustion Reactions Combustion: A combustion reaction is when oxygen combines with another substance to form simpler oxygen containing compounds like water and carbon dioxide. These reactions are exothermic, meaning they produce heat. If the hydrocarbon has other elements in it like nitrogen and/or sulfur it can produce additional oxygen containing products like SO2, NO2, and SO3, etc. Incomplete combustion (ie. when oxygen is in short supply) can produce CO. Substances will also combust in the presence of strong oxidizers like fluorine producing fluorine compounds. Hydrocarbon + Oxygen → Carbon dioxide + Water Combustion of napthalene: C10H8 + 12 O2 → 10 CO2 + 4 H2O

Types of Reactions Summary Synthesis (S): E/C + E/C+ … → C Decomposition (D): C → E/C + E/C + … Single Displacement (SD): E + C → E + C Double Displacement (DD): C + C → C + C Combustion (C): C + O2 → CO2 + H2O Precipitation (ppt): C(aq)+C(aq) → C(s) + C(aq) Acid/Base Neutralization: Acid + Base → a Salt + Water Redox Reaction: oxidaiton + reduction

Other Important Reactions Acid/Base Neutralization: A subcategory of double displacement reactions where an… Acid + Base → a Salt + Water Precipitation Reactions: A subcategory of double displacement reactions where one the products is an insoluble salt resulting in its precipitation from solution. Oxidation-Reduction Reactions: There is an exchange of electrons between two elements. One element loses electrons to become more positive (oxidized) and another element takes on electrons to become more negative (reduced).