Classification of Chemical Reactions Notes

Composition (also called combination or synthesis) Two reactants combine to form one product A + B  AB Example: 3Na + P  Na3P Helpful hints An element plus another element will always be composition; if there is only one product, it has to be composition Note that composition reactions are redox reactions

Decomposition One reactant breaks down (decomposes) into two (or more) products AB  A + B Example: 2HgO  2Hg + O2 Helpful hints If there is only one reactant, it has to be decomposition Note that decomposition reactions are redox

Single Replacement (Redox) An element takes the place of a similar element (in terms of charge) in a compound A + BC  AC + B or D + BC  BD + C Examples: 3Na + AlCl3  3NaCl + Al F2 + 2NaCl  2NaF + Cl2 Helpful hints An element plus an ionic compound will usually be single replacement; there are always 2 reactants and 2 products

Single Replacement continued Hydrogen is often a participant in redox single replacement reactions The activity series or a table of standard reduction potentials must be used to determine if a s.r. redox reaction will occur

Double Replacement (Ionic) The + and – ions in two ionic compounds switch partners AB + CD  AD + CB Example: 2Na3PO4 + 3CaCl2  Ca3(PO4)2 + 6NaCl Helpful hints Two ionic compounds yield two ionic compounds; remember a + ion always goes with a – ion and the + is written first in the formulas

Combustion A hydrocarbon (a compound made up of carbon, hydrogen, and sometimes oxygen) reacts with oxygen, or burns, to give carbon dioxide plus water CxHy + O2  CO2 + H2O or CxHyOz + O2  CO2 + H2O Example: CH4 + 2O2  CO2 + 2H2O Helpful hints Oxygen is always a reactant and the products are always carbon dioxide and water! These are also redox reactions