Classifying Chemical Reactions

Chemical reactions can be classified based on the pattern of the reaction:

Type of Reaction	Generic Equation
synthesis or combination	A + B → AB
decomposition	AB → A + B
single-displacement	A + BC → AC + B
double-displacement	AB + CD → AD + CB
combustion	CₓHᵧ + O₂ → CO₂ + H₂O

Synthesis Reaction

simple substances combine to form more complex substances
synthesis reaction equation: A + B → AB
examples:

2Na(s) + Cl₂(g) → 2NaCl(s)
CaO(s) + CO₂(g) → CaCO₃(s)

Decomposition Reaction

a complex substance decomposes to form simpler substances
most decomposition reaction requires energy to happen
synthesis reaction equation: AB → A + B
examples:

2HgO(s) → 2Hg(I) + O₂(g)
2KClO₃(s) → 2KCl(s) + 3O₂(g)

Single Replacement or Single Displacement Reaction

one element displaces another in a compound
single replacement reaction equation: A + BC → AC + B
examples:

Zn(s) + CuCl₂(aq) → ZnCl₂(aq) + Cu(s)
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Double Replacement or Double Displacement Reaction

2 elements or groups of elements in 2 different compounds exchange places to form 2 new compounds
double replacement reaction equation: AB + CD → AD + CB
example:

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Combustion Reaction

a hydrocarbon reacts with oxygen to produce
carbon dioxide and water during complete combustion
carbon monoxide and water during incomplete combustion when not enough oxygen is available
combustion reaction equation: CₓHᵧ + O₂ → CO₂ + H₂O
example:

CH₄ + 2O₂ → CO₂(g) + 2H₂O(g)

Example Problems

Classify each of the following reactions:

Na₂O(s) + H₂O(l) → 2NaOH
Ba(NO₃)₂(aq) + K₂SO₄(aq) → BaSO₄(s) + 2KNO₃
2Al(s) + Fe₃O₃(s) → Al₃O₃(s) + 2Fe(l)
2H₈H₁₈ + 25O₂ → 18H₂O + 16CO₂
2H₂O₂(aq) → 2H₂O(l) + O₂(g)

Answers

SYNTHESIS
DOUBLE-DISPLACEMENT
SINGLE-DISPLACEMENT
COMBUSTION
ECOMPOSITION