Introduction to Types of
Chemical Reactions
AP/ECE Chemistry
Mrs. Pesko
2
What is a Chemical Equation?
• A chemical equation uses chemical symbols to denote what occurs in a
chemical (or physical) change
NH3 + HCl → NH4Cl
• We can state a chemical equation in words: “Ammonia and hydrogen
chloride react to produce ammonium chloride.”
• Each chemical species that appears to the left of the arrow is called a
reactant.
• Each chemical species that appears to the right of the arrow is called a
product.
• The relative numbers of reactants and product
species are represented with coefficients.
• Usually smallest whole number ratio
• A coefficient of 1 is typically omitted.
Chemical Equation Symbolism
• Labels are used to indicate the physical state of reactants and
products:
▫ (g) gas
▫ (l) liquid
▫ (s) solid
▫ (aq) aqueous [Chemical species dissolved in water]
• NH3(g) + HCl(g) → NH4Cl(s)
• CaCO3(s)
D CaO(s) + CO (g)
→
2
Balancing Chemical Equations
▫
A balanced chemical equation has
equal numbers of atoms of each
element on the reactants and product
side.

The law of the conservation of matter must be
obeyed.
Balancing Chemical Equations
▫
Balancing requires a trial and error approach.
▫
Only the coefficients can be changed

Subscripts are fixed and cannot be changed.

Also, can’t add additional reactants or
products.
▫
The following tips may help when balancing a
chemical equation:

For atoms in compounds, it is best to first balance
those atoms that only appear in one species.

It is helpful to balance pure elements last.

If a polyatomic ion remains intact, then treat as a unit.
On to the Next…What’s on Today’s
Agenda?
• We will begin investigating the different types of
chemical reactions which will lead us in answering
two questions that are a central focus in chemistry:
▫ When two substances are mixed, will a chemical reaction
occur?
▫ If a chemical reaction occurs, what will the products be?
• By recognizing general patterns of chemical
reactivity, you will be able to successfully predict the
products formed by a given combination of reactants
▫ Gives a broader understanding than merely memorizing
a large number of unrelated reactions
Basic Types of Reactions
• Most chemical reactions can be classified
as being one of 5 basic types:
• Combination (synthesis)
• Decomposition
• Combustion
• Double Replacement
• Single Replacement
Combination Reactions
• Two or more substances combine to form
a single, more complex compound
• Many elements react with one another in
this fashion to form compounds
• Has the general equation:
A + X  AX
Combination Reactions
• A combination reaction between a metal and non-metal
products an ionic solid
• Use most common oxidation numbers to predict the
formula of the new compound.
▫ Example:
2Mg (s) + O2 (g)  2MgO (s)
• If 2 or more simple compounds react, they follow
common patterns:
• Nonmetal oxides + Water  Acids
CO2 (g) + H2O (l)  H2CO3 (aq)
• Metal oxides + Water  Bases
CaO (s) + H O (l)  Ca(OH) (aq)
Decomposition Reactions
• One substance breaks down into simpler
compounds or elements
• Has the general equation:
AX  A + X
• Often occurs when compounds are heated
or electricity is added
• Example:
2HgO (s)  2Hg (l) + O2 (g)
Decomposition Reaction
• Common reactivity patterns of decomposition reactions:
▫ Metal chlorates → Metal chlorides + O2
2KClO3  2KCl + 3O2
Mg(ClO3)2  MgCl2 + 3O2
▫ Metal carbonates → Metal oxides + CO2
Na2CO3 → Na2O + CO2
▫ Metal hydroxides → Metal oxides + H2O
Cu(OH)2 (s) → CuO (s) + H2O (g)
• Binary compounds → 2 elements
2 NaN3 (s) → 2 Na (s) + 3 N2 (g)
• Oxyacids → Non-metal oxide + H2O
2HNO3 (aq) → H2O (l) + N2O5 (g)
• Some metal oxides → Metal + O2 (or metal oxide)
• Ammonium hydroxide → Ammonia + H2O
Combustion Reactions
• Organic hydrocarbons, CxHy , burn in oxygen to form carbon
dioxide and water vapor
▫ Heat is also produced
• General equation:
CxHy + O2 → ___CO2 (g) + ___H2O (g)
• Example is the burning of propane:
C3H8(g)+ 502(g) -->3CO2(g)+ 4H2O(l)
• Incomplete combustion may result in carbon monoxide and
carbon soot