In a chemical reaction, one or more substances change into new/different substances

According to the Law of Conservation of Mass a skeleton chemical equation must be balanced by placing COEFFICIENTS in front of chemical formula(s)

NOTE – correct chemical formula can not be changed!!!!

Lets look at a sample reaction:

solid magnesium and hydrochloric acid react to form hydrogen gas and magnesium chloride solution

Equations are used to describe chemical reactions

Word Equation

Magnesium + hydrochloric acid hydrogen gas + magnesium chloride

Chemical Equation

Mg + 2 HCl H2 + MgCl2

Chemical Equation

Mg + 2HCl H2 + MgCl2

Reactants Products

When looking at a chemical equation, we often do not know what state the reactants or products are in

State symbols are used to indicate the physical state of the chemicals in your equation at SATP.

(s) = Solid (l) = Liquid (g) = Gas (aq) = aqueous, (dissolved in water)

Chemical equation

Mg + 2HCl H2 + MgCl2

Balanced chemical equation with state symbols

Mg(s) + 2 HCl(aq) H2(g) + MgCl2 (aq)

Although there are MILLIONS of possible chemical reactions, we

are able to use patterns to identify/predict some general

TYPES of reactions.

SynthesisSynthesis DecompositionDecomposition Single DisplacementSingle Displacement Double DisplacementDouble Displacement CombustionCombustion

(complete & (complete & incomplete)incomplete)

The direct combination of 2 substances (elements or compounds) to form a compound.

General equation:A + B → ABA and B can be elements or compounds, AB is a

compound.

EXAMPLES OF SYNTHESIS Reactions: P4 (s) + 5 O2 (g) 2 P2O5 (s)

2 Na (s) + Cl2 (g) 2 NaCl (s)

2 Al (s) + 3 I2 (g) 2 AlI3 (s)

Metal oxide + water baseNa2O(s) + H2O(l) 2NaOH(aq)

Non metal oxide + water acidCO2(g) + H2O(l) H2CO3(aq)

Decomposition Reactions- The splitting up of a larger molecule into

simpler substances (elements or compounds).

- often require heat, light or electricity 

General Equation:AB→ A + B AB is a compound, A and B can be elements or

compounds

Electrolysis of water:2 H2O (g) 2 H2 (g)+ O2 (g)

Nitrogen triiodide decomposing: 2 NI3 (s) N2 (g)+ 3 I2 (s)

Breaking down of sugarC12H22O11 (s) 12 C (s) + 11 H2O (l)

Electrolysis: the decomposition of

a compound by an electric current

Carbonate metal oxide + carbon dioxide Na2CO3(s) Na2O(s) + CO2(g)

Bicarbonate metal oxide + carbon dioxide + water

NaHCO3(s) Na2O(s) + CO2(g) +H2O(g)

Hydrate compound + water Al(NO3)3*5H2O(s) Al(NO3)3(s) + 5H2O(g)

-one element takes the place of (displaces) another element in a compound

-usually metals displace metals, and non metals displace non metals

We use the metal activity series and halogen displacement series to help us predict single displacement reactions.

General equation:A + BC → B + AC (A is a metal)orN + BC → B + CN (N is a non-metal) A, B, and N are elements/diatomic

molecules. BC, AC and CN are compounds.

EXAMPLES of Single Displacement Reactions:

2 Mg (s) + CO2 (s) C (s) + 2 MgO (s)

Cu (s) + 2 AgNO3 (aq) Cu(NO3)2 (aq) + 2 Ag (s)

thermite (steel making)Fe2O3 (s) + 2 Al (s) 2 Fe (s) + Al2O3 (s)

Metals higher on the activity series table are stronger and end up with a partner!

-Involves the displacement of “partners”-the metal cations in each reactant

exchange places, elements in different compounds displace each other or exchange places.

- a precipitate, a gas or a molecular compound is usually formed

General equation:AB + CD → AD+ CB

A,C = metal cations (simple or polyatomic cations) B,D = non metallic anions (simple or polyatomic anions )

*Remember, metals can only switch with metals, and non-metals can only switch with non-metals!

2 NaOH (aq) + Cu(NO3)2 (aq)

Cu(OH)2 (s) + 2 NaNO3 (aq)

Colour of the precipitate formed: light blue

2 NaI (aq) + Pb(NO3)2 (aq)

PbI2 (s) + 2 NaNO3 (aq)

Colour of the precipitate formed: yellow

Note – We use the solubility rules to predict the subscript of new products formed

A chemical reaction in which a substance (often hydrocarbons like

propane (C3H8), methane (CH4) and kerosene (C10H22)) reacts rapidly with OXYGEN and releases heat and light

energy.

The word equation for the COMPLETE COMBUSTION of a hydrocarbon: ΔHydrocarbon +Oxygen → Carbon Dioxide + Water Vapour

+ Energy (light & heat)

The general equation: CxHy+O2 →CO2 +H2OEg. Propane in a BBQ ΔC3H8 (g) +5 O2 (g)→3 CO2 (g)+4 H2O (g)

Incomplete Combustion occurs when there is not enough O2 available for

complete combustion produces a mixture of CO, C, CO2, and H2O vapour

depending on the oxygen supply available

Eg. Propane in a BBQ C3H8 (g) + 3O2 (g)→ CO2 (g)+ 4H2O (g) + C(s)

+CO(g)

or

C3H8 (g) + 3O2 (g)→ 4H2O (g) + C(s) + 2CO(g)

or

C3H8 (g) + 4O2 (g)→ CO2 (g)+ 4H2O (g) + 2CO(g)

or

2C3H8 (g) + 7O2 (g)→ 8H2O (g) + 6CO(g)

or

C3H8 (g) + 2O2 (g)→ 4H2O (g) + 3C(s)