 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 H 2 + MgCl 2

Chemical Equation Mg + 2HCl H 2 + MgCl 2  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 H 2 + MgCl 2 Balanced chemical equation with state symbols Mg (s) + 2 HCl (aq) H 2(g) + MgCl 2 (aq)

Although there are MILLIONS of possible chemical reactions, we are able to use patterns to identify/predict some general TYPES of reactions.

SynthesisDecomposition Single Displacement Double Displacement Combustion (complete & incomplete)

The direct combination of 2 substances (elements or compounds) to form a compound. General equation: A + B → AB A and B can be elements or compounds, AB is a compound.

EXAMPLES OF SYNTHESIS Reactions: P 4 (s) + 5 O 2 (g)  2 P 2 O 5 (s) 2 Na (s) + Cl 2 (g)  2 NaCl (s) 2 Al (s) + 3 I 2 (g)  2 AlI 3 (s)

Metal oxide + water  base Na 2 O (s) + H 2 O (l)  2NaOH (aq) Non metal oxide + water  acid CO 2(g) + H 2 O (l)  H 2 CO 3(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 H 2 O (g)  2 H 2 (g) + O 2 (g) Nitrogen triiodide decomposing: 2 NI 3 (s)  N 2 (g)+ 3 I 2 (s) Breaking down of sugar C 12 H 22 O 11 (s)  12 C (s) + 11 H 2 O (l) Electrolysis: the decomposition of a compound by an electric current

 Carbonate  metal oxide + carbon dioxide  Na 2 CO 3(s)  Na 2 O (s) + CO 2(g)  Bicarbonate  metal oxide + carbon dioxide + water  NaHCO 3(s)  Na 2 O (s) + CO 2(g) +H 2 O (g)  Hydrate  compound + water  Al(NO 3 ) 3 *5H 2 O (s)  Al(NO 3 ) 3(s) + 5H 2 O (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) or N + 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) + CO 2 (s)  C (s) + 2 MgO (s) Cu (s) + 2 AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2 Ag (s) thermite (steel making) Fe 2 O 3 (s) + 2 Al (s)  2 Fe (s) + Al 2 O 3 (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(NO 3 ) 2 (aq)  Cu(OH) 2 (s) + 2 NaNO 3 (aq) Colour of the precipitate formed: light blue 2 NaI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2 NaNO 3 (aq) Colour of the precipitate formed: yellow Note – We use the solubility rules to predict the subscript of new products formed

Combustion

A chemical reaction in which a substance (often hydrocarbons like propane (C 3 H 8 ), methane (CH 4 ) and kerosene (C 10 H 22 ) ) reacts rapidly with OXYGEN and releases heat and light energy.

The word equation for the COMPLETE COMBUSTION of a hydrocarbon: Δ Hydrocarbon +Oxygen → Carbon Dioxide + Water Vapour + Energy (light & heat) The general equation: C x H y +O 2 →CO 2 +H 2 O Eg. Propane in a BBQ Δ C 3 H 8 (g) +5 O 2 (g)→3 CO 2 (g) +4 H 2 O (g)

Incomplete Combustion occurs when there is not enough O 2 available for complete combustion produces a mixture of CO, C, CO 2, and H 2 O vapour depending on the oxygen supply available

 Eg. Propane in a BBQ  C 3 H 8 (g) + 3O 2 (g) → CO 2 (g) + 4H 2 O (g) + C (s) +CO (g)  or  C 3 H 8 (g) + 3O 2 (g) → 4H 2 O (g) + C (s) + 2CO (g)  or  C 3 H 8 (g) + 4O 2 (g) → CO 2 (g) + 4H 2 O (g) + 2CO (g)  or  2C 3 H 8 (g) + 7O 2 (g) → 8H 2 O (g) + 6CO (g)  or  C 3 H 8 (g) + 2O 2 (g) → 4H 2 O (g) + 3C (s)