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Law of Conservation of MassAll chemical and physical reactions must
follow the LCM.Lavoisier was the first to state this law and
he was also given credit as the founder of quantitative chemistry.
All equations must be balanced in order to adhere to the LCM.
Law of Conservation of MassRegular reactions: atoms and masses
balanceRedox reactions: atoms, masses, and
charges balanceHere there will be change in the oxidation state of
ions during the reaction. One element will be oxidized; that means that it
will lose electrons and become more positive. One element will be reduced; that means that it
will gain electrons and become more negative. A balanced equation may require that half
reactions be considered in order to balance the charges.
Redox examplesMg0
(s) + 2HCl(aq) MgCl2(aq) + H2(g)
Half reactions: Oxidation: Mg0
(s) Mg+2 + 2e-
Reduction: 2H+(aq) + 2e- H2
0
Spectator ions: Cl-(aq)
Types of ReactionsSynthesis (direct combination) – A+BC
May use elements May use compounds
Using metal oxides: get hydroxidesUsing nonmetal oxides: get acids
Decomposition (analysis) – C A+BOrdinary binary compoundsChlorates – chloride salt and oxygenCarbonates – oxides and carbon dioxideHydroxides – metal oxide and waterAcids – nonmetallic oxide and water
ExamplesOrdinary binary compounds
2NaCl(s) 2Na0(s) + Cl20
(g)
Chlorates – chloride salt and oxygen2KClO3(s) 2KCl(s) + 3O2(g)
Carbonates – oxides and carbon dioxideBaCO3(s) BaO(s) + CO2(g)
Hydroxides – metal oxide and waterNaOH(l) Na2O(s) + H2O(l)
Acids – nonmetallic oxide and waterH2SO4(s) SO3(g) + H2O(l)
Types of ReactionsSingle displacement – A + BC AC + B
Must use activity series to determine if reaction happens
May be used with halogens with F2 > Cl2 > Br2 > I2
Double replacement – AB + CD AD + CBMust consider the driving forces to determine if
reaction happensFormation of a precipitateFormation of a gasFormation of waterFormation of a small molecular compound
Solubility RulesFormation of a precipitate occurs if the product
is insoluble in aqueous solution. Soluble compounds are those containing
NH4+, Li+1, Na+1, K+1, Rb+1, Cs+1
NO3-
C2H3O2- except with Ag+
Cl-, Br-, I- except with Ag+, Hg2+2, and Pb+2
SO4-2 except with Sr+2, Ba+2, Hg2
+2, Pb+2
Solubility Rules
Insoluble compounds are those containingS-2 except with NH4
+, Li+1, Na+1, K+1, Rb+1, Cs+1, Sr+2, Ba+2, Ca+2
CO3-2 except with NH4
+, Li+1, Na+1, K+1, Rb+1, Cs+1
PO4-3 except with NH4
+, Li+1, Na+1, K+1, Rb+1, Cs+1
OH- except with NH4+, Li+1, Na+1, K+1, Rb+1, Cs+1, Sr+2,
Ba+2, Ca+2
REMEMBERDiatomics such as H2, O2, N2, F2, Cl2, Br2, or
I2The charge on a compound must net zero.The charges on the representative
elements are predictable; those on the transition elements are not except for zinc, silver, and cadmium.
Types of ReactionsCombustion – one reactant will be oxygen
and the other one may be an organic compound, a metallic compound, or a nonmetallic compoundComplete – occurs when there is excess
oxygen CO2(g) + H2O(l)
Incomplete – occurs when there is a limited amount of oxygen CO(g) + H2O(l)
Types of Solution ReactionsPrecipitation reactions – a precipitate forms as
a result of two solutions reacting in solutionAcid-base reactions (neutralizations) – water
and a salt form as a result of an acid and a base reacting in solution (may be a titration)
Oxidation-reduction reactions (redox) – products form such that the charges on reactant ions change as the reaction proceeds. Two half reactions are sometimes required to
determine the balanced equation. May be in acidic or basic solution.
Atomic and Molecular WeightsAtomic masses are based on the standard
of carbon-12. The masses on the periodic table are not
the mass of any isotopes; they are the weighted average of all the isotopes.