CHEMICAL REACTIONS - Quartzland
CHEMICAL REACTIONS
Outline
I. Oxidation-Reduction Reactions
(a) Combination Reactions
(1) Reaction of non-metallic oxides
(2) Reaction of metallic oxides
(b) Decomposition Reactions
(1) Dehydration of acids
(2) Dehydration of bases
(c) Single Replacement Reaction
(d) Combustion Reactions
II. Double Replacement Reactions
(a) General Information
(b) Heat given off from reaction
(c) Formation of a Precipitate
(d) Formation of weak acid
(e) Formation of a weak base
III. Net Ionic Reactions
(a) Neutralization
(b) Formation of a precipitate
(c) Formation of weak acid or weak base
(d) Single replacement reactions
I. Oxidation-Reduction Reactions - In oxidation-reduction (Red-ox)
reactions there is a change in the oxidation states of the reactants.
This change represents a transfer of electrons from one element to
another. Useful mnemonic devices include:
"Leo" the lion said "Ger" Oil Rig
Lose electrons is oxidation (Leo) or Oxidation is loss (Oil)
Gain electrons is reduction (Ger) Reduction is gain (Rig)
A reactant is oxidized when it loses electrons and
a reactant is reduced when it gains electrons.
Red-ox nomenclature becomes really confusing when you consider that:
The reducing agent causes another substance to be reduced
(to undergo reduction) and is itself oxidized.
The oxidizing agent causes another substance to be oxidized
(to undergo oxidation) and is itself reduced.
Chemical Reactions (cont.) Page 2
Reactions which fall into this class include:
(a) Combination reactions (sometimes Red-ox)
(b) Decomposition reactions (sometimes Red-ox)
(c) Single replacement reactions (always Red-ox)
(d) Combustion reactions (always Red-ox)
(a) Combination Reactions (sometimes these reactions are Red-ox)
(1) General form of the reaction. The product of some
combination reactions can be predicted fairly easily
while other reactions are not so easy to predict.
A + B ( C
(2) Oxidation reactions (addition of oxygen)
0 0 +3 -2 ( (Notice the change of charge on the atoms)
4Al + 3O2 ( 2Al2O3 Red-ox
(3) Reaction of basic anhydrides
(metallic oxides “basic oxides” react w/ water to form bases)
+1 -2 +1 -2 +1 -2 +1 ( (Notice no change of charge on atoms)
Na2O + H2O ( 2NaOH Not Red-ox
(4) Reaction of acidic anhydrides
(non-metallic oxides “acidic oxides” react with water to form acids)
+4 -2 +1 -2 +1 +4 -2 ( (Notice no change of charge on atoms)
CO2 + H2O ( H2CO3 Not Red-ox
Chemical Reactions (cont.) Page 3
(b) Decomposition Reactions (these reactions may or may not be Red-ox Rx)
(1) General form of the reaction. Decomposition reactions are the
opposite of combination reactions. The products of these reactions are
a little more difficult to predict.
A ( B + C
(2) Oxidation-Reduction reaction
-3 +1 0 0 ( (Notice the change of charge on atoms)
2NH3 ( N2 + 3H2 Red-ox
(3) Formation of basic anhydride
+2 -2 -1 +2 -2 +1-2 ( (Notice no change of charge on atoms)
Ca(OH)2 ( CaO + H2O Not Red-ox
(4) Formation of acidic anhydride
+1 +4 -2 +1 -2 +4 -2 ( (Notice no change of charge on atoms)
H2SO3 ( H2O + SO2 Not Red-ox
(c) Single Replacement Reaction (these reactions are always Red-ox Rx)
These reactions are easily predicted with the use of a electromotive
series(activity series). Any free element (zero charge) will replace
any ion(positive charged cation) below it on the series. The examples
will not show changes in oxidation state, but you can verify these
reactions to be red-ox reactions.
(1) General form of the reaction. This reactions can be recognized by the
fact that an element is reacting with a compound to form a new element
and compound.
A + BC ( AC + B
(2) 2Na + 2H2O ( 2NaOH + H2
The seven diatomic elements (H, N, F, O, I, Cl, Br) exist in groups of
two when they are in their elemental state. An easy mnemonic device
to remember is “Have No Fear Of Ice Cold Beer”
(3) Zn + 2HCl ( ZnCl2 + H2
(4) Ca + CuSO4 ( CaSO4 + Cu
(5) Cu + HCl ( No Reaction
(Cu is below H on the Electromotive Series)
Chemical Reactions (cont.) Page 4
(d) Combustion Reactions (These are always red-ox reactions) The examples
will not show changes in oxidation state, but you can verify these
reactions are red-ox reactions.
(1) General form of the reactions. Organic compounds containing carbon,
hydrogen and/or oxygen react with excess oxygen to form carbon dioxide
and water. The assumption must be made that the reaction is complete
and the only products are CO2 and H2O.
Organic Cpd + O2 ( CO2 + H2O
(2) C (no hydrogen) + O2 ( CO2
This reaction is also a combination reaction
(3) 2H2 (no carbon) + O2 ( 2H2O
This reaction is also a combination reaction
(4) CH4 + 2O2 ( CO2 + 2H2O
(5) 2C2H6 + 7O2 ( 4CO2 + 6H2O
(6) 2CH4O + 3O2 ( 2CO2 + 4H2O
Chemical Reactions (cont.) Page 5
II. Double replacement Reactions – Double replacement reactions are never
oxidation-reduction reactions. These reactions can be predicted
to occur if heat is given off, a precipitate forms or a gas is given off.
(a) General form of the reaction. This reactions can be recognized by the fact that
two compounds react to form two new compounds.
AB + CD ( AD + CB
(b) Heat evolved: These reactions are usually neutralization reactions.
In these reactions an acid and base react to form a salt and water in the
process giving off heat. Neutralization reactions always occur making them
easy to predict.
(1) Acid + Base ( Salt + Water
(2) H+ A + B OH- ( BA + HOH
(3) HCl + NaOH ( NaCl + HOH
(4) 3H2SO4 + 2Al(OH)3 ( Al2(SO4)3 + 6H2O
(c) Formation of a Precipitate: In these reactions two soluble salts
react to form an insoluble salt. These reactions are very
difficult to predict unless a solubility chart is available.
(1) AgNO3 + NaCl ( AgCl + NaNO3
(Any of these symbols can indicate a precipitate; AgCl, AgCl , or AgCl(s))
(2) BaCl2(aq) + H2SO4(aq) ( BaSO4(s) + 2HCl(aq)
Chemical Reactions (cont.) Page 6
(d) Formation of weak acid: This type of reaction includes reactions where
a gas is evolved, but is not limited to such cases. A strong acid reacts
with the salt of a weak acid to form the un-ionized weak acid and the
salt of a strong acid.
(1) Salt of Weak + Strong ( Salt of + Weak
Strong acids - HCl, HClO4, HI, H2SO4 and HNO3
Weak acids - all the other acids; i.e. H2CO3, HC2H3O2,
1
Acid Acid Strong Acid Acid
(2) Na2CO3 + 2HCl ( H2CO3 + 2NaCl
(H2CO3 ( H2O + CO2(g))
( CO2 or CO2(g) indicates a gas)
(3) NaC2H3O2 + HCl ( HC2H3O2 + NaCl
(e) Formation of a weak base. This type of reaction encompasses reactions where
a gas is evolved but is not limited to such cases. A strong base reacts with
the salt of a weak base to form the un-ionized weak base and the salt of
a strong base.
Strong Bases - Group IA or IIA metal hydroxides i.e. NaOH, Ca(OH)2
Weak Base - All the other bases i.e. Fe(OH)3, NH4OH)
2
(1) Salt of Weak + Strong ( Salt of + Weak
Base Base Strong Base Base
(2) NH4Cl + NaOH ( NH4OH + NaCl
(NH4OH ( NH3(g) + H2O)
(3) FeCl3 + 3KOH ( Fe(OH)3 + 3KCl
Chemical Reactions (cont.) Page 7
III. Net Ionic Reactions - Reactions of this type are concerned with only
those atoms, molecules or ions that are actually involved in the
reactions. All spectator ions (ions not actually involved in the
reaction) are removed from the reaction. The active species of a
reaction are easily identified when ionic reactants go to molecular
species (and vice versa) or when there is a change in oxidation states
between reactants and products.
(a) Neutralization
NaOH + HCl ( NaCl + HOH General Reaction
NaOH(aq) + HCl(aq) ( NaCl(aq) + HOH(l) Molecular Reaction
Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) ( Na+(aq) + Cl-(aq) + HOH(l) Ionic Reaction
OH-(aq) + H+(aq) ( HOH(l) Net Ionic Reaction
For neutralization reactions the net ionic reaction has no spectator ions,
Na+(aq) and Cl-(aq). The spectator ions can be replaced with other ions that
provide the needed acid (H+(aq)) and base (OH-). For example in H2SO4 and Al(OH)3
the spectator ions would be SO4-2(aq) and Al+3(aq) and the H+(aq) and OH-(aq) are still
the major reactants in the net ionic reaction.
(b) Formation of a precipitate
AgNO3 + NaCl ( AgCl + NaNO3 General Reaction
AgNO3(aq) + NaCl(aq) ( AgCl(s) + NaNO3(aq) Molecular Reaction
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) ( AgCl(s) + Na+(aq) + NO3-(aq) Ionic Reaction
Ag+(aq) + Cl-(aq) ( AgCl(s) Net Ionic Reaction
In precipitation reactions the net ionic reactions does not show the spectator
ions, (NO3-(aq) and Na+(aq)).
Chemical Reactions (cont.) Page 8
(c) Formation of weak acid or weak base
NaC2H3O2 + HCl ( NaCl + HC2H3O General Reaction
NaC2H3O2(aq) + HCl(aq) ( NaCl(aq) + HC2H3O2(aq) Molecular Reaction
Na+(aq) + C2H3O2-(aq) + H+(aq) + Cl-(aq) ( Na+(aq) + Cl-(aq) + HC2H3O2(aq) Ionic Reaction
C2H3O2-(aq) + H+(aq) ( HC2H3O2(aq) Net Ionic Reaction
Whenever a weak acid (or weak base) is formed from the salt of a weak acid (or the
salt of weak base) then a net ionic reaction can be written. Remember to remove the
spectator ions, Na+(aq) and Cl-(aq). The HC2H3O2 is weak acid and is not ionic when in
aqueous solutions. See Section II.D. for weak acids and bases.
(d) Single replacement reactions
3Ca + 2FeCl3 ( 3CaCl2 + 2Fe General Reaction
3Ca(s) + 2FeCl3(aq ( 3CaCl2(aq) + 2Fe(s) Molecular Reaction
3Ca(s) + 2Fe+3(aq) + 6Cl-(aq) ( 3Ca+2(aq) + 6Cl-(aq) + 2Fe(s) Ionic Reaction
3Ca(s) + 2Fe+3(aq) ( 3Ca+2(aq) + 2Fe(s) Net Ionic Reaction
In this net ionic reaction, there is a change in oxidation state for the calcium and
iron. The chloride does not change oxidation state and is consequently not involved
in the reaction (The chloride ion is called a spectator ion).
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