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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