Geoscience Reference
In-Depth Information
•
Combination reactions
—In a combination (or synthesis) reaction, two or more simple sub-
stances combine to form a more complex compound.
Copper (an element) + Oxygen (an element) = Copper oxide (a compound)
Note:
There are many pairs of reactants that combine to give a single product. The reactions hap-
pen when it is energetically favorable to do so.
•
Decomposition reactions
—Decomposition reactions occur when one compound breaks
down (decomposes) into two or more substances or its elements. Basically, combination
and decomposition reactions are opposites.
Hydrogen peroxide ⇒ H
2
O + O
2
•
Replacement reactions
—Replacement reactions involve the substitution of one uncom-
bined element for another in a compound. Two reactants yield two products.
Iron (Fe) + Sulfuric acid (H
2
SO
4
) = Hydrogen (H
2
) + Iron sulfate (FeSO
4
)
•
Double replacement reactions
—In a double replacement reaction parts of two compounds
exchange places to form two new compounds. Two reactants yield two products:
Sodium hydroxide + Acetic acid = Sodium acetate + Water
Key Point:
Note that these four classifications of chemical reactions are not based on the type of
bonding, which generally can be either covalent or ionic, depending on the reactants involved.
Note:
According to the law of conservation of mass, no mass is added or removed in chemical
reactions.
14.1.2.9.2 Specific Types of Chemical Reactions
•
Hydrolysis
(
hydro
, water;
lysis
, to break) is a decomposition reaction involving the splitting
of water into its ions and the formation of a weak acid or base or both.
•
Neutralization
is a double replacement reaction that unites the H
-
ion and an acid with the
OH
-
ion of a base, forming water and a salt:
Acid + Acid ⇒ Salt + Water
•
Oxidation/reduction (redox)
reactions are combination reactions, replacement, or double-
replacement reactions that involve the gain and loss of electrons (i.e., changes in valence).
Oxidation and reduction always occur simultaneously, such that one reacting species is
oxidized while the other is reduced.
Note:
When an atom, either free or in a molecule or ion, loses electrons, it is oxidized, and its oxi-
dation number increases. When an atom, either free or in a molecule or ion, gains electrons,
it is reduced, and its oxidation number decreases.
•
Chelation
is a combination reaction in which a ligand (such as a solvent molecule or simple
ion) forms more than one bond to a central ion, giving rise to complex ions or coordination
compounds.
•
Free radical reaction
is any type of reaction that involves any species with an unpaired
electron. Free radical reactions frequently occur in the gas phase. They often proceed by
chain reaction and are initiated by light, heat, or reagents. They contain unpaired electrons
(such as oxides or peroxide decomposition products) and often are very reactive.
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