11. CHEMICAL EQUATION
SYMBOLS AND THEIR MEANINGS
SYMBOL MEANING
To show combination of reactants or products
To produce; to form; to yield
(s), (l), (g), (aq) (s)-solid, (l)-liquid, (g)-gas, (aq)-aqueous
(substance is dissolved in water)
Reversible reaction
heat Indicates that heat is supplied to the reaction
A formula written above or below the yield
sign indicates its use as a catalyst or solvent.
Cl
12. TYPES OF CHEMICAL REACTION
1. COMBINATION REACTION
2. DECOMPOSITION REACTION
3. SINGLE DISPLACEMENT
4. DOUBLE DISPLACEMENT
5. COMBUSTION REACTION
6. ACID-BASE REACTION
13. 1. COMBINATION REACTION
A reaction in which two or more
substances combine to form a
single new substance.
Also be called synthesis reactions
General formula: A+B AB
14. A + B AB
EXAMPLE: When magnesium (Mg) burns in
air, the atoms of the metal combine with the gas
oxygen (O2) to produce magnesium oxide.
Mg (s) + O2 (g) → MgO (s)
15. 2. DECOMPOSITION REACTION
A reaction in which a compound
breaks down into two or more simpler
substances.
Most decomposition reactions require
an input of energy in the form of heat,
light, or electricity.
General Formula: AB→A+B
16. EXAMPLE: When a soda bottle is opened,
carbonic acid breaks down to produce water
and carbon dioxide, which causes the fizz.
AB→A+B
17. 3. SINGLE DISPLACEMENT
(REPLACEMENT) REACTION
Single replacement reactions are also called single
displacement reactions.
Is a chemical reactions in which a more active
element replaces a less active element in a
compound. Single replacement reactions produce a
new compound and an element as products. When
this happens a new compound is formed and an
element is released.
General Formula: A + BC → AC + B.
18. EXAMPLE: When calcium chloride
reacts with sodium, the result is
sodium chloride and calcium. Sodium
chloride is table salt.
CaCl2 + Na → NaCl + Ca
A + BC → AC + B
19. NOTE: Not all proposed single-replacement
reactions will occur between two given reactants.
This is most easily demonstrated with fluorine,
chlorine, bromine, and iodine. Collectively, these
elements are called the halogens and are in the last
column on the periodic table. The elements on top
of the column will replace the elements below them
on the periodic table but not the other way around.
20. 4. DOUBLE DISPLACEMENT
REACTION (METATHESIS)
occurs when the positive and negative ions of
two ionic compounds switch places to form
two entirely new compounds in an aqueous
solution. These compounds can come in the
form of precipitates, gasses, or molecular
compounds.
General formula: AB + CD AD + CB
21. AB + CD AD + CB
Sodium hydroxide (a base) reacts with ammonium chloride (salt)
to form sodium chloride, hydrochloric acid, and water.
NaOH + NH₄Cl = NaCl + NH₄OH
Silver nitrate reacts with sodium chloride to form silver chloride
and sodium nitrate.
AgNO₃ + NaCl = AgCl + NaNO₃
22. 5. COMBUSTION (BURNING)
REACTION
Is a reaction in which a substance reacts with oxygen gas,
releasing energy in the form of light and heat. Combustion
reactions must involve O2 as one reactant. The combustion of
hydrogen gas produces water vapor:
2H2(g)+O2(g)→2H2O(g)
Notice that this reaction also qualifies as a combination reaction.
Note that the water produced is in the gas state, rather than the
liquid state, because of the high temperatures that accompany a
combustion reaction.
23. 6. ACID-BASE REACTION
acids as substances that dissolve in water to
produce hydrogen ion (H+) in an aqueous
solution
whereas bases are defined as substances that
dissolve in water to produce hydroxide ion
(OH−) in an aqueous solution.
The H+ of the acid reacts with the OH- of the
base forming water. The other product is salt.
24. Acid-base reactions are significant in everyday life.
Calcium oxide (CaO) is used to neutralize acidic soil.
Hydrochloric acid (HCl) in the stomach plays a vital role in
digesting food.
Antacids, which are bases, are taken to neutralize excess
stomach acid, to prevent damage to the intestines.
Alkaline calcium hydroxide (limewater) is used to
absorb harmful acidic sulfur dioxide (SO2) gas that is
released from power stations and the burning of fossil
fuels.
EXAMPLES:
25. EXAMPLE:
Hydrochloric acid reacts with sodium hydroxide to form
sodium chloride (a salt) and water. Sodium chloride is made
up of Na+ cations from the base (NaOH) and Cl− anions from
the acid (HCl).
HCl (aq)+NaOH (aq)→H2O (l)+NaCl (aq)
