Chemical reactions involve the transformation of one or more substances into different substances and can be represented by chemical equations. Chemical equations show the reactants on the left and products on the right of the arrow and must be balanced according to the law of conservation of mass. There are several types of chemical reactions including combination reactions where two or more substances combine to form one product, decomposition reactions where one compound breaks down into multiple products usually with heat, and substitution reactions where a more reactive metal displaces a less reactive one.

1. Chemical Reactions and Equations
by: Prof. Liwayway Memije-Cruz

2. Chemical Reaction

3. Chemical Reactions
• all about chemical change. The ripening of fruits,
photosynthesis, tarnishing of iron, burning of
woods, digestion of foods, and even cooking
foods are few examples of chemical changes
and chemical reactions happening around us
and even inside our bodies.
• it involves the transformation of one or more
substances into another substance or
substances. it involves a change in composition
and is represented by a chemical equation.

4. Chemical Equations
• Provide a concise picture of a chemical change. It is used to
convey the pertinent information about the chemical reaction which
includes the substances involved and their quantitative ratio.
• are representations of chemical reactions in terms of symbols of
elements and formulas of compounds involved in the reactions. The
substances that enter into a chemical reaction are
called reactants and the substances formed are the products.

5. Steps in Writing a Balance Equation
• Write the symbols and formulas of the
reactant/s on the left side of the arrow and
symbol/s and formula/s of the products on
the right. Monoatomic elements are
represented by their symbols without
subscript. Examples: Ca, Mg and Zn.
Diatomic elements are represented by
their symbols with subscript 2.
Examples: H2, O2, N2, F2, CI2, Br2 and I2

6. Law of Conservation of Mass
Chemical changes occur in accordance with
the Law of Conservation of Mass. It is therefore
necessary to balance the number of atoms of
each element in the reactants with the number
of atoms of the same element in the product.
Balancing chemical equations by inspection
simply requires placing the coefficient before
any of the symbol/s and formula/s until there are
exactly the same numbers of each kind of atom
on both sides of the equation.

7. Pointers to consider in using coefficient:
1. There is no need to write a coefficient, which is
1.
2. Use simplest whole numbers as coefficients.
Example:
• Write the balance chemical equation for the
reaction of hydrogen with oxygen to produce
water.
2 H2 + O2 = 2H2O
“The reaction of 2 moles of hydrogen and 1
mole of oxygen yields 2 moles of water”.

9. Types of Chemical Equations

10. Combination
 is a type of reaction in which two or
more substances (either elements or
compounds) react to form one product.
Example: 2 Na + Cl2 → 2NaCl

11. Combination Reaction

12. Combination Reaction

13. Decomposition
a type of reaction in which one
compound decomposes to
form two or more new
substances. Usually heat is to
cause these reactions to take
place.

16. Types of Decomposition Reaction
• a. Hydrates - when heated, decompose to
yield water and anhydrous salt.
A hydrate is a salt that contains one or
more molecules of water for each formula
unit of salt, built right into the crystal
structure.
Example: BaCl2 2H2O → BaCl2 + 2H2O

17. b. Chlorates – when heated, decompose to
form chlorides and oxygen gas.
Example: 2KCIO3 → 2KCI + 3O2
c. A few metal oxides decompose when
heated to form the free metal and oxygen
gas.
Example: 2HgO → 2Hg + 02

18. d. Most carbonates when heated,
decompose to form oxides and CO2.
Example: CaCO3 → CaO + CO2
The group IA carbonates do not decompose
readily.
e. Most hydrogen carbonates
(bicarbonates), when heated decompose
to form an oxide plus water and CO2.
Example: Ca(HCO3) → CaO = 2CO2 + H2O

19. When hydrogen carbonates of the Group IA
metals are heated they form a carbonate
plus water and CO2.
Example: 2NaHCO3 → Na2CO3 + CO2 + H2O

20. Substitution or Replacement reaction
is a type of reaction in which a metal
replaces another metal ion from a solution
or a nonmetal replaces a less active
nonmetal in a compound.

21. Activity series
used to predict the products of
replacement reaction. In using this
series, any free metal that is higher on
the list will displace from a solution
another metal that is lower. Hydrogen is
included in the series although it is not a
metal. Any metal above hydrogen in the
series will displace hydrogen gas from
an acid.

22. The activity series is used to predict the products of replacement
reaction.

25. Double Decomposition
a type of reaction wherein two compounds
react to form two new compounds. This
involves exchange of ion pairs.
Examples:
AgNO3 + HCI → AgCl +HNO3
Ba(NO3)2 + 2NaOH → Ba (OH)2 + 2NaNO3

27. References:
• http://chemistry.about.com/od/chemicalreactio
• http://www.wisegeek.org/what-are-chemical-re