This document discusses physical and chemical changes, providing definitions and examples of each. A physical change alters a substance's physical properties but not its chemical composition, and can be reversed. A chemical change produces new substances with different properties than the original, through rearrangement of atoms, and cannot be reversed. The document also discusses the importance of balanced chemical equations in showing reactants, products, and mole ratios in chemical reactions. Four main types of chemical reactions are defined: combination, decomposition, displacement, and double decomposition.

1. PHYSICAL AND CHEMICAL
CHANGES- CHEMICAL
EQUATIONS

2. INTRODUCTION
Physical Change Definition
 A physical change is a change in which no new substance is formed. The substance
may change in shape, size, and physical state and appearance, but not in its chemical
composition. Physical change may be a temporary (reversible) or permanent
(irreversible) change.
Chemical Change Definition
 A chemical change is a permanent change in which new substance(s) are formed. The
new substance(s) shows composition and properties which are completely different
from those of the original substance.

3. Physical Change Chemical Change
• Change is temporary • Change is permanent
• No new substance is formed. There is
change only in physical properties.
• New substances are formed with entirely
different physical and chemical properties.
• Change can be reversed by simple physical
methods.
• Change cannot be reversed by simple
physical methods.
• Energy may or may not be released or
absorbed.
• Energy is released or absorbed during
chemical change.
• Most of the time original form of the
substance can be obtained easily by simple
physical methods.
• The original substance cannot be obtained
by simple physical methods.
DIFFERENCE BETWEEN PHYSICALAND CHEMICAL CHANGE

4. The significance of a balanced chemical equation
A balanced chemical equation is a wonderful way of I representing a lot of information in a
concise manner.
1. It shows which substances are taking part in a I chemical reaction and what products are I
obtained as a result of it (Qualitative).
2. It shows both the number of molecules and the I number of atoms involved in the reaction.
3. It enables us to calculate the actual amount I (mass) of reactants and products involved in the I
reaction (Quantitative).
4. It makes the study of chemistry universally I standardized.
Example : 2Mg + 0a 2Mg0
This chemical equation indicates that :
i. magnesium reacts with oxygen to form I magnesium oxide.
ii. two monoatomic molecules of magnesium I combine with one diatomic molecule of I oxygen
to produce two molecules of I magnesium oxide.
iii. 48 amu of magnesium reacts with 32 amu of I oxygen to produce 80 amu of magnesium I
oxide.

5. TYPES OF CHEMICAL REACTION
1. Combination reaction
A combination reaction is a reaction where two or more elements or compounds combine
to form a single compound. Such reactions are represented by equations of the following
form: X + Y → XY. The combination of two or more elements to form one compound is
called a combination reaction.
2. Decomposition reaction
Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a
single chemical entity into two or more fragments. Chemical decomposition is usually
regarded and defined as the exact opposite of chemical synthesis.
2. Displacement reaction
A single-displacement reaction, also known as single replacement reaction or exchange
reaction, is a chemical reaction in which one element is replaced by another in a compound.
2. Double decomposition reaction
A double decomposition reaction is a type of decomposition reaction in which two
constituent reactants interchange positive and negative ions and form two new compounds.
Example : HCl(aq) + NaOH(aq) → NaCl(aq) + HOH(l)

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