Chemical Reactions and Equations
Introduction to Chemical Reactions and Equations
Physical and chemical changes
Chemical change - one or more new substances with new physical and chemical properties
are formed.
Example: F e(s) + CuSO (aq) → F eSO (aq) + Cu(s)
4 4
(Blue) (Green)
Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and
copper are formed.
Physical change - change in colour or state occurs but no new substance is formed.
Example: Water changes to steam on boiling but no new substance is formed(Even though
steam and water look different when they are made to react with a piece of Na, they react
the same way and give the exact same products). This involves only change in state (liquid
to vapour).
Observations that help determine a chemical reaction
A chemical reaction can be determined with the help of any of the following observations:
a) Evolution of a gas
b) Change in temperature
c) Formation of a precipitate
d) Change in colour
e) Change of state
Chemical reaction
Chemical reactions are chemical changes in which reactants transform into products by
making or breaking of bonds(or both) between different atoms.
Types of chemical reactions
, Taking into consideration different factors, chemical reactions are grouped into multiple
categories.
Few examples are:
● Combination
● Decomposition
● Single Displacement
● Double displacement
● Redox
● Endothermic
● Exothermic
● Precipitation
● Neutralisation
Chemical Reactions and Equations I
Word equation
A word equation is a chemical reaction expressed in words rather than chemical
formulas. It helps identify the reactants and products in a chemical reaction.
For example,
Sodium + Chlorine → Sodium chloride
The above equation means: "Sodium reacts with chlorine to form sodium chloride."
Symbols of elements and their valencies
A symbol is the chemical code for an element. Each element has one or two letter atomic
symbol, which is the abbreviated form of its name.
Valency is the combining capacity of an element. It can be considered as the number of
electrons lost, gain or shared by an atom when it combines with another atom to form a
molecule.
Writing chemical equations
Representation of a chemical reaction in terms of symbols and chemical formulae of the
reactants and products is known as a chemical equation.
Zn(s) + dil. H2 SO4 (aq) → ZnSO4 (aq) + H2 (↑)
(Reactants) (Products)
• For solids, the symbol is "(s)".
• For liquids, it is "(l)".
• For gases, it is "(g)".
Introduction to Chemical Reactions and Equations
Physical and chemical changes
Chemical change - one or more new substances with new physical and chemical properties
are formed.
Example: F e(s) + CuSO (aq) → F eSO (aq) + Cu(s)
4 4
(Blue) (Green)
Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and
copper are formed.
Physical change - change in colour or state occurs but no new substance is formed.
Example: Water changes to steam on boiling but no new substance is formed(Even though
steam and water look different when they are made to react with a piece of Na, they react
the same way and give the exact same products). This involves only change in state (liquid
to vapour).
Observations that help determine a chemical reaction
A chemical reaction can be determined with the help of any of the following observations:
a) Evolution of a gas
b) Change in temperature
c) Formation of a precipitate
d) Change in colour
e) Change of state
Chemical reaction
Chemical reactions are chemical changes in which reactants transform into products by
making or breaking of bonds(or both) between different atoms.
Types of chemical reactions
, Taking into consideration different factors, chemical reactions are grouped into multiple
categories.
Few examples are:
● Combination
● Decomposition
● Single Displacement
● Double displacement
● Redox
● Endothermic
● Exothermic
● Precipitation
● Neutralisation
Chemical Reactions and Equations I
Word equation
A word equation is a chemical reaction expressed in words rather than chemical
formulas. It helps identify the reactants and products in a chemical reaction.
For example,
Sodium + Chlorine → Sodium chloride
The above equation means: "Sodium reacts with chlorine to form sodium chloride."
Symbols of elements and their valencies
A symbol is the chemical code for an element. Each element has one or two letter atomic
symbol, which is the abbreviated form of its name.
Valency is the combining capacity of an element. It can be considered as the number of
electrons lost, gain or shared by an atom when it combines with another atom to form a
molecule.
Writing chemical equations
Representation of a chemical reaction in terms of symbols and chemical formulae of the
reactants and products is known as a chemical equation.
Zn(s) + dil. H2 SO4 (aq) → ZnSO4 (aq) + H2 (↑)
(Reactants) (Products)
• For solids, the symbol is "(s)".
• For liquids, it is "(l)".
• For gases, it is "(g)".
