Chemical equations and their types

BY: VEENU GUPTA
by MS VEENU GUPTA ( CHEM) 6/5/2020

 The symbolic representation of a
chemical reaction is called a chemical
equation.
 It is also called as representation of
chemical reaction by means of symbols
of substances in the form of formulae.

 Example: A + B → C + D
 The reactants are written on the left hand side with
a plus sign between them.
 The products are written on the right hand side
with a plus sign between them.
 An arrow separates the reactants from the
products. The arrow head points towards the
products and indicates the direction of the reaction.
 Condition, if any, is written generally above the
arrow

 When hydrogen reacts with oxygen, it gives water. This
reaction can be represented by the following chemical
equation:
i) Hydrogen + Oxygen → Water
ii) H2 + O2 → H2O
In the first equation, words are used and in second,
symbols of substances are used to write the chemical
equation.
 For convenience, the symbol of substance is used to
represent chemical equations.
 A chemical equation is a way to represent the chemical
reaction in a concise and informative way.

 ATOMIC EQUATION
 MOLECULAR EQUATION
 SKELETAL EQUATION/UNBALANCED
CHEMICAL EQUATION.
 BALANCED CHEMICAL EQUATION AND

 It is a balanced chemical equation in which one or
more substances taking part in the reaction are
present in their atomic form.
 Na + H2O → NaOH + H(ATOMIC FORM)

 “IT IS A BALANCED CHEMICAL EQUATION IN WHICH
ALL THE SUBSTANCES TAKING PART IN THE
REACTIONS ARE PRESENT IN THEIR MOLECULAR
FORM.”
 2H2 + O2 →2H20
 H2 +Cl2 → 2HCl

 A chemical equation which simply represents
the symbols and formulas of reactants and
products taking part in the reaction is known
as skeletal chemical equation for a reaction.
 For example:
For the burning of Magnesium in the air,
Mg + O2 → MgO -is the skeletal equation.

(a)Hydrogen gas combines with nitrogen to form ammonia.
Ans. (a) H2 +N2 → NH3
(b) Hydrogen sulphide gas burns in air to give water and Sulpher
dioxide.
Ans (b) H2S + O2 → H2O + SO2
(c) Barium chloride reacts with aluminum sulphate to give
aluminum chloride and precipitate of barium sulphate
Ans (c) BaCl2 + Al2(SO4)3 → AlCl3 +BaSO4
(b) Zinc carbonate (s) Zinc oxide (s) + Carbon dioxide (g)
Ans (b) ZnO3 (s) → ZnO (s) + CO2 (g)
(c) Hydrogen (g) + Chlorine (g) Hydrogen chloride (g)
Ans (c) H2 (g) + Cl2 (g) → 2HCl

 If the number of atoms of each element in reactants is not
equal to the number of atoms of each element present in
the product, then the chemical equation is called
Unbalanced Chemical Equation.
Example: Fe + H2O → Fe3O4 + H2
 In this example, a number of atoms of elements are not
equal on two sides of the reaction.
 For example; on the left-hand side only one iron atom is
present, while three iron atoms are present on the right-
hand side. Therefore, it is an unbalanced chemical equation.

 A balanced equation is a chemical equation in which
number of atoms of each element is equal on both sides
of the equation i.e
number of atoms of an element on reactant side =
number of atoms of that element on the product side.
 Example: Zn + H2SO4 → ZnSO4 + H2
 In this equation, numbers of zinc, hydrogen and
sulphate are equal on both sides, so it is a Balanced
Chemical Equation.

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(b) Zn + 2AgNO3 →Zn(NO3)2 +2Ag
(c) Aluminum + Copper chloride → Aluminum chloride +Copper
(c) 2Al + 3Cl2 →2AlCl3 + 3Cu
(d) Barium chloride +Potassium sulphate →Barium sulphate + potassium chloride
(d) BaCl2 + K2SO4 →BaSO4 + 2KCl
(e) Hydrogen gas combines with nitrogen to form ammonia.
(e) 3H2 +N2 2NH3
(f) Hydrogen sulphide gas burns in air to give water and Sulpher dioxide
(f)2H2S + 3O2 2H2O + 2SO2

 Chemical equations needs to be balanced to justify
the law of conservation of mass.
 This law states that mass can neither be created nor
be destroyed during a chemical change or reaction ie
the total mass of the product must be equal to the
total mass of the reactant.

 The process of equating the number of
atoms on both the sides of a chemical
equation is known as balancing of a
chemical equation.

 Write the number of atoms of each element present
on the left hand side and right hand side.
 Always start balancing with the compound that
contains maximum number of atoms. It can be
reactant or a product. Then in that compound select
the element which has the maximum number of
atoms.
 While balancing a chemical equation, the molecular
formulas of the reactants and products should not
change. The molecular formulas are simply multiplied
by suitable coefficients.

 To make a chemical equation more informative,
the reaction conditions such as temperature,
pressure or catalyst are written on the arrow
separating the reactants and products.
 The evolution of gas is indicated by an upward
arrow.
 The formation of precipitate is indicated by a
downward arrow.
 Heat evolved during the reaction is written as +
Heat on the product side.
 Heat absorbed during the reaction is written as +
Heat on the reactant side.

Fe + H2O → Fe3O4 + H2
 Write the number of atoms of elements present in reactants and in products in a
table as shown here.
 Balance the atom which is maximum in number on either side of a chemical
equation. In this equation, the number of oxygen atom is the maximum on the
RHS.
 To balance the oxygen, one needs to multiply the oxygen on the LHS by 4, so
that, the number of oxygen atoms becomes equal on both sides.
Fe + 4 H2O → Fe3O4 + H2
Name of atom No. of atoms in the
reactant
No. of atoms in the
product
Iron 1 3
Hydrogen 2 2
Oxygen 1 4

 Now, the number of hydrogen atoms becomes 8 on the LHS, which is
more than that on the RHS. To balance it, one needs to multiply the
hydrogen on the RHS by 4.
Fe + 4 H2O → Fe3O4 + 4 H2
 After that, the number of oxygen and hydrogen atoms becomes equal
on both sides. The number of iron is one on the LHS, while it is three
on the RHS. To balance it, multiply the iron on the LHS by 3.
3 Fe + 4 H2O → Fe3O4 + 4 H2
 Now the number of atoms of each element becomes equal on both
sides. Thus, this equation becomes a balanced equation.
 After balancing, the above equation can be written as follows:
3Fe + 4H2O → Fe3O4 + 4H2.
Name of atom No. of atoms in the
reactant
No. of atoms in the
product
Iron 3 3
Hydrogen 8 8
Oxygen 4 4

EXAMPLES OF BALANCED
CHEMICAL EQUATIONS

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(a) Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(b) Zn + 2AgNO3 →Zn(NO3)2 +2Ag
(c) Aluminum + Copper chloride → Aluminum chloride +Copper
(c) 2Al + 3Cl2 →2AlCl3 + 3Cu
(d) Barium chloride +Potassium sulphate →Barium sulphate + potassium chloride
(d) BaCl2 + K2SO4 →BaSO4 + 2KCl
(e) Potassium bromide (s) +Barium iodide (aq) →Potassium iodide (aq) + Barium
bromide(s)
(e) 2KBr (aq) + BaI2 ( aq) → 2KI (aq) + Br2
(f) Zinc carbonate (s)+ heat → Zinc oxide (s) + Carbon dioxide (g)
(f) ZnO3 (s) → ZnO (s) + CO2 (g)

(g) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(g) H2 (g) + Cl2 (g) → 2HCl
(h) Magnesium (s) + Hydrochloric acid (aq) →Magnesium chloride
(aq) + Hydrogen (g)
(h) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
(i) Hydrogen + Chlorine → Hydrogen chloride
(i) H2 + Cl2 → 2HCl.
(j) Barium chloride +Aluminium sulphate →Barium sulphate+
Aluminium chloride
(j) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3.
(k)Sodium + water → Sodium hydroxide + water
(k) 2Na + 2H2O → 2NaOH + H2.

 Writing the symbols of physical states of substances in a chemical
equation
 By writing the physical states of substances, a chemical equation
becomes more informative.
 Gaseous state is represented by symbol (g).
 Liquid state is represented by symbol (l).
 Solid state is written by symbol (s).
 Aqueous solution is written by symbol (aq).
 Writing the condition in which reaction takes place: The condition is
generally written above and/or below the arrow of a chemical
equation.
 Thus, by writing the symbols of the physical state of substances and
condition under which reaction takes place, a chemical equation can
be made more informative.

 HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
 NaOH + H2SO4 → Na2SO4 + H2O
 NaCl + AgNO3 → AgCl + NaNO3
 BaCl2 + H2SO4 → BaSO4 + HCl

 Ans: (a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
 (b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
 (c) NaCl + AgNO3 → AgCl + NaNO3
 (d) BaCl2 + H2SO4 → BaSO4 + 2HCl

THANKS

Chemical equations and their types

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