CHAPTER – 1
Chemical Reactionsand Equations
q Chemical Reaction : – Whenever a chemical change occurs we can say that
a chemical reaction has taken place
eg – Food gets digested in our body
– Rusting of iron.
q Chemical Equation :– A chemical reaction can be expressed symbolically
by using chemical equation
eg magnesium is burnt into air to form magnesium oxide can be represented
as
Mg + O2 → MgO
– We can observe or recognise a chemical reaction by observing change
in state, colour, by evolution of gas or by change in temperature.
q Physical state of the reactant and products are mentioned to make chemical
reaction more informative. eg we use (g) for gas, (l) for liquid, (s) for solid
and (aq) for aqueous.
q Balancing Equation :– We balance the chemical equation so that no. of
atoms of each element involved in the reaction remain same at the reactant
and product side.
eg Fe + H2O → Fe2O3 + H2 can be written as
3 Fe(s) + 4H2O(g) → Fe2O3(s) +4H2(g)
q Combination Reaction :– The reaction in which two or more substances
combine to form a new single substance
3 X – Science
AK
, eg CaO(s) + H2O(l)
→ Ca(OH)2 (aq)
Calcium Water Calcium hydroxide
oxide (slaked lime)
Quick lime
– Ca(OH)2 slaked lime is used for white washing walls. It reacts will CO2 to
form CaCO3 and gives a shiny finish to the walls.
Ca(OH)2 CO2
→ CaCO3 H2O (l)
(aq)+ (g) (s)+
Calcium Calcium
hydroxide Carbonate
– Burning of Coal
C(s) + O2(g) → CO2(g) + heat + light
– Formation of water
2H2(g) + O2(g) → 2H2O(l)
q Exothermic Reactions :– Reaction in which heat is released along with the
formation of products.
eg. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
– Respiration is also exothermic reaction.
– De composition of vegetable matter into compost.
q De compositon Reactions :– The reaction in which a single substance
decomposes to give two or more substances. De composition reactions can
be of three types
Thermal Decompositon :– When a decompositon reaction is carried out by
heating
4 X – Science
AK
Chemical Reactionsand Equations
q Chemical Reaction : – Whenever a chemical change occurs we can say that
a chemical reaction has taken place
eg – Food gets digested in our body
– Rusting of iron.
q Chemical Equation :– A chemical reaction can be expressed symbolically
by using chemical equation
eg magnesium is burnt into air to form magnesium oxide can be represented
as
Mg + O2 → MgO
– We can observe or recognise a chemical reaction by observing change
in state, colour, by evolution of gas or by change in temperature.
q Physical state of the reactant and products are mentioned to make chemical
reaction more informative. eg we use (g) for gas, (l) for liquid, (s) for solid
and (aq) for aqueous.
q Balancing Equation :– We balance the chemical equation so that no. of
atoms of each element involved in the reaction remain same at the reactant
and product side.
eg Fe + H2O → Fe2O3 + H2 can be written as
3 Fe(s) + 4H2O(g) → Fe2O3(s) +4H2(g)
q Combination Reaction :– The reaction in which two or more substances
combine to form a new single substance
3 X – Science
AK
, eg CaO(s) + H2O(l)
→ Ca(OH)2 (aq)
Calcium Water Calcium hydroxide
oxide (slaked lime)
Quick lime
– Ca(OH)2 slaked lime is used for white washing walls. It reacts will CO2 to
form CaCO3 and gives a shiny finish to the walls.
Ca(OH)2 CO2
→ CaCO3 H2O (l)
(aq)+ (g) (s)+
Calcium Calcium
hydroxide Carbonate
– Burning of Coal
C(s) + O2(g) → CO2(g) + heat + light
– Formation of water
2H2(g) + O2(g) → 2H2O(l)
q Exothermic Reactions :– Reaction in which heat is released along with the
formation of products.
eg. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
– Respiration is also exothermic reaction.
– De composition of vegetable matter into compost.
q De compositon Reactions :– The reaction in which a single substance
decomposes to give two or more substances. De composition reactions can
be of three types
Thermal Decompositon :– When a decompositon reaction is carried out by
heating
4 X – Science
AK
