Whether
A chemical reaction has taken place –
change in state
change in colour
evolution of a gas
change in
temperature.
Law
of conservation-masscan neither be created nor destroyed in a chemical
reaction. That is, the
Total
mass of the elements present in the products of a chemical reactionhas to be
equal to the total mass of the elements present in the reactants.in other
words, the number of atoms of each element remains the same, before and after a
chemical reaction.
During a chemical
reaction atoms of one element do not change into those of another element. Nor
do atoms disappear from the mixture or appear from elsewhere. Actually,
chemical reactions involve the breaking and making of bonds between atoms to produce
new substances.
Examples of
combination reactions-
Calcium oxide and
water combine to form a single product, calcium hydroxide
Burning of coal
Formation of water
from h2(g) and o2(g)
When two or more
substances (elements or compounds) combine to form a single product, the
reactions
Are called
combination reactions.
Reactions in which
heat is released along with the formation of products are called exothermic
Chemical reactions.
Example of exothermic reactions is – burning of natural gas, respiration, the
decomposition of vegetable matter into compost
When a single
reactant breaks down to give simpler products, then it is a decomposition
reaction
Calcium oxide is
called lime or quick lime
Decomposition reactions
require energy either in the form of heat, light or electricity for breaking
down the reactants. Reactions in which energy is absorbed are known as
endothermic reactions.
Such reactions in
which there is an exchange of ions between the reactants are called double
displacement
Reactions.
If a substance
gains oxygen during a reaction, it is said to be oxidised. If a substance loses
oxygen during a reaction, it is said to be reduced.
One reactant gets
oxidised while the other gets reduced during a reaction. Such reactions are
called oxidation-reduction reactions or redox reactions.
If a substance
gains oxygen or loses hydrogen during a reaction, it is oxidised. If a
substance loses oxygen or gains hydrogen during a reaction, it is reduced.
Usually substances
which prevent oxidation (antioxidants) are added to foods containing fats and
oil. Keeping food in air tight containers helps to slow down oxidation. Chips manufacturers
usually flush bags of chips with gas such as nitrogen to prevent the chips from
getting oxidised
Precipitation
reactions produce insoluble salts.
Next Topic:-Science Class 10 NCERT Textbook- Lesson-2
Next Topic:-Science Class 10 NCERT Textbook- Lesson-2
