Studied by 16 people
physical change
the change in which only the change in colour, shape and state takes place and no new substance is formed. usually physical changes are reversible
chemical change
the change in which one or two compounds are combined chemically to form a new substance. most of the chemical changes are irreversible
reactant
the substances which are on the [LHS] and take part in the chemical reactions
product
the substances which are on the [RHS] and are formed during a chemical reaction
the law that governs chemical reaction
the law of conservation of mass-
mass of the reactant is always equal to the mass of the product.
during a chemical reaction mass can neither be created nor be destroyed
observations that determine a chemical reaction
evolution of gas
formation of precipitate [insoluble solid formed during a chemical reaction]
change in temp
change in colour
change in state
change in state
mg[s] + o2[g] = mgo2[s]
2H2 +O2 = 2H2O
change in colour
the reaction of heat on green viterol= feso4 . 7H2O [green] + heat = feso4 [colourless] + 7H2O
and when we heat it further
2feso4 + heat = fe2O3 [reddish brown]+ SO2 +SO3
the reaction of heat on blue viterol= cuso4 .5H2O [blue] + heat = cuso4 [colourless] + 5H2O
change in temperature
there are two types of reactions
Exothermic reaction is when heat is liberated during a chemical reaction
Endothermic reaction is when heat is absorbed during a chemical reaction
endothermic reaction
the heating of calcium carbonate
CaCO3 + heat = CaO + CO2
the photosynthesis process is also an example of endothermic reactions as it uses CO2, H2O and sunlight the plant absorbs heat from the sunlight therefore we can say that it is an endothermic reaction
CO2 + H2O + heat = C6H12O6 + O2
note - all thermal decomposition reactions are endothermic in nature as they absorb heat to break down and form the product
exothermic reaction
the reaction of water on calcium oxide
CaO [quick lime] + H2O = Ca[OH]2 [slaked lime] + heat
every combustion reaction is an exothermic reaction
dilution of acids is also an exothermic reaction as it releases heat
evolution of gas
when gas is evolved during a chemical reaction.
AgCl = 2Ag + Cl2
formation of precipitate
an insoluble substance formed during a chemical reaction is called precipitate [ppt].
BaCl2 + Na2SO4 = BaSO4 [white ppt formed] + 2NaCl
types of chemical reactions
combination reaction
decomposition reaction -
thermal decomposition reaction
electrolytic decomposition reaction
photolytic decomposition reaction
single displacement reaction
double displacement reaction
redox reaction
combination reaction
when two or more reactants come together to form one single product
CaO + H2O = Ca[OH]2
decomposition reaction
when a single reactant is broken down into two or more products
there are three types of decomposition reaction
thermal decomposition - where the reactant is broken down by the application of heat ex- CaCO3 = CaO + CO2
electrolytic decomposition - where the reactant is broken down by the application of electricity ex- 2H2O = 2H2 + O2
photolytic decomposition - where the reactant is broken down by the application of sunlight ex- 2BaCl = Ba2 + Cl2
single displacement reaction
the reaction where a high a reactive element displaces with a low reactive element ex- Fe + CuSO4 = FeSO4 + Cu
double displacement reaction
the reaction where exchange of ions occur between two ionic compounds
NaCl + AgNO3 = NaNO3 + AgCl
BaCl + NaSO4 = BaSO4 + NaCl
generally in double displacement ppt is formed
redox reaction
the reaction where the process of oxidation and reduction take place simultaneously
combination reaction and single displacement reaction are redox reactions
oxidation
there are 2 concepts of oxidation
classical concept - 1. addition of oxygen is called as oxidation
2. the process of removal of hydrogen is known as reduction
electronic concept - 1. loss of electron is known as oxidation
2. increase in +ve charge is known as oxidation
reduction
there are 2 concepts of reduction
classical concept - 1. removal of oxygen from a compound is known as reduction
the process of addition of hydrogen is known as reduction
electronic concept - 1. gain of electron is known as reduction
the increase in -ve charge is known as reduction
if oxidation and reduction are so opposite then how do they work together?
if we want to give electron so we should have someone to accept it and this is what happens between reduction and oxidation
oxidising agent
the compound which itself undergoes the process of reduction but oxidises the other compound is an oxidising agent
reducing agent
the compound which itself undergoes the process of oxidation but reduces the other compound is a reducing agent
some of the redox reactions
ZnO + Cu = Zn + CuO in this reaction ZnO is the oxidising agent and Cu is the reducing agent
CuO + H2 = Cu + H2O in this reaction CuO is the oxidising agent and H2 is the reducing agent
CuO + C = Cu + CO in this reaction CuO is the oxidising agent and C is the reducing agent
Corrosion
it is the process by which a metal surface is attacked by a substance such as air or water. In short it is the oxidation of metal
methods for preventing corrosion
painting - a temporary way of increasing the life of a metal is by coating it with oil paints
Galvanising - deposition of zinc metal on the surface of the metal is called galvanising and this method is better than painting. the zinc sacrifices itself to protect the inner metal.
Using magnesium metal - magnesium sacrifices itself and prevents the corrosion of iron. underground pipes and ships are coated with magnesium.
Alloy formation - homogeneous mixture that is obtained by mixing two metals or non-metals is called an alloy. Alloy formation prevents rusting and increases the life of metal
corrosion of different metals
corrosion of iron is called rusting Fe2O3.XH2O
corrosion of copper is CuCO3.Cu[OH]2
corrosion of silver is also called tarnishing of silver Ag + H2S = Ag2S + H2
Rancidity
the process in which food containing oil and fat gets detoriated/degraded/spoiled due to oxidation reaction.
it causes change in taste,smell and decreases nutritional value of food
prevention of rancidity
we can prevent rancidity by flushing nitrogen gas in the bag of chips
addition of chemical materials called antioxidants of food such as BHT - butyalated hydroxytoulene and BHA - butyalated hydroxy anisole
Note
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