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CHEMICAL REACTIONSAND
EQUATIONS
PROPERTIES OFA CHEMICAL
REACTION CHANGE IN STATE
CHANGE IN COLOUR EVOLUTION OF GAS
CHANGE IN TEMPRETURE
WHAT IS CHEMICAL EQUATION?A schematic representation of
any chemical reaction with the help of symbols and formulae of various species is called chemical equation
Example:Magnesium
+ 0xygen
Magnesium oxide
ESSENTIALS OF CHEMICAL EQUATIONS
IT SHOULD REPRESENT A TRUE CHEMICAL CHANGE
IT SHOULD BE BALANCED
IT SHOULD BE MOLECULAR
IT SHOULD REPRESENT THE CHANGE IN TEMPERATURE
BALANCING A CHEMICAL EQUATION Write the correct skeletal equation containing the
formulae of only one molecule of each reactant and product
Start with the compound that has the maximum atoms and the atoms present in it are balanced first.it may be a reactant or a product. Balance the element that appear only once on each side of the arrow first. Then balance the element which appear more than once
Elementary substance are balanced at the end. If required ,the whole equation is multiplied by some suitable no. In order to make all the coefficient whole no. but formulae can not be changed for balancing
CFor example : Reaction of calcium with water Skeletal equation calcium + water calcium hydroxide + hydrogen
Proper equation: Ca(s) + H2o(l) Ca(oh)2 + H2
Balance equations (By Hit and Trial method)
a) Count each kind of atom on both sides
b) The most complicated formulae in the above equation is Ca(OH)2 . The equation is balanced with respect to Ca, so we can balance ‘O’ by setting 2 just before h20.
Ca + 2H2O Ca(OH)2 + H2 Hence, hydrogen is balanced.
ATOM LHS RHS
Ca 1 1
O 1 2
H 2 4
C(c) Each kind of atom is counted on both the sides again which are now equal and therefore, the equations is balancedINFORMATION CONVEYED BY A CHEMICAL
EQUATION The names of the various reactant and
product The formulae of the reactant and product. The relative amount of the reactant and
product. The physical state of the reactant and the
product. Heat change during the reaction. The specific condition necessary for the
reaction
reactanTYPES OF CHEMICALREACTIONS
COMBINATION REACTION DECOMPOSITION REACTION DISPLACEMENT REACTION DOUBLE DECOMPOSITION DOUBLE DISPLACEMENT REACTION
COMBINATION REACTIONThe reaction in which two or more reactants combine to form a single product is known as a combination reaction.
+A B AB
Magnesium oxide
Watch glass
Burner
Mg ribbon
Tong
Example: Burning of
Magnesium in air2Mg + O2 2MgO + Heat
Quick lime that is Calcium Oxide when reacts vigorsly with water produces slacked lime
CaO(s) + H2O Ca(OH)2 (aq)
+ Heat
Beaker
Water
Calcium Oxide
Burning of coal
C(s) + O2(g) CO2 + Heat
DECOMPOSITION REACTIONIn such reaction , a single reactant breaks down to give simpler product
+
AB
B
A
Example : Lead Nitrate powder on heating decomposes to
give brown fumes of nitrogen dioxide with cracking sound
2Pb(NO3) 2PbO + 4NO2 + O2
Test tube holder
Boiling tube
Lead nitrate
Burner
TYPES OF DECOMPOSITION REACTION
There are three types of decomposition reaction :
ioTHERMAL DECOMPOSITION
When a decomposition reaction is carried out by hating , it is called thermal decomposition
2FeSO4
Fe2O3 + SO2 + SO3
PHOTOCHEMICAL DECOMPOSITIONIf the energy of the sunlight (in the form of photons) is used to carry out the decomposition reaction , then it is called photochemical decomposition
2AgCl 2Ag + Cl2
ioELECTROLYTIC DECOMPOSITIONIf electric current is used to carry out decomposition reaction, then it is called electrolytic decompositionExample : Electrolysis of water
It is the decomposition of water into oxygen and hydrogen when an electric current is passed through water containing few drops of dilute sulphuric acid2H2O 2H2 + O2
DISPLACEMENT REACTIONIn a displacement reaction , a more reactive element displaces a less reactive element from its compound (generally salt solution)
+ +less reactive element
More reactive element
Example :
Fe + CuSO4 FeSO4 + Cu
DOUBLE DECOMPOSITION/DOUBLE DISPLACEMENT REACTION
In this reaction , two compounds react by exchange of ions to form two new compound. In these reaction , generally precipitation occurs.
+ +
Example :
On mixing sodium sulphate(Na2SO4) solution with barium chloride(BaCl2) solution , a white precipitate of barium sulphate(BaSO4) is formed.Na2SO4 + BaCl2
BaSO4 + 2NaCl
AB CD
AC
BD
OOXIDATION AND REDUCTION Old concept
Oxidation: Addition of oxygen or electronegative element to a substance or removal of hydrogen or electropositive element from the substance is called oxidation
Reduction: Addition of electropositive element or hydrogen in an element or removal of oxygen or electronegative element from a substance is called reduction.
CuO + H2 Cu + H2O
Oxidation
Reduction
OModern concept:Oxidation: Loss of electrons from an element or increase in +ve electrovalency of an element is called oxidation.
Reduction: Gain of electron by an element (like Na,K,Mg) or removal of an electronegative elementRedox reaction: The reaction in which oxidation and reduction takes place simultaneously are known as redox reaction.
EFFECT OF OXIDATION IN EVERY DAY LIFE
Corrosion: The slow eating up of metals by the action of air, moisture or a chemical on their surface is called corrosion.(1) Iron articles get coated with a reddish brown powder when left open in moist air for a long time . This process is commonly known as rusting of iron2Fe + 3/2O2 + XH2O
Fe2O3 . XH2O ; where X = No. of water molecules
Rancidity: Food material containing fat or oil when left for a long time become rancid i.e. smell and taste changes. This is because they get oxidised when they came in contact with the atmospheric oxygen. This is called rancidity
Some other reaction…….
Polymerization reaction
The process in which a large number of simple small molecules (monomers) are combined together to form very large molecule (polymer) is termed as polymerisation.
nA
polymerization (A) n
monomer
polymer
Example:
nCH2 = CH2Ethene
( CH2 – CH2 )Polyethene
polymerization
eaction
Precipitation reaction
The reaction in which an insoluble substance formed is called as a precipitation reaction and the insoluble substance is called as precipitateExample:
NaCl + AgNO3 NaNO3 + AgClsodiumchloride
Silver nitrate
Sodium nitrate
Silver chloride
……A CHEMISTRY POWER POINT PRESENTATION
Thank you