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