Laws of chemical combination-
Law of conservation of mass....
In all physical and chemical changes,the total mass of the reactants in equal to that of the products.
Or,
Mass can neither be created nor destroyed.
This is also called as the law of indestructibility of matter.
The mass and energy are intercountable but the total sum of the mass and energy during any physical or chemical changes the names constant.
2Na +Cl2 = 2NaCl
Law of constant composition or definite proportions....
This law was discovered by a French chemist
J.L Proust .
It's state that,
A chemical compound is always found to be made up the same elements combined together in same fixed proportion by mass.
Example- A pure water obtained from whatever source or any country will always be made up of only hydrogen and oxygen elements combined together in the same fixed ratio of 1:8 by mass.
A sample of carbon dioxide maybe prepared in the laboratory.
a.heating limestone
b.by burning coal in air
c.by the action of dilute hydrochloric acid on marbel.
d.by heating sodium carbonate it is found that carbon dioxide is made up of same elements i.e
Carbon and oxygen combined together in the same fixed ratio of 3:8 by mass.
Limitations-
Its not applicable it an element exist in different isotopes which maybe involved in the formation of compounds.
The elements may combine in same ratio but the compounds formed maybe different.
Laws of multiple proportion -
When elements combine to form two or more chemical compounds then the masses of one of the elements which combined with a fixed mass of the other, bear a simple ratio to one other.
Example-
compound of carbon and oxygen:
Carbon combined with oxygen to form two compound namely carbon dioxide and carbon monoxide.
In carbon dioxide,12 parts by mass of carbon combined with 32 parts by mass of oxygen while in carbon monoxide,12 parts by mass of carbon combine with 16 parts by mass of oxygen.
The masses of Oxygen which combined with a fixed mass of carbon in carbon monoxide and carbon dioxide are 16 and 32 . These masses of oxygen bear a simple ratio of 16:32 or 1:2 to each other.
Ex- compound of sulphur
and oxygen:
The element sulphur also from two oxides sulphur dioxide and sulphur trioxide.
In sulphur dioxide,32 parts by mass of sulphur combine with 32 parts by mass of oxygen but in sulphur trioxide 32 parts by mass of sulphur combined with 48 parts by mass of oxygen . The masses of oxygen which combined with the fixed mass of sulphur in the two oxides are 32 & 48 .these bear a simple ratio of 32 :48 or 2:3 to each other.
Laws of reciprocal propertion-
It states thc cat-
The ratio of masses of 2 elements.A and B which combines separately with a fixed mass of the third element C is either the same or some multiple of the ratio of the masses in which A and B combine directly with each other.
Example- The elements carbon and oxygen combine separately with the third element hydrogen to from methane and water and they combine directly with each other to from carbon dioxide.
In methane 12 parts by mass of carbon combine with 4 parts by mass of hydrogen.in water,2 parts by mass of hydrogen combine with 16 parts by mass of oxygen.
Gay lussac's law of gaseous volume-
When gases react together they always do so in volumes which bear simple ratio to one another and to the volume of the products,if these are also gases, provided all measurements of volumes are done under similar conditions of tumperature and pressure and pressure.
Example-1)combination between hydrogen and chlorine:
1 volume of hydrogen and 1 volume of chlorine always combine to form two volumes of hydrochloric acid gas .
The ratio between the volumes of the reactants and the product. In this reaction is simple i.e
1:2:2
2) combined between nitrogen and hydrogen:
One volume of Nitrogen always combines with 3 volume of hydrogen to form 2 volumes of ammonia. This reaction also indicate a simple ratio of 1:3:2 between the volume of the reactants and products.
Dalton's atomic theory-
John Dalton in 1808 put forward theory know as Dalton's atomic theory.
Main point:
1. Matter is made up of extremely small indivisible particles called atoms
2.Atom of the same elements are identical in all respect i.e. shape,size and mass.
3. Atoms of different elements have different masses,size,and also possess different chemical properties
4. Atoms of different elements combined together to form molecules.
5. When atoms combine with one another to form molecules they do so in simple.
6. Atoms of two elements may combine in different ratio to form more than one compound.
7. An atom is the smaller particles that take part in a chemical reaction.
8. An atoms can neither be created nor destroyed.
Limitations..
1. It could explain the law of chemical combustion by mass but failed to explain the law of gaseous volume.
2. It could not explain why atoms of different elements have different elements have different masses,size valencies.
3. It could not explain. The Nature of binding forces between atoms and molecules which is count for the existence three states of matter.
Modern atomic theory-
1. Atoms is no longer considered to be indivisible:
It is made up of electron,protons and neutrons.
2. Atoms of the same element may have different atomic masses:
Atoms of the same elements which possess different atomic masses are called isotopes.
Example-1.Isotops of hydrogen..
1 2 3
H , H , H
1 1 1
2.Isotop of carbon...
14 12 13
C , C , C
3.Atoms of different elements may have same masses :
Atoms of different elements which have the same atomic masses are called isobars.
Example-calcium and argon have atomic number as 20 and 18 .
4. The ratio in which the different atoms combine with one another may be fixed and integral but maybe fixed and integral but may not be simple.
Example-In sugarcane the ratio in which the elements carbon, hydrogen and oxygen combined together 12:22:11 which is not simple.
5. Atom is the smallest particles that take part in a chemical reaction .
6. Atom is no longer indestructible :
By carring out nuclear reaction atom of an element may be changed into another.
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"some basic concepts of chemistry"
Thanks bro.
ReplyDeleteI'm a student of 11th
Your notes are really very good.
Thanks sir Nice notes
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