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Saturday, 26 September 2015

FSc Notes Chemistry Part 1 Chapter 1 Basic Concepts Lecture 3

FSc Notes Chemistry Part 1 Chapter 1 Basic Concepts

Thermodynamics:

The branch of science which deals with the study of transfer- motion of heat from a region of high temp. to a region of low temp is known as thermodynamics.
1st law of thermodynamics (law of conservation of energy):
this law states that “energy can nether be created nor destroyed, however it can be converted from one from to another”.

Concept of Mole & Avogadro no:

Mole:

The atomic mass of an element, molecular mass of a molecule or formula mass of a formula unit, expressed in grams, is called one mole of that element, molecule or formula unit, e.g Gram At. Mass of O= 16 g = 1 mole oxygen element.
N= 14 g= 1 mole of N element,
Na= 23g= 23g = 1 mole of Na element
H= 1g = 1 mole of H element

Similarly :
Gram Molecular mass of O =16 g = 1 mole oxygen element.
N = 14g = 1 mole of n element.
Na = 23 g = 1 mole of Na element.
H = 1g = 1 mole of H element.

Similarly:
Gram Molecular Mass of H2O = 18 g = 1 mole of H2O molecules
HCL = 36.5 g = 1 mole of HCL molecules.
O2 = 32g = 1 mole of O2 molecules

Similarly:
Gram formula Mass of NaCL = 58.5g = 1 mole of NaCL formula units.
MgO = 40 g = 1 mole of MgO formula units.

No of moles of a substance ( element, molecule or formula unit) is represented by “ n” & can be calculated by the following formulas.

Examples:
What is the no of moles (or gram atoms of 0.1 of g on Na.
No of moles of Na (n Na) = ?
Mass of Na (m Na) = 0.1 g
Solution:
n = Mass (g) of Na / At Mass of Na
n = 0.1/23
n = 0.0043 moles or 4.3*10-3

Avogadro No (NA):

As one dozen of eggs , one dozen of bananas and one dozen of oranges have fixed no. of items (eggs, bananas & oranges) although they have different masses, different fast and different nature , likewise it the case for one mole of a substance ( element, molecule or formula unit ).
So we can say that : one mole of any substance contains a fixed no of particles. This fixed no, is called Avogadro No. it is represented by “Na” and its value is 6.023*1023.
For example:
1 mole ( 23g) of Na element = 6.023*1023 Na atoms.
1 mole ( 1.008g ) of H element = 6.023*1023 H atoms.
1 mole ( 16g ) of oxygen element = 6.023*23 O atoms.

Similarly
1 mole ( 18g ) of H2O Molecule = 6.023* H2O Molecule.
1 mole ( 32 ) of O2 Molecule = 60023*1023 O2 Molecule.
1 mole ( 58.5g ) of NaCl formula unit.= 6.023*1023 NaCl formula units.
1 mole of Na+ = 6.023*1023 Na+ ions
1 mole of Cl-= 6.023*1023 Cl- ions.

Chemical Reaction:

The process in which two or more substances combine in such a way that the old bonds between their atoms are broken down and new bonds are formed to form new substances is known as chemical reaction.
For example when two moles of Hydrogen gas ( H2 ) combine with one mole of oxygen gas ( O2 ) the old bonds between the atoms of these two gas are broken down and these atoms form new bonds in such a way t form two moles of H2O molecules.
The substances which combine to undergo chemical reaction & whose bonds are broken are called the “Reactants” while the substances which are formed as a result of chemical reaction are known as products.

Chemical Equation:

The representation of a chemical reaction in terms of symbols and formulas of reactants and products is known as chemical equation.
Or
The symbolic representation of a chemical reaction is known as chemical equation.
e.g
2H2 + O2-------------------------- 2H2O
In a chemical equation, the reactants and the products are separated by means of an arrow. The reactants are at at he left side of the arrow while products are at the right side. The arrow is always directed from reactants to products.
I .e
Reactants -----------------Products.

Written by: Asad Hussain

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