Molecular Weight and Concept of Mole

Atomic weight:

The sum total of the number of protons and neutrons present in the nucleus of an atom is called atomic weight.

Molecular weight: The sum total of the atomic weights of various atoms present in a substance is called molecular weight. For example:

Molecular weight of CaCO₃ = ( 40 + 12 + 16×3)
= (40 + 12+ 48)
= 100

Similarly,
Molecular weight of water = H₂O
= (1×2 + 16)
= 18

Gram Molecular weight:

The molecular weight of a substance which is expressed in terms of gram is called gram molecular weight. For example:

The gram molecular weight of CaCO₃ is 100 gm.

Avogrado Number:

Each mole of any substance contains 6.023 x 10²³ particles or ions or atoms or molecules and this number is called Avogrado number.

Mole:

The collection of 6.023 x 10²³ particles or ions or atoms of a substance is called its one mole. Mole is equal to the gram molecular weight of a substance. For example:

Gram molecular weight of CaCO₃ = 100 gm.
1 mole of CaCO₃ = 100 gm.
100 gram of CaCO₃ = 6.023 x 10²³ particles

Rate of reaction:

It is defined as the change in concentration of any one of the reactants or products per unit time to complete the reaction.

Factors affecting rate of reaction:

1. In general, increase in temperature increases the rate of almost all chemical reaction while decrease in temperature decreases the reaction rate.
2. The rate of reaction increases with increase in the concentration of reactants.
3. The rate of reaction also depends upon the nature of the atom.