# Basic Concepts of Chemistry

** Law
of Definite Proportion:** We know that mass is
conserved. If we were to take a sample of a

**pure compound**it will always contain the

**same elements**combined in the

**same proportion**by mass.

** Law
of Multiple Proportion:** If one element can combine
with another to form more than one compound then the

**mass ratios**of the elements in the compounds are

**simple**

**whole-number ratios**of each other.

** Law
of Definite Proportion by Volume:** The volumes of

**reactants and products**, in chemical reactions, are related to each other by

**simple whole-numbers**. Of course the measurements must be taken at the same temperature and pressure.

** Law
of Reciprocal Proportions:** The ratio by mass, in which
two elements combine with the

**fixed mass**of a third element, is either the

**same or a simple multiple**of the ratio in which they combine with each other.

__Avogardo’s
Law:__**Equal volumes** of all gases
contain **equal number of molecules** under
similar conditions of temperature and pressure.

** One
Atomic Mass Unit (amu):** It is a mass unit equal to
exactly one twelfth the mass of a carbon 12 atom.

** Formula
Mass of a Substance:** It is the

**sum of the atomic masses**of all atoms in a formula unit of a compound.

** Molar
Mass:** The mass of 1 mole of any substance.

__Molar Volume __**(V**_{m}**)****:** The volume of 1 mole of the
substance.

__Mole
(m):__

It is a number which is equal to

**6.023 x 10**^{23}It is the amount of substance which contains as many entities (atoms, molecules, ions or other particles) as there are

**atoms in exactly 12 grams**of Carbon 12 isotope.It is also known as

**Avogadro’s Constant**.

__Number
of Mole Method:__

Number of moles of a substance n = w (in gms)/m

also n = volume (in lt) at NTP/22.4lt

also n = M x vol in lt (where M is Molarity = number of moles of solute per lt of solution)

M=
(w/m) x (1000/ V_{m} )

Number
of mole method is used only in the case of **balanced
chemical equations**.

The
coefficients of balanced equations represent the ratios
in terms of **number of moles** in which the
reactants react or products are formed.

Number
of particles(ions, atoms or molecules) in a given number
of moles = number of moles x 6.023 x 10^{23} .

** Equivalent
Weight of an Element (E):** It is defined as the number
of parts by weight of the element which combine with or
displace from a compund 1 part by weight of Hydrogen, 8
parts by weight of Oxygen or 35.5 parts by weight of
Chlorine.

E = M
( Molar Mass) / n_{f} (n factor)

where:

n_{f}
= Valency in case of an atom

= Total positive or negative oxidation number of an atom in a molecule

= Basicity or Acidity.

= Change in oxidation number in case of a redox reacton.

__Number
of Gram Equivalents:__

= weight in gms / E (Equivalent wt)

= Normality x vol in lt

Normality
= (w/E) x (1000/V_{m}_{ })

** Number
of Equivalents Method:** In this method you need not
balance the chemical equation. The basic principle is
that the equivalents of each reactant which have
dissapeared are equal to the number of equivalents of
each of the products formed. The working tool for this is
equivalent weight.

Number
of equivalents = W in gms / Eq Wt = (W x n_{f} )
/ M

__Dulong
and Petit’s Law:__

Atomic wt (approx) = 6.4/specific heat(in calories)