Chemical Eequivalence

Significance of Equivalent WeightAn equivalent of a substance is defined as the amount o it which combines with 1 mole of hydrogen atoms or replaces the same number of hydrogen atoms in a chemical reaction. The weight in grams of 1 equivalent is called the equivalent weight in grams. For example, in the compounds HBr one mole of H combines with one mole of Br, 1/2 mole of O and 1/3 mole of N respectively. Hence the equivalent weights in grams of Br, O and N are the weights of 1 mole each of Br, O and N contains their 1 equivalent, 2 equivalents and 3 equivalents respectively.Thus : eq.wt. of Br= 1x79.9=79.9
To determine the equivalent weight of an element, it is not necessary to proceed from its hydrogen compound only. Eequivalent weight of an element can be calculated using the composition of the compound of the given element with any other element, whose equivalent weight is known by the knowledge of the Law of Equivalence. The law states that one equivalent of an element combines with one equivalent of the other. Accordingly, the equivalent weight of an element is the weight of its moloe combining with one equivalent of another element.The equivalent weight of a compound taking part in a reaction is the weight of the compound which combines with 1 equivalent of another compound. Thus knowing that 1 mole of HCl is equal to 1 equivalent of it, equivalent weight of Sodium carbonate can be calculated from the the equation. In an acid-base neutralisation reaction the equivalent weight of an acid is that portion of the weight of 1 mole of the acid which can furnish 1 mole of H, and the equivalent weight of a base is the portion of weight of one mole of the base which can furnish 1 mole of OH or accept 1 mole of H. In redox reactions, the equivalent weight of an oxidising or a reducing agent is the portion of the weight of 1 mole of substance that picks up or releases 1 mole of electrons respectively.

Molecular Weight

Molecular weight of a compound is defined as the weight of a molecule of the compound relative to a carbon atom, the atomic weight of which is supposed to be exactly 12. The molecular weight when expressed in grams is called gram molecular weight. The molecular weight in grams is, in fact, the weight of 1 mole of molecules, e.g., molecular weight of oxygen is 3 and 32 g is the weight of 1 mole of oxygen molecules. Mathematically,

molecular weight = weight of molecules in grams/number of moles of molecules

Molecular weight is measured in atomic mass unit (amu). Atomic mass unit is defined as 1/12 of the mass of the carbon isotope. There are various methods to determine the molecular weight of compounds viz,. vapour-density method. depression-in-freezing-point method, elevation-in-boiling-point method, gravimetric method, volumetric method, etc. The problems on molecular weight based on depression-in-freezing-point and elevation-in-boiling-point methods shall be discussed in Next blogs.
The mole method is found to be very useful in tackling the problems on molecular weight based on the aforesaid methods.

Some about Atomic weight

Atomic weight
The atomic weight of an element is defined as the average weight of the atoms of the element relative to a carbon atom, taken as exactly 12. Atomic weight in grams is, in fact, the weight of one mole of atoms, e.g., the atomic weight of oxygen is 16 and so 16 grams is the weight of 1 mole of oxygen atoms.
Mathematically,
atomic weight = weight of atoms in grams/number of moles of atoms
Atomic weight is measured in atomic mass unit. Atomic mass unit is defined as 1/12 of the mass of the C isotope. One amu is also called one dalton.

Gas Analysis

Gas Analysis
Gaseous reactions are carried out in a special type of tube known as an eudiometer tube. The tube is graduated in millimetres for volume measurement. The reacting gases taken in the eudiometer tube are exploded by sparks, produced by passing electricity through the platinum terminals provided in the tube. The volumes of the products of a gaseous explosion are determined by absorbing them in suitable reagents, e.g., Carbon dioxide and sulphur dioxide are absorbed in KOH solution, Oxygen is absorbed in a solution of alkaline pyrogallol, Water vapour produced during the reaction changes to liquid on cooling, the volume of water is neglected, but while applying POAC, moles of Water produced cannot be neglected.
Eudiometry is mainly based on Avogadro.s law, which states that equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules. Two gases having equal number of applied in solving the problems of this chapter, keeping in mind that in a gaseous reaction the relative volumes of each reactant and product represent their relative numbers of moles.

About Stoichiometry

STOICHIOMETRY
The word stoichiometry is derived from the Greek words stoicheion, which means element, and metrein, which means to measure. The numerals used to balance a chemical equaton are known as stoichiometric coefficients. These numbers are essential for solving problems based on chemical equations. Hece such problems are also called stoichiometric calculations.
For stoichiometric calculations, the mole relationships between different reactants and products are required, as from them, the mass-mass, mass-volume and volume-volume relationships between different reactants and products can be obtained.
Concept of Limiting Reagent
In single-reactions, the calculations are carried out wi only that amount of teh reactant which has converted to the product. This is done in all the methods mentioned above.
In the reactions where more than one reactant is involved, one has to first identify the limiting reactant, i.e., the reactant which is completely consumed. All calculations are to be carried out with the amount of the limiting reactant only. Now the questioni s how to identify the limiting reactant? The procedure is simple as illustrated below:
Initially.... 5 moles 12 moles 0 moles
A + 2B ----> 4C
If A is the limiting reactant : moles of C producec = 20
If B is the limiting reactant : moles of C produced = 24
The reactant producing the least number of moles of the product is the limiting reactant and hence A is the limiting reactant. Thus,
Initially .... 5 moles 12 moles 0 moles
A + B -------> 4C
Finally.... 0 moles 2 moles 20 moles
The limiting reactant can also be ascertained by knowing the initial number of equivalents of each reactant. The reactant with the least number of equivalents is the limiting reactant. The equivalent method to identify the limiting reactant can be applid even if the chemical equation is not balanced.

Mole Concept

Mole Concept
The mole concept is an essential tool for the study of the fundamentals of chemical calculations.
Mole in Latin means heap or mass or pile. A mole of atoms is a collection of atoms whose total weight is the number of grams equal to the atomic weight. As equal numbers of moles of different elements contain equal numbers of atoms, ti is convenient to express amounts of the elements of the elements in terms of moles. Just as a dozen means twelve objects, a score means twenty objects, chemists have defined a mole as a definite number of particles. This definite number is called the Avogadro constant, equal to 6.022 X 10 to the power 23, in honour of the concept of a mole without knowing the value of the Avogadro constant. Thus, a mole of hydrogen atoms or a mole of hydrogen molecules or a mole of hydrogen ions, or a mole of electrons means the Avogadro constant of hydrogen atoms, hydrogen molecules, hydrogen ions or electrons respectively.
The value of the Avogadro constant depends on the atomic-weight scale. The mole is defined as the amount of a substance containing as many atoms, molecules, ions, electrons or other elementary entities as there are carbon atoms in exactly 12 g of 12C.
In modern practice, a gram-molecule and a gram-atom are termed as a mole of molecules and a mole of atoms respectively,
Significance of Chemical Equations
A chemical equation describes the chemical process both qualitatively and quantitatively. The stoichiometric coefficients in the chemical equation give the quantitative information of the chemical process. These coefficients represent the relative number of molecules or moles of the reactants and products.
Principle of Atom Conservation
The principle of conservation of mass, expressed in the concepts o atomic theory, means the conservation of atoms. And if atoms are conserved, moles of atoms shall also be conserved. This is known as the principle of atom conservation. This principle is in fact the basis of the mole concept.
Advantages of the Mole Method over other Methods
The advantages of the Mole Method are as under:
1. Balancing of chemical equations is not required in the majority of problems as the method of balancing the chemical equation is based on the principle of atom conservation.
2.Number of reactions and their sequence, leading from reactants to products, need not be given.
3.It is a general method, applicable in solving many types of problems as may be seen in different chapters.

Intoduction of physical chemistry

Chemistry is just one of the subjects you have to study and, therefore, you have limited time for each subject. Keeping inmind your limited time and requirements.
Physical chemistry is a branch of chemiiiistry which deals with physical state of compounds, elements or substances. To learn Physical chemistry is very essential for all those students who intersted in chemistry and want to go in depth of chemistry.
Firstly we have to know that what is physical chemistry and why it is so useful for chemistry. Here are some useful topics of Physical chemistry which we have to must read during knowing about chemistry. Without Physical chemistry we can not learn good about chemistry.
In Physical chemistry firstly we should have good knowledge of mole concepts because it is root of Physical chemistry and we all knew that without root nothing could.
Here are some useful Topics of Physical chemistry which I describe in another sections:
1.The Mole Concept
2.Stoichiometry
3.Gas Analysis
4.Atomic Weight
5.Molecular Weight
6.Chemical Equivalenece
7.Volumetric Calculations
8.Electrolysis
9.Estimation of Elements in Organic Compounds
10.Empirical, Molecular and Structural Rormulae
11.Atomic Structure and Radioactivity
12.Properties of Gases
13.Dilute Solution and Colligative Properties
14.Chemical Thermodynamics
15.Chemical Equilibrium
16.Ionic Equilibrium in Aqueous Solutions
17.CHemical Kinetics
18.Electromotive Force
19.Oxidation Number and Balancing of Redox Reaction
20. Solid and Liquid States
21.Solid and Liquid States
All above topics I described in stage by stage so read regularly and gain your knowledge.
GOOD LUCK