Chemistry is the study of chemicals, elements, processes occurring around us in day to day lives and everything which involves basic non-reversible change. Taking some general examples like: burning of paper, setting of curd, process of photosynthesis. Such processes are termed as “Chemical Process” or chemical changes.
As mentioned earlier chemistry deals with the study of chemical and non-reversible changes, to find out the mechanism behind such processes and understand the reasons and facts of the process chemistry, was introduced. Each mechanism has a certain output or in chemical terms if say a specific “product” which has its own characteristic properties. These properties can further be classified as “physical properties” and “chemical properties”. A small change in general mechanism of the process may result a major change in the product as well as its properties. For example: Setting up of curd is an action of bacteria known as “lacto bacilli”, but before mixing it with milk, the milk has to be heated (not boiled) up to the temperature of 65-70 ̊C so that a thick creamy curd is obtained. Hence to understand the interesting facts behind a process chemistry is studied.
A Chemical Reaction is a symbolic representation of a chemical process using the defined symbols for various elements involved in the process. The reaction shows us mechanism which a chemical process is undergoing. For Example: Water is formed when 2 units (molecules) of Hydrogen (H) combine with one mole of oxygen(O). this process can be represented as: 2H2 + O2 -> 2H2O. such description is called as a chemical reaction equation; and the process defined is called as chemical reaction. The LHS of the equation is known as “reactant side” and the RHS is known as the “product side”
Chemistry being a vast and expanded field required further classification which could help studying the subject in a better and easy manner. The “classification of chemistry” is as follows:
GENERAL TERMS INVOLVED:
Concepts of Chemistry: To start the study of chemistry first we need to understand some of its tools which make it easier to understand the subject and t correlate the facts to be learnt ahead.
AVOGADRO NUMBER: NA = 6.022×10^23. It is a constant value which is equal to the number of particles present in a Carbon-12 isotope.
How it can be used:
To calculate the number of atoms, ions, molecules and other particles, present in given number of moles.
Solution: first we will calculate the number of moles of water using the formula
N = g/M where N→number of moles g→given mass of the compound M→molar mass of the compound According to question: N = 62/18 = 3.44 Hence number of moles = 3.44 To calculate the number of particles we use the formula Number of particles = N×NA = 3.44×6.022×10^23 = 20.71×10^23 Hence the number of molecules in 62gram water are 20.71×10^23.
Concept of molar mass, atomic mass and atomic mass unit:
Generally, masses are measured for objects which are bulky and have a rigid structure. but what about masses of atoms and other particles! As mass has an SI unit as Kg(kilo-gram), similarly mass of an atom is expressed in terms of atomic mass unit (amu). Atomic mass Unit is defined as the atomic mass or molecular weight of an atom equal to one-twelfth the mass of a carbon-12 atom.
Since concept of amu became bit complicated it was suggested that simpler units would be used and then molar or atomic mass was defined. molar mass or the atomic mass for an entity is defined as the mass of the number of protons and neutrons present in an atom. Mass of neutron: 1.674929 x 10-27 kg
Mass of proton: 1.672623 x 10-27 kg
Hence atomic mass of an atom could be calculated easily now.
|1 atomic mass unit||1.660540 x 10-27||1.000|
|Neutron||1.674929 x 10-27||1.008664|
|Proton||1.672623 x 10-27||1.007276|
|Electron||9.109390 x 10-31||0.00054858|
ATOM: an atom is defined as the basic unit of a substance which can no further be broken. its constituents are neutrons, electrons, and protons.
Locations of these particles:
Neutrons and protons are located at the center of the atom and hence the mass of atom is contained at the nucleus
While electrons are held at the outer shells (energy levels) where they keep on revolving around the nucleus.
Number of protons is equal to the number of neutrons. Electrical neutrality is maintained in the atom due to the equal number of protons and electrons present in it. Neutrality is disturbed when either a positive or a negative charge is introduced to a neutral atom.
Being the smallest unit, atoms do play key role in formation of new compounds either by sharing their electrons or by placing an extra electron or by removal of an electron. Yet its size is small but it has a huge significance in the chemical studies.
Concentration terms and their significance:
While studying chemistry it becomes very important to determine the amount of substance or compound which we are dealing with. So, to understand that, concepts of molar concentration were introduced. Concentration of a compound in a mixture is defined as the amount of substance present in each solution at NTP. Now to measure the concentration new terms were introduced such as:
(a) Molarity: Molarity is defined as the number of moles of solute per liter of solution.
M = number of moles of solute(mol)/Volume of Solution in Liters(L)
Hence SI unit for molarity is mol/L
(b) Molality: Molality is defined as number of moles of solute per Kg of solvent.
m = number of moles of solute(mol)/Mass of solvent in kilogram(kg)
Hence SI unit for normality is mol/Kg
(c) Normality: Normality is defined as the gram equivalent weight of solute per liter of solution.
N = gram equivalence of solute/Volume of solution in liter (L)
Hence SI unit of normality is equivalentweight/L, hence is represented as (N)
(d) Mole Fraction: Mole Fraction is defined as the ratio of the number of moles of reactant A to the total number of moles.
Suppose a reaction happens like: A+B→C where number of moles of A = NA And number of moles of B = NB
Then mole fraction of A w.r.t B is χAB = NA/NA+ NB
Note that mole fraction of B w.r.t A would be χBA= NB/NA+ NB
*Or NA+ NB=1
Concepts discussed above included picturizing chemistry in our day to day lives, classification of chemistry, ease of studying chemistry using various tools like stoichiometry and mole concepts, concept of concentration term and their significance along with their application would definitely help the reader in building up interest in chemistry and seeking for the reasons behind various processes happening around us all the time.
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