In this article, we shall study the meaning of chemistry and its different branches.

What is Chemistry?

Science word is derived from the Latin word ‘Scientia’ which means ‘to know’. Science has many disciplines, Chemistry is one of them. It is the study of materials that make up the universe and changes which these materials undergo.

It is defined as the study of the composition, structure, and properties of matter and the reactions by which one form of matter may be converted into another form.

Chemistry is a central science. It can be explained as follows. Study of chemistry is being done from the ancient time all over the world. It is ancient science but its major development has taken in the modern era. Chemistry provides the support structure to all other sciences like physics, biology, geology, environmental science and engineering.

The significance of the Study of Chemistry:

Food: 

Artificial sweetener, flavouring agent, food preservatives are chemical compounds and are man-made.

Green revolution in India has taken place due to the use of mechanized agriculture with the use of chemical fertilizers, insecticides, pesticides etc.

Sodium benzoate, sodium meta bisulphate, and salicylic acid are food preservatives.

Clothing: 

We get cotton, wool, jute, silk as natural fibres (fibres) for making clothes. But synthetically prepared fibres like nylon, rayon, dacron are superior to the natural fibres.

Shelter:

For shelter steel, aluminium, copper, plastic is required. They are extracted or produced by chemical processes.

Medicines:

Antibiotics, synthetic drugs, antiseptics, anaesthetics, antipyretics, analgesics, vitamins and hormones are used in the improvement of human life.

Some important drugs areTaxol (a Life-saving drug for cancer ), Cisplatin (Cancer therapy), Azidothymidine (AIDS treatment), Prophylactics (Disease preventing), L-Dopa (Parkinson’s disease), Human insulin (Diabetes treatment), Tamiflu (Swine flue).

Agriculture:

Chemical fertilizers like urea, calcium nitrate, ammonium sulphate etc. and insecticides like D.D.T.  (dichloro diphenyl trichloroethane),  gammexane, methoxychlor etc. are used for the improvement of agricultural yield.

Transportation and Electrical Energy:

Fuels like petrol, diesel, C.N.G. etc. are good fuels which are used in automobiles. This energy can be used to generate electrical energy. In the field of electrochemistry Daniel cell, a Lead storage cell, dry cells, fuel cells are used to produce electricity.

Energy resources:

Petroleum, wood, coal, charcoal, nuclear fuel are chemical substances which are used to satisfy our energy requirements.

Health:

Carbohydrates, proteins, fats, vitamins and minerals are the chemical substances which are required for the maintenance of our body functions and health.

Industry and Everyday Life:

kerosene, gasoline, petrol, diesel, compressed natural gas (C.N.G.), liquefied petroleum gas (L.P.G.), Paraffin (Wax), Vaseline, Boot Polish, Fibres like wool, silk, cotton, jute, Synthetic fibres like nylon, terylene, polyester, Solvents like water, chloroform, alcohol, benzene, acetone, carbon tetra chloride , substances like poly vinyl chloride (PVC), polyethylene, bakelite, rubber, Paints, varnishes, dyes, indigo, azodyes, printing inks, detergents, soaps, perfumes, insecticides, fertilizers are chemical  compounds.

All engineering materials like iron, steel, stainless steel, aluminium, zinc, tin, copper, galvanized steel, alloys like brass, amalgams, precious metals like silver, gold, platinum are extracted, purified, synthesized, analyzed using processes based on chemical technology.

Education:

There are para chemical branches like Biochemistry, Biotechnology, Pharmacy, Herbal Science, Toxicology, Archaeology and Environmental Science.

Branches of Chemistry:

Different branches of chemistry are

Physical Chemistry:

The branch of chemistry that deals with the structure of matter, the energy change and theories, laws, principles that explain the transformation of matter from one form to another.

Inorganic Chemistry:

This is the branch of chemistry that deals with the chemistry of elements other than carbon and their compounds.

Organic Chemistry:

This is the branch of chemistry that deals with the chemistry of carbon and its compounds.

Analytical Chemistry:

This is the branch of chemistry that deals with the separation, identification and quantitative determination of compositions of different substances.

Industrial Chemistry:

This branch deals with the chemistry involved in industrial processes

Nuclear Chemistry:

This branch deals with the study of nuclear reactions as nuclear fission, nuclear fusion and transmutations.

Biochemistry:

This is the chemistry of the substances consisting of living organisms.

In the next article, we shall discuss the chemical classification of substances viz: Pure substances, mixtures, elements, compounds, and their characteristics.

Next Topic: Chemical Classification of Substances

Science > Chemistry > Introduction to Chemistry > Significance of the Study of Chemistry

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In this article, we shall study the concept of energy, types of mechanical energies, and the law of conservation of energy

Energy:

Different types of energy are mechanical energy, sound energy, heat energy, light energy, chemical energy, electrical energy, atomic energy, nuclear energy. Mechanical energy is further classified into kinetic energy and potential energy.

Kinetic Energy:

The energy possessed by the body on account of its motion is called kinetic energy. e.g Energy possessed by flowing water and wind, moving bicycle

Consider a body of mass ‘m’ lying on the smooth horizontal surface, is acted upon by a constant force of magnitude ‘F’ which displaces it through a distance ‘s’ in its own direction. Then the work done by the force is given by

W  =  F .  s     ……….. (1)

By Newton’s second law of motion

F  =  m . a     ……….. (2)

Where ‘a’ is the magnitude of the acceleration in the body.

From equations  (1) and (2)

∴  W  =  m a s  …………… (3)

By equation of motion we have

v² = u²   +  2as

Where u  = magnitude of the initial velocity. In this case u = 0

v =  magnitude of final velocity after covering the distance ‘s’

∴  v² =  2 a s

∴ as =  v²/2

Substituting in equation (3) we get

∴  W  =  mv²/2

∴  W  =  ½mv²

This work is stored as kinetic energy in the body. Thus the kinetic energy of the body is given by

K.E. = ½mv²

This is an expression of the kinetic energy of a body.

Potential Energy:

The energy possessed by a body or a system on account of its position and configuration is called potential energy. e.g. energy possessed by water stored in a dam, in wound spring of a watch

Suppose that body of mass ‘m’ be raised to some height say ‘h’ against the gravitational force which is equal to the weight of the body ‘mg’. Where ‘g’ is an acceleration due to gravity.

As the applied force and the displacement of the body are in the same direction.

Work = Force × Displacement

W = mg × h

∴  W = mgh

This work is stored as the potential energy in the body.

∴  P.E. = mgh

This is an expression for the gravitational potential energy of a body, raised to some height above the earth’s surface.

Units and Dimensions of Energy and that of Work are the Same:

The capacity of a body to do work is called energy. Hence energy is measured in terms of work. Therefore, the units and dimensions of energy and that of work are the same.

kilowatt-hour:

a kilowatt-hour is a unit of measuring energy. This unit is a general unit of energy consumption bills (Electricity bills)

Now Work = Power x time

Hence, 1 kilowatt hour= 1 kilowatt × 1 hour

If the power of 1 kilowatt is used for 1 hour, the work done or energy consumed is said to be 1 kilowatt hour.

1 kWh   = 1kW x 1 hour

= 1000 W x 60 x 60 sec

= 1000 J/s x 3600 s

= 3600000 J

= 3.6 x 10⁶ J

Kinetic Energy is Always Positive:

The kinetic energy of a body is given by the expression. K.E. = ½mv²

The right-hand side contains the term mass ‘m’ which is always positive and a term square of velocity which is also positive. Thus the right-hand side of the expression is always positive. Thus kinetic energy is always positive.

Principle of Conservation of Energy:

The energy cannot be created nor it can be destroyed but can be converted from one form to another. Thus the total energy of the isolated system remains the same.

Energy can be converted from one form to another Examples

• In an electrical bulb, electrical energy is converted into light energy and heat energy.
• When the hammer strikes the nail mechanical energy gets converted into sound energy and heat energy.

Working of Hydroelectric Power Station :

The principle of conservation of energy can be explained by the example of a hydroelectric power station.

Water is stored in the artificial reservoirs created in the mountains by constructing a dam across the river. Thus the kinetic energy of flowing water is converted into potential energy of stored water. This stored water is brought downhill i.e. at the foot of the mountain through pipes. This water is then directed on blades of the wheel of the turbine. Thus the kinetic energy of water is used to rotate the coil in the turbine. Due to rotation of the coil in the magnetic field the kinetic energy gets converted into electrical energy. This energy can further be converted into different forms of energy like sound, heat, light, magnetism, etc.

Principle of Conservation of Mass:

The mass cannot be created nor it can be destroyed but can be converted from one form to another. Thus the total mass of isolated system remains the same.

Einstein’s Mass-Energy Relation:

According to Albert Einstein, the mass and energy are interconvertible and the equivalence between them is given by the relation

E  =  m c²

Where   E = amount of energy

M = Mass

c = speed of light in vacuum

This relation is known as Einstein’s mass-energy relation.

Thus mass and energy are not two different physical quantity or the mass is a form energy.

Examples of Mass-Energy Interconversion:

Phenomenon of pair production :

In the phenomenon of pair production, the energy of gamma rays photons is converted under proper conditions, into a positron-electron pair. Thus here energy gets converted into mass.

Phenomenon of pair annihilation:

In the phenomenon of pair annihilation, a positron and electron under proper conditions combine to form the gamma-ray photon. Thus the particles (mass) are converted into energy.

Note:

Positrons and electrons both are similar particles having the same mass only difference is their charges. Positrons are positively charged while electrons are negatively charged.

Modified Law of Conservation of Mass and Energy:

The total amount of mass and energy in the universe is always constant.

Einstein’s Formula for the Variation of Mass with Velocity:

When the velocity of light is comparable with that of light, then, the mass of the particle in motion is given by

Where m_o = mass of a body at rest.

m = mass of a body when moving with a velocity ‘ v ’

c = velocity of light in vacuum.

This relation is known as Einstein’s formula for the variation of mass with velocity. This relation shows that the mass of a body increases with the increase in its velocity.

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The internal energy can be defined as the sum of all possible kinds of energies that a system possesses. Every chemical reaction is associated with heat change. Heat is either evolved or absorbed.  This is possible only when every substance involved in chemical reaction possess certain fixed amount of energy which is called internal energy. Every substance is composed of molecules, atoms and subatomic particles.  The position and motions of the molecules, atoms and subatomic particles is the origin of internal energy.

Constituents of Internal Energy:

Kinetic or Thermal Energy:

The energy that a body possesses due to its movements is called as kinetic energy. Since kinetic energy depends upon the temperature it is called thermal energy.  Thermal energy is directly proportional to the temperature. K.E. is of three types

Translational Energy (E_trans):

The energy associated with the molecules due to the continuous, rapid, random movements along straight line path is called translational energy. Molecules of gases or liquids are in a state of constant random movement. Hence the molecules of gases and liquids have translational energy.

Vibrational Energy (E_vibr):

The energy associated with the molecules due to atomic vibrations is called vibrational energy.

There is a repulsive force between nuclei of two atoms, and electrons of two atoms.  There is an attractive force between the nucleus of one atom and electrons of other atoms and vice versa. As a result of these attractions and repulsions, atoms are in a state of to and fro movement.  Vibrations are of two types viz. stretching and bending vibration.

Rotational Energy  (E_rot):

The energy associated with the molecules by virtue of their rotations about their axes is called as rotational energy. All diatomic and polyatomic molecules rotate about an axis perpendicular to the axis of molecule.

Thus   the total kinetic energy of the system is given by

K.E.  = E_trans + E_vibr +  E_rot

Potential or Bonding Energy:

The energy associated with the body by virtue of its position is called is potential energy. Potential energy is independent of temperature.  It arises due to the bonding between atoms in a molecule. It is classified into two types.

Intermolecular Energy (E_intermole):

The amount of energy required to separate molecules from each other is called as intermolecular energy. In solids and liquids, molecules are held together by means of weak physical forces of attraction called Vander Waals forces. These forces are strong in solids hence intermolecular energy is more in solids than in liquids.

Intramolecular Energy (E_intramole):

The energy required to break the molecule into its constituent atoms is called as intramolecular energy. Atoms are held together in the molecule by certain electrostatics force of attraction called the chemical bond.  So intramolecular energy is nothing but the energy required to break chemical bonds so as to isolate constituent atoms from each other.

Thus the total potential energy of the system is given by

P.E. =   E_intermole + E_intramole.

Total Internal Energy of a System:

Internal energy is the sum of K.E. and P.E. The absolute value of it cannot be determined but the change in it can be determined.

Significance of Internal energy:

• It depends on the quantity of a substance, hence it is extensive property.
• Change in it represents the heat evolved or absorbed in a reaction at constant temperature and constant volume.
• For isothermal process change in it is zero.
• For the process involving the evolution of energy change in it is negative and for the process involving absorption of energy change in it is positive.

Characteristics of Internal energy:

• The internal energy of a system is extensive property.
• It is a state property. The change in internal energy is independent of the path followed.
• Change in it of a cyclic process is zero.

Notes:

• In practice, the absolute value of internal energy (U) is not known and cannot be measured because it is very difficult to determine accurately the most of the quantities that contribute to the internal energy of a system. But in thermodynamics, the quantity internal energy (U) is not important while the change in it (ΔU) is important.
• The quantity change in internal energy (ΔU) is associated with many other thermodynamic quantities by simple mathematical relations. Using those relations the change in internal energy (ΔU) can be determined. Such relations are ΔH = ΔU   +  PΔV  and ΔH = ΔU   + ΔnRT Hence  the change in internal energy (ΔU) can be determined.

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