Chemistry is that branch of science under which the properties, composition, structure and changes in substances are studied.The word chemistry is derived from the ancient name of the country of Egypt, Chemia. The word alchemy means black colour. Due to the black color of the soil of Egypt, its ancient name was alchemy. In ancient times the art of Egypt was at its peak.
The word chemistry is probably the "art of theEgyptians".(Egyptian Art). There is no doubt that in ancient times chemistry emerged as an art, but nowRasa is not an art but a science.Chemistry is an experimental science that deals with the study of substances. In view of the extraordinary development of chemistry, it has been divided into several sub-branches.
The following are the main branches of chemistry:
1. Inorganic chemistry: Under this, all the elements and their compoundsare studied (except organic compounds).
2. Organic chemistry: Study of compounds of carbon under thisis done.
3. Physical chemistry: Under this, the laws and principles of chemical reactions are studied.
4. Analytical chemistry: Under this, the methods of identifying substances and determining their quantity are studied.
5. Industrial chemistry: Under this, the rules, reactions, methods, etc. related to the manufacture of substances in large quantities are studied.
6. Bio-chemistry: Under this, chemical reactions occurring in living beings and substances obtained from animals and plants are studied.
7. Agricultural chemistry: Under this, chemicals related to agriculturestudy is done.
Classification of substance
Heterogeneous substances: The substances which contain two or more parts of different types are called heterogeneous substances. For example, a mixture of water and oil or a mixture of water and ice are heterogeneous substances. Similarly, milk, blood, smoke, clouds, gunpowder, soil etc. are heterogeneous substances.
Homogeneous substances: The substances in which every part is of the same type are called homogeneous substances.All metals like iron, mercury, copper etc., oxygen, nitrogen, hydrogen, ammonia etc. all gases and mixtures of gases, solutions of substances and all pure substances are homogeneous substances.
Homogeneous substances are of two types
1. Solution:
A homogeneous mixture of two or more pure substances is called a solution. A solution does not have a definite composition.
2. Pure substances:
Homogeneous substances whose composition is fixed and constant are called pure substances. All elements and compounds are pure substances.
Elements:
Pure substances made up of atoms of the same type (same atomic number) are called elements. For example, H, N, O, S, Na, Cu, Hg etc. are elements. So far 114 elements have been discovered. Out of which 24 elements are man-made elements by artificial methods.
Compounds:
A pure substance formed by a chemical combination of atoms of different types (different atomic numbers) in a definite proportion is called a compound. A compound can be decomposed into two or more different types of atoms (elements). For example, HO, NH3, CO2, NaCl, CH etc. are compounds.
Physical Changes
Changes in which no new substance is formed are called physical changes. In physical change, the chemical composition and molecular structure of the substance do not change. Following are the characteristics of physical change:
(1) In physical changes, new substances are not formed (basic characteristic).
(2) The characteristic properties of the original substance do not change in physical changes, that is, the chemical nature of the substance does not change (basic properties).
(3) Physical changes are usually temporary. The process lasts only as long as the cause of the process lasts. When the cause of the process is removed, the process reverses (secondary symptom).
Changes in the physical state, condition, shape, size, volume etc. of substances are physical changes. Processes like melting, evaporation, condensation, freezing etc. of substances and processes like distillation, sublimation etc. are physical changes.
Chemical Changes
Changes in which new substances are formed are called chemical changes. In a chemical change, the chemical composition of the original substance and its molecular structure or only the molecular structure changes. The following are the characteristics of a chemical change:
(1) The properties of matter change in chemical changes, that is, the chemical nature of matter changes (basic character).
(2) In a chemical change, new substances are formed, whose properties are different from those of the original substance.(basic symptom).
(3) Chemical changes are usually permanent. Procedure on removal of reason for changeDoes not reverse (secondary symptom).
(4) Energy changes in chemical changes are more than in physical changes. In these changes, heat, light, etc., are often released or absorbed (secondary symptoms).
Burning of substances, rusting, fermentation, combination reactions, decomposition reactions, allotropic changes, isomeric changes and all other chemical reactions are chemical changes.
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