Endothermic & Exothermic Reaction, Star & Planet, Nuclear Fission & Fusion

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Endothermic & Exothermic Reaction

Exothermic Reaction

  • Energy is drawn in from the external environment, causing its surroundings to lose heat, or “cool down.”
  • The endothermic chemical reaction creates a product that has a higher energy level than the original materials, causing the reactant՚s stored energy to decrease. (In scientific terms, the reactants have “less total enthalpy” than the product.)
  • The resulting product of the reaction is less stable because, the higher the energy bond, the less strength its molecules possess.
  • Most endothermic reactions are not spontaneous.
  • Example: Melting ice. In order for ice to melt, it needs to draw in the heat (energy) from its surroundings. The ice becomes less stable as it responds to the increased heat. The ice stored energy decreases. The end product is water, which has a higher energy level than the ice.

Exothermic Reactions

  • Exothermic chemical reactions cause their surroundings to warm up by giving off heat.
  • The reactants contain more stored energy than the product because energy from external sources is not required, but given off. This gives the product more stability due to the lower amount of energy needed. (In this case, the reactants have a “greater total enthalpy” than the product.)
  • Exothermic reactions are usually spontaneous.
  • Example lighting a match. When the head of the match is struck, it results in the spontaneous release of stored energy (heat) from the reactants into the surroundings. The flame that is produced has a lower level of energy than the match and the striking surface because the reaction is giving off stored energy and not required to draw energy in from its surroundings

Star & Planet


  • Stars are self-luminous heavenly bodies.
  • They do not revolve around the sun.
  • They are usually stationary.
  • Examples: fixed stars, binary stars.


  • Planets are rocky non-luminous bodies.
  • They revolve round the sun.
  • They usually move.
  • Examples: Mercury, Venus, Jupiter etc.

Nuclear Fission & Fusion


  • Lighter atoms are fused together at a very high temperature to form heavier elements.
  • It is difficult to carry out on the earth.
  • It has no nuclear waste problem.
  • It requires cheaper and abundant elements.
  • Not possible at concerning scale as high temperature is needed to start it.


  • Heavier unstable atoms are broken down to produce energy.
  • It is easy to carry out on the earth.
  • It has nuclear waste radioactivity disposal problem.
  • It requires expensive and rare elements.
  • Possible to commercialize under controlled measure.


  • It stands for random access memory.
  • It is an optical disc, where data and information is stored permanently.
  • RAM is the primary storage media.
  • RAM is the primary storage device from which the system boots. (v) RAM is stored on RAM chip.
  • The data or information stored on it can be written on or it can be erased.


  • It stands for read only memory.
  • It is that part of CPU, where temporary information is stored.
  • RIOM is the secondary storage media.
  • System does not boot from ROM.
  • ROM is stored on a compact disc.
  • The data or information stored on it neither be written on, nor it can be erased.


  • A bit is defined as: a single basic unit of information, used in connection with computers and electronic communication. All modern computers store and use data in digital form. The smallest unit of storage and measurement is one binary digit, therefore its name.
  • A byte, pronounced bite, is the next size up basic unit of measurement for information storage, usually consisting of eight bits. These 8 bits are grouped together to form a byte that is, a total or 8 grouped bits representing one character of data. Therefore, so far we have two basic units of measuring digital information storage that have different capacities, they are:
    • 1 Bit
    • 8 Bits equal 1 Byte



It stands for Control Unit.

Control unit controls overall activates of computer.

CU does not perform the functions of calculations.


  • It stands for arithmetic logic unit.
  • It performs arithmetic and logical operations.
  • ALU performs functions of addition, subtraction, multiplication and division.

Hardware & Software


  • All the physical components of computer which can be touched, measured have weight and occupy space are collectively called computer hardware etc.
  • Examples of hardware are: keyboard, mouse, joy stick, scanner, printer, CPU etc.


  • Software can be defined as a set of instructions and codes written in a defined manner. In other words software are pre-written programs, which control the operation of computer.
  • Examples of software are; DOS, windows, UNIX, XENIX, Linus, JAVA, Oracle, Antivirus etc.

PC/Minicomputers & Mainframe Computers


  • It is a small computer based on microprocessor.
  • One user can use it at a time.
  • These are very low priced computers. An individual can afford it.
  • User friendly software are used to operate this computer.
  • Minicomputers were launched in 1959 by Digital Equipment Corporation (DEC) , (vi) Minicomputers are also made by Data General, Hewlett-Packard & IBM

Mainframe Computers

  • The largest computers called mainframe computers are the oldest category of computer system.
  • They are capable of great processing speed and data storage.
  • These are always kept in air-cooled rooms.
  • They are mainly used in banks, airlines and industrial companies.

Email & Snail Mail

Snail Mail

  • “Snail mail” is a term used to refer to mail that is sent in the traditional way — through the postal service — rather than by email, fax, or other electronic means of communication.
  • It is called “snail mail” because it can be very slow, as is a snail. Snail mail generally takes 2 or 3 days to go from origin to destination, if not many more,
  • Snail mail has gone out of fashion for simple letters, though it is still necessary for sending packages, or legal documents that require signatures.


  • Email is electronic mail which is very quick means of communication through computers and telephone line.
  • Email can be sent instantly.
  • With email, a message is sent directly from a user՚s mail program to another person՚s email address. Though many email messages simply contain words, they may also include photos or other digital files, such as songs, or links to websites.

Apes & Monkeys


  • Apes do not have tail.
  • Apes have rounded nasal openings.
  • Apes generally have bigger brains and larger bodies than monkeys.
  • Apes do not have web foot.
  • Apes are bigger in size.
  • Apes are: Humans, Chimps, Gorillas, Orangutans and Gibbons.


  • Monkeys have tails.
  • Monkeys have slanted nasal openings.
  • Monkeys have web foot.
  • Monkeys are smaller in terms of size
  • Monkeys are all primates′ non-apes and non-prosimians (lemurs)

Hydrostatics & Hydrodynamics


Hydrostatics is a branch of science which deals with physical behaviour of liquids at rest.

The consideration of liquids at rest, involves problems of buoyancy and flotation, pressure on dams and submerged devices, and hydraulic presses.


Hydrodynamics is the branch of science which deals with behaviour of liquids in motion.

The study of liquids in motion is concerned with such matters as friction and turbulence generated in pipes by flowing liquids, the flow of water over weirs and through nozzles, and the use of hydraulic pressure in machinery.

Comet & Meteor


Comet is a collection of gas, dust, and volatile ice that travel around the sun, generally in very eccentric orbit.


Meteor is a streak of light seen in the night sky signify the burning up in earth՚s atmosphere of inter-planetary material.

Barrage & Dam


  • Barrages are constructed not at a much height but at a low height.
  • Barrages are single purpose constructions i.e.. for irrigation.
  • Electricity cannot be produced in barrages.
  • It is constructed on plains.
  • Sukkur barrage is an example.


  • Dams are constructed at higher elevation or at a height.
  • Dam is multipurpose. It acts as reservoir, control flood, and for irrigation.
  • Dam is constructed to generate electricity.
  • It is impossible at ground level.
  • Tarbella dam is an example.


  • These are the elements having same atomic number but different mass number. They have the same atomic number because the number of protons inside their nuclei remains the same. The difference in their mass number is due to the difference in their number of neutrons.
  • Isobars Where Isotopes are chemically the same and physically different, the converse is true in Isobars. That is isobars are elements, which are chemically different but physically the same.
  • So, isobars are atoms of different elements having the same atomic mass but different atomic number. Since their number of electrons is different, their chemical properties are different.
  • The light nuclei have unstable isobars. Heavy nuclei have stable isobars and these occur in pairs. Suppose the number of protons of one isobar matches with that of another they are called as mirror-nuclides of each other.

Autopsy & Biopsy


  • An autopsy is the dissection and analysis of a dead subject.
  • Autopsies are limited to the deceased and there are two kinds of autopsy; External examination and internal examination.
  • Autopsy is performed for medico-legal purpose.


  • A biopsy is a medical test in which cells, tissue, or fluid is removed for examination.
  • Biopsy is not limited to only living people because they are routinely taken from organs that are going to be used for transplantation.
  • Autopsy is performed for diagnosis purpose.

Mitosis & Meiosis


  • Mitosis takes place within somatic cells (cells that make up the body) .
  • One single division of the mother cell results in two daughter cells.
  • A mitotic mother cell can either be haploid or diploid.
  • The number of chromosomes per nucleus remains the same after division.
  • It is preceded by a S-phase in which the amount of DNA is duplicated.
  • In mitosis, there is no pairing of homologous chromosomes.
  • There is no exchange of DNA (crossing-over) between chromosomes.
  • The centromeres split during anaphase.
  • The genotype of the daughter cells is identical to that of the mother cells.
  • After mitosis, each daughter cell has exactly same DNA strands.


  • Meiosis takes place within gamete cells (sex cells) .
  • Two divisions of the mother cell result in four meiotic products or haploid gametes.
  • A meiotic mother cell is always diploid.
  • The meiotic products contain a haploid (n) number of chromosomes in contrast to the () number of chromosomes in mother cell.
  • In meiosis, only meiosis I is preceded by a S-phase.
  • During prophase I, complete pairing of all homologous chromosomes takes place.
  • There is at least one crossing-over or DNA exchange per homologous pair of chromosomes.
  • The centromeres do separate during anaphase II, but not during anaphase I.
  • Meiotic products differ in their genotype from the mother cell.
  • After meiosis, each daughter cell has only half of the DNA strands.

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