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The complex series of reactions by which nitrogen is slowly but continually recycled in the atmosphere, lithosphere and hydrosphere.

 

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Hydrogen

Discovered : by Henry Cavendish in 1766.
Isolated in London, UK.
Origin : The name is derived from the Greek ‘hydro genes’, meaning water forming.
Description :A colourless, odourless gas that burns and can form an explosive mixture with air. It is currently manufactured from methane gas, but is also produced by the electrolysis of water and aqueous salts. The gas is used to make such key materials as ammonia, cyclohexane and methanol, which are intermediates in the production of fertilisers, plastics and pharmaceuticals. Some see hydrogen gas as the clean fuel of the future - generated from water and returning to water when it is oxidised. Hydrogen-powered fuel cells are increasingly being seen as pollution-free sources of energy.

Valence Bond Theory

Assumes that covalent bonds are formed when atomic orbitals on different atoms overlap and the electrons are shared.

Periodic Table

An arrangement of elements in order of increasing atomic numbers that also emphasizes periodicity.

Isomorphous

Refers to crystals having the same atomic arrangement.

Line Spectrum

An atomic emission or absorption spectrum.

Natural Radioactivity

Spontaneous decomposition of an atom.

Secondary Standard

A solution that has been titrated against a primary standard. A standard solution is a secondary standard.

 

What are Compound Microscopes?

Most of the microscopes used today are compound. A compound microscope features two or more lenses. A hollow cylinder called the tube connects the two lenses.

The top lens, the one people look through, is called the eyepiece. The bottom lens is known as the objective lens. Below the two lenses is the stage, with the illuminator below that.

Denatured

A commercial term used to describe ethanol that has been rendered unfit for human consumption because of the addition of harmful ingredients to make it sales tax-expempt.

 

Hess' Law of Heat Summation

The enthalpy change for a reaction is the same whether it occurs in one step or a series of steps.