Absolute Temperature is temperature measured on the absolute scale of temperature (i.e. the thermodynamic scale of temperature), and may be reported by adding 273 to the Centigrade temperature.
The Absolute Zero of Temperature is the lowest temperature on the thermodynamic scale of temperature and is -273 degC.
Absorption is the process whereby a gas is taken up and dispersed in the bulk of a solid or a liquid, or where a liquid is taken up and dispersed in the body of a solid.
Absorption Spectra result from the interaction of electromagnetic radiation with matter, where the energies that are removed from the continuous spectrum of light by the absorption medium show up as black lines or bands. The absorption spectrum of a substance is obtained by passing a beam of light through the substance in a spectrometer and examining the light that emerges. When a substance is capable of emitting a spectrum, the lines of the emission spectrum are in exactly the same positions as the lines and bands in the absorption spectrum.
The Natural Abundance of an Isotopes is the ratio of the number of atoms of a particular isotope of an element to the total number of atoms of all the isotopes present. It is often expressed as a percentage.
The Abundance of Substances is the ratio of the total mass of a specified element in the earth's crust to the total mass of the earth's crust. It is often expressed as a percentage.
Acid-Base Indicators are used when an acid is titrated against a base in Volumetric Analysis, to give a visual indication of the end-point of the titration. An acid-base indicator usually changes colour over a range of about 2 pH units.
Each indicators change colours at a different and unique pH.
An Acid-Base Titration is the analytical technique in Volumetric Analysis , where an acid of known concentration is used to neutralise a known volume of a base, and the observed volume of the acid required is used to determine the unknown concentration of the base.
An acid-base indicator is used to determine the end-point of the titration.
These are Organic compounds containing the group ---CO.X , where X is a halogen . Acyl chlorides, have the general formula R.CO.Cl. In systemically naming acyl halides the names end with the suffix -oyl, e.g. ethanoyl chloride CH3COCl.
Reactions of Acyl Chlorides
Acyl chlorides react readily with alcohols,
RCOCl + R'OH ===> RCOOR' + HCl
water, phenols and amines they are used in acylaction reaction.
Preparation of Acyl Halides
The --OH group in Carboxlyic acid is replaced by a halogen using a halogenating agent such as PCl5.
Those oxides which form acidic solutions on reaction with water are called acidic oxides, (or sometimes acid anhydrides).
The acidic oxides are the oxides of the non-metal elements.
The acid anhydrides are called by their systematic names (e.g. sulphur dioxide, nitrogen pentoxide, etc.).
Most acidic oxides are soluble in water and react with it giving acids in solution.
For example, sulphur trioxide reacts with water to produce sulphuric acid.
SO3 + H2O ==> H2SO4
All acidic oxides react with alkalis to give salt and water only. For example, sulphur trioxide reacts with sodium hydroxide in aqueous solution to produce sodium sulphate and water.
SO3 + 2 NaOH ==> Na2SO4 + H20
Similarly, nitric oxide reacts with sodium hydroxide in aqueous solution to produce a mixture of sodium nitrate, sodium nitrite and Water.
2 NO2 + 2 NaOH ==> NaNO2 + NaNO3 + H2OAcidic oxides also include the giant molecular lattices (e.g. silicon dioxide).
Acid Rain results from the burning of fossil fuels containing sulphur, when sulphur dioxide is produced during the combustion process.
Although the nitrogen in the air is normally uncreative, nitrogen oxides are also produced during the high temperature combustion process.
Sulphur dioxide and nitrogen oxides, NOx, are toxic acidic gases which readily react with the water in the atmosphere to form a mixture of sulphuric acid, nitric acid and nitrous acid. The dilute solutions of these acids which result give rain water a far greater acidity than normal (i.e. a lower pH) and this is known as acid rain.
When the oxides of non-metals reacted with water they formed acids. For example, when sulphur dioxide is dissolved in water, an acidic solution of Sulphurous Acid results.
SO2 + H2O ==> H2SO3.
Similarly, the oxides of metals react with water to form bases. For example, when sodium oxide reacts with water, sodium hydroxide (i.e. caustic soda) is formed.
Na2O + H2O ==> 2 NaOH
The Actinides all have two outer s-electrons (i.e. having a7s(2) electronic configuration). The Lanthanoids and Actinides make up the f-block.
The activation energy of a chemical reaction is the minimum energy required to initiate the chemical reaction (i.e. cause the chemical reaction to take place). It is the energy required to overcome the energy barrier, so that the reaction can proceed.
During the course of a chemical reaction, energy must be supplied to stretch and break the bonds in the reactant molecules, and the energy required for this process is termed the activation energy. New bonds are then reformed during the course of a chemical reaction, to make the products of the reaction.
This reaction involves the introduction of an acyl group (RCO--) into a compound.
Method
An Alkyl halide is reacted with an alcohol or a carboxylic acid anhydride e.g.
RCOCl + R'OH ===> RCOOR' + HCl
The introduction of an acetyl group (CH3CO--) is Acetylation, a process used for protecting --OH groups in Organic synthesis.
For example, bromine adds across the double bond of ethene (i.e. Ethylene) in an addition reaction to form dibromoethane.
CH2=CH2 + Br ==> H2BrCH2Br Ethene Bromine Dibromoethane
Adsorption is the surface phenomenon involving the attachment of a gas or liquid to the surface of a solid. This surface property of solids is exploited in Chromatography for the separation of mixtures.
Air pollution is the degradation of the quality of the atmosphere by chemical and particulate contamination. Acid Rain is a manifestation of the deterioration of the quality of the atmosphere as a result of the combustion of fossil fuels. See also Atmospheric Pollution
Alchemy was the so-called black art of renaissance Europe which sought ways of converting everyday substances into gold.
Alcohols are the homologous series of organic compounds of general formula, ROH, where R is any alkyl group or substituted alkyl group. An alcohol may be a primary alcohol, secondary alcohol, or tertiary alcohol, depending on whether the carbon atom attached to the hydroxyl group, -OH, is combined with an alkyl group attached to one, two or three carbon atoms, respectively.
Alicyclic compounds are ring compounds containing single and/or multiple carbon to carbon bonds. Alicyclic compounds do not contain the conjugated double bonds which are characteristic of aromatic compounds.
An aliphatic compound is an organic compound which consists of carbon and hydrogen in a structure which consists of
The alkenes, (i.e. the olefins), are the second homologous series of hydrocarbons, where there is at least one double-bond between the carbon atoms in the molecules.
The alkenes are said to be unsaturated because of the existence of a multiple bond in the molecule. The general structure of the alkene series of hydrocarbons is CnH2n. The first member of the ethene series is ethene, (previously called ethylene). In the case of higher members of the alkene series, the double bond may be between the terminal carbon atoms of the chain, or may be between internal carbon atoms in the chain.
Ethene C2H4 CH2=CH2 Propene C3H6 CH3CH=CH2 Butene C4H8 CH3CH2CH=CH2 Pentene C5H10 CH3CH2CH2CH=CH2 Heptene C6H12 CH3CH2CH2CH2CH=CH2 Hexene C7H14 CH3CH2CH2 CH2CH22CH=CH2 Octene C8H16 CH3CH2CH2CH2CH2CH2CH=CH2 Nonene C9H18 CH3CH2CH2CH2CH2CH2CH2CH=CH2 Decene C10H2O CH3CH2CH2CH2CH2CH2CH2CH2CH=CH2Ethene, propene and butene are planar compounds. The first bond on the unsaturated carbon atoms are sp2 hybrids, and these bonds are arranged as far apart in space as possible (i.e. at 120 degree in the same plane). These are s bonds (sigma bonds) and are formed by the end-on overlap of sp2 hydride orbitals of the carbon atoms. The second bond that makes up the double bond of the unsaturated carbon atoms in alkenes is a p-bond (pi-bond), formed by the side-on overlap of the p-orbitals of the carbon atoms. p-bond (pi-bonds) are much more reactive than the s bonds (sigma bonds).
An alkyl group or an alkyl radical, is structurally similar to an alkane group, where a hydrogen atom is missing. Alkyl radicals are named by replacing the ending "-ane" from the name of the alkane, with the "-yl" suffix.
An acidic oxide and a basic oxide react directly with each other to form salts.
For example, sulphur trioxide reacts with sodium oxide to form sodium sulphate.
SO3 + Na2O ==> Na2SO4