Lunes, Marso 26, 2012

The Six Chemical Reactions

chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity. 

All chemical reactions can be placed into one of the six categories. Here they are, in no particular order:

1) Combustion: A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:
C10H8 + 12 O2 ---> 10 CO2 + 4 H2O

2) Synthesis: A synthesis reaction is when two or more simple compounds combine to form a more complicated one. These reactions come in the general form of:
A + B ---> AB
One example of a synthesis reaction is the combination of iron and sulfur to form iron (II) sulfide:
8 Fe + S8 ---> 8 FeS

3) Decomposition: A decomposition reaction is the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:
AB ---> A + B
One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:
2 H2O ---> 2 H2 + O2

4) Single displacement: This is when one element trades places with another element in a compound. These reactions come in the general form of:
A + BC ---> AC + B
One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:
Mg + 2 H2O ---> Mg(OH)2 + H2

5) Double displacement: This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:
AB + CD ---> AD + CB
One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:
Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3

6) Acid-base: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:
HA + BOH ---> H2O + BA
One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:
HBr + NaOH ---> NaBr + H2O

Sabado, Pebrero 18, 2012


1.Begin by viewing the table. The rows are called periods and are listed in order of their atomic number from lowest to highest. The atomic number represents the number of protons found in the nucleus of their atoms. The columns are called groups. The groups are considered the most important means of identifying the metals. The groupings are called alkali metals, alkali earth metals, halogens, noble gases, transition metals, rare earth metals, other metals and other non-earth metals. The groups indicate similar chemical properties and the same type of electron configurations in their valence shell.
The electrons in the outer shell are called valence electrons, which determine how reactive a metal is to other metals. The Roman numerals above each group of elements specify the usual number of valence electrons. The "a" and "b" included next to the Roman numerals determine where the electrons reside. Representative elements are "a" and their electrons reside in the "s" and "p" sub-levels. The non-representative elements are "b" and their electrons reside in the "d" and "f" sub-levels.

Look at the table and find iron, or Fe. Fe stands for the Latin word ferrum. Fe has a series of numbers around it. To locate iron find it in group 8 VIIIb. Above the abbreviation of Fe is its atomic number, which is 26. Usually below the Fe is the atomic weight, which is 55.847. Some periodic tables vary to some degree in the information and configuration but the atomic number and atomic weight will be present.

 Notice a separate group of metals at the bottom. This group is called the rare earth metals. Most of the rare earth metals are man made. There are 30 of these metals, and they reside in group 3 in rows 6 and 7. These metals comprise two series of metals called lanthanide and actinide.