Chemistry tutorials & FAQs!

Sodapop

CHF Hall of Fame
May 2009
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Montréal, QC
Introduction
Chemistry is the science branch that studies the structure, the composition and the properties of matter. It also studies the properties of the chemical reactions: the mixture of certain chemical substances and their results. Chemical reaction can be provoked by human, yes, but they can also happen naturally. Two types of reaction exists: the organic and the inorganic reactions. Organic reactions involve organic compounds such as methane.

Example of a well-known chemical reaction (water):
2H2 + O2 → 2H2O

Energy
is needed during any chemical reaction. It is needed to break the chemical bonds in the substances. When the new bonds are formed, the energy is released. By comparing the chemical energy of the original substances with the chemical energy of the final substances, you can decide if energy is released or absorbed in the overall reaction.

Two branches of chemical reaction exists: the endothermic reactions and the exothermic reactions (endo/exo means inside/outside, thermic means heat). If the reaction is exothermic, heat will be unleashed from the reaction, which will cause nearby heat around the chemical matter. If, on the other hand, it is endothermic, the matter itself will gain heat.

Example of a well-known exothermic reaction:
The reaction between gasoline and oxygen in a car's inner engine.

Important definitions:
Element
► Matter composed of atoms.
Atom
► The smallest particle of an element. It envelopes a positively charged nucleus that is surrounded by electrons.
Electron
► Particle charged negatively (-1) and is 1/1836th the size of a proton. They are outside the atom and in constant motion around it. Chemical reaction are, grosso modo, an exchange of electrons.
Proton
► Particle in the nucleus with a positive charge (+1).
Neutron

► A non-charged particle in the nucleus with the same mass of a proton.

Some useful references:

Unit conversion calculator: http://www.chemicool.com/cgi-bin/unit.pl
Basic graphs: http://www.chemicool.com/graph.html
 
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Sodapop

CHF Hall of Fame
May 2009
76
10
Montréal, QC
I. Ideal gas law explanation
Three important factors influence the state of a gas: its pressure, its volume and its temperature. This law is a good approximation to the many possible behaviors of gases under certain restricted conditions. The form of the equation is the following:

pV = nRT
p = pressure of the gas
V = volume of the gas
n = amount of substance (most of the time expressed in moles)
R = ideal gas constant (0.08206 L atm mol^(-1) K^(-1))
T = absolute temperature (usually in Kelvin, where 273 K = 0°C)

As we all know, a formula has to posses the basic equilibrium found in any equality. In this case, the pressure of the gas multiplied by the volume of the gas gives us the numbers of moles multiplied by the constant R and the temperature. Simple algebra can be used to find the unknown or missing variable in our equation.

Please note: Always remember to convert your volume into L (litres), your temperature into K (Kelvin) and your atomspherical pressure into atmospheres (atm). Altough it is possible to solve with kPa units, this reduced form remains the simpliest and the easiest to use. Here is an example:

What is the volume (in L) of 1 mole of an ideal gas at standard temperature (273 K) and at a pressure of 1 atm?

pV = nRT

V = nRT / P

V = (1mol x 0.08206 L atm mol^(-1) K^(-1) x 273K) / 1 atm

Canceling the atms, we have:

V = (1mol x 0.08206 L mol^(-1) K^(-1) x 273K) / 1

Canceling the mols and the K [(mol^(-1) K^(-1)) x (1mol x 273K)]:

V = (1 x 0.08206 L x 273) / 1

V = (1 x 0.08206 L x 273)

V = (0.08206 L x 273)

V = 22.4 L
 
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Sodapop

CHF Hall of Fame
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Montréal, QC
II. Lewis structure
The Lewis structure represents, in a small scheme, the total number of valence electrons by adding small dots around the element symbol. Non-valence electrons are not represented in this structure. The octet rule says that molecules with eight electrons on their valence shell (last shell) will acquire stability.

Once the total number of available electrons has been determined, electrons must be placed into the structure. They should be placed initially as lone pairs: one pair of dots for each pair of electrons available. Lone pairs should initially be placed on outer atoms (other than hydrogen) until each outer atom has eight electrons in bonding pairs and lone pairs; extra lone pairs may then be placed on the central atom. When in doubt, lone pairs should be placed on more electronegative atoms first.

Advanced studies of the Lewis structure lets us place and study the bonds between the molecules.

The Lewis structure for the Neon molecule is the following:
 
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Sodapop

CHF Hall of Fame
May 2009
76
10
Montréal, QC
III. Periodic table
The groups are the vertical columns found in the periodic table. They are the most important classification of the periodic table: properties of elements in a same group usually share similarities.

* Group 1 (IA,IA): the alkali metals or lithium family
* Group 2 (IIA,IIA): the alkaline earth metals or beryllium family
* Group 3 (IIIA,IIIB): the scandium family
* Group 4 (IVA,IVB): the titanium family
* Group 5 (VA,VB): the vanadium family
* Group 6 (VIA,VIB): the chromium family
* Group 7 (VIIA,VIIB): the manganese family
* Group 8 (VIII, VIIIB): the iron family
* Group 9 (VIII, VIIIB): the cobalt family
* Group 10 (VIII, VIIIB): the nickel family
* Group 11 (IB,IB): the coinage metals or copper family
* Group 12 (IIB,IIB): the zinc family
* Group 13 (IIIB,IIIA): the boron family
* Group 14 (IVB,IVA): the carbon family
* Group 15 (VB,VA): the pnictogens or nitrogen family
* Group 16 (VIB,VIA): the chalcogens or oxygen family
* Group 17 (VIIB,VIIA): the halogens or fluorine family
* Group 18 (Group 0): the helium family/neon family; for the first six periods, these are the noble gases

The periods are the horizontal rows of the periodic table. Although they have no specific names, they are also used for classification in the periodic table. Two elements facing each other in the same period have ±1 number of protons. There is a total of seven periods, excluding the Lanthanide series and the Actinide series.



*CURRENT ATTACHED IMAGE IS NOT WORKING. IT WILL BE UPDATED SOON.
 
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Sodapop

CHF Hall of Fame
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Montréal, QC
IV. Potential of Hydrogen (pH)
The pH is the measurement of basicity/acidity in a solution. The following scale represents the different values and gives us common examples:

Solutions with a pH under 7 are said to be acid while solution with a pH over 7 are said to be basic. A basic solution can be as dangerous if not more than an acid solution. Also, take note that the temperature of a solution also slightly affects its pH.

When an acid gets dissolved into water, the pH of the solution drops under 7, depending on the pH of the used acid. Stronger acids drops the pH more quickly, while stronger bases raises the pH more quickly. That's where the concept of neutralization takes life: you need a strong base to neutralize (bring back to a pH of 7) a strong acid. When a solution is successfully neutralized, it creates water (H20) and salt (NaCl). The balanced equation of a neutralization is the following:
HCl [acid] + Na(OH) [base] -> H2O [water] + NaCl [salt].
 
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Dec 2009
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Interactive chemistry site

Hello everybody!
I launched a new chemistry site to help students. You can download the study material from this site freely.
http://www.adichemadi.com

Aditya
 

Sodapop

CHF Hall of Fame
May 2009
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Montréal, QC
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