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Chemistry: Stoichiometry

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Chemistry: Stoichiometry
« on: September 08, 2014, 10:25:03 AM »
Stoichiometry Stoichiometry deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations   among quantities of reactants and products typically form a ratio of   whole numbers. For example, in a reaction that forms ammonia (NH3), exactly one molecule of nitrogen (N2) reacts with three molecules of hydrogen (H2) to produce two molecules of NH3
N2 + 3H2 → 2NH3
Stoichiometry can be used to calculate quantities such as the amount of products (in mass, moles, volume, etc.) that can be produced with given reactants and percent yield (the percentage of the given reactant that is made into the product). Stoichiometry calculations can predict how elements and components diluted in a standard solution react in experimental conditions. Stoichiometry is founded on the law of conservation of mass: the mass of the reactants equals the mass of the products.
 The Periodic Table and Charges:
Group
 (Charge) [/t][/t]
[/t]
1
 (+1)
2
 (+2)
Transition
 metals
3
 (+3)
4
 (±4)
5
 (-3)
6
 (-2)
7
 (-1)
Ions
 present
Li+
 Na+
 K+
Be2+
 Mg2+
 Ca2+
 Ba2+
Cu2+ / Cu+
 Fe2+ / Fe3+
 Zn2+
 Ag+
Al3+
C
 Si
 Pb2+
N3-
 P3-
O2-
 S2-
F-
 Cl-
 Br-
 I-
    Compound Ions: They are like molecules but with a charge on them:
 
Oxidation State[/t][/t]
[/t]
Name
Symbol
+1
Ammonium Ion
NH4+
-1
Hydroxide Ion
 Nitrate Ion
 Nitrite Ion
 Manganate(VII) Oxide Ion
 Hydrogen Carbonate Ion
OH-
 NO3-
 NO2-
 MnO4-
 HCO3-
-2
Carbonate Ion
 Sulfate Ion
 Sulfite Ion
 Dichromate (Vi) Ion
CO32-
 SO42-
 SO32-
 Cr2O72-
-3
Phosphate Ion
 Phostphite Ion
PO43-
 PO33-
    Acids and Their Formulae:
Acid[/t][/t]
[/t]
Formula
Carbonic Acid
H2CO3
Hydrochloric Acid
HCl
Nitric Acid
HNO3
Phosphoric Acid
H3PO4
Sulfuric Acid
H2SO4
   
 Chemical Changes:  When chemical reactions take place, a certain change is certain. This change could be in color, energy or something like bubbles or a  precipitate formation.
 Color Change in Reactions:  When iron, which is grey, reacts with sulfur, which is  yellow, a black solid, iron sulfide is formed. The color changed from grey and yellow to black.
 
Iron[/t][/t]
[/t]
+
Sulpher
Iron Sulfide
(grey fillings)
(yellow powder)
(black solid)
  Energy Change in Reactions:  Energy is not necessarily heat, there are several forms of  energy like Light and sound energy too.
When magnesium reacts with oxygen in air to make a  combustion reaction, it burns with a very bright flame forming magnesium oxide. This bright flame is light energy which indicates a reaction took place.
Some reactions also release energy in form of sound like  explosive reactions.
 Effervescence in Reactions:  In some reactions, bubbles are formed rapidly. Those bubbles are indication that a gas was formed which is a new substance, this means a  reaction took place.
When calcium carbonate reacts with hydrochloric acid, carbon  dioxide gas is released in bubbles.
CaCO3 + 2HCl → CaCl2 + H2O + CO2
Precipitation in Reactions:  When two solutions react together, sometimes one of the products is an insoluble solid called precipitate. When silver nitrate solution  reacts with a potassium chloride solution, white insoluble silver chloride is  formed which is a precipitate.
AgNO3 + KCl → AgCl + KNO3
Writing and Balancing Equations: Chemical reactions are always represented by chemical  equations to show the reactants and the products. There are two types of  chemical equations. These are word equations and symbolic equations.
For example if we want to represent the reaction between sodium and chlorine which produces sodium chloride as a word equation it will be like  this:
Sodium + Chlorine → Sodium Chloride
If we want to represent the same reaction by a symbolic  equation it will be like this:
Na + Cl2 → NaCl
The above symbolic equation however, is not chemically  accurate. This is why chemists prefer to use what’s called a balanced symbolic  equation. In this type of equation, we make sure that the number of atoms of each element in the reactants is the same in the products. If you look at the  equation above you will find that we have one Na atom in the reactants and one  Na+ ion in the product, but we have 2 Cl atoms in the reactants and only one Cl  ion in the product. This is why this equation needs to be balanced as follows:
2Na + Cl2 → 2NaCl
Types of Chemical Reactions: Combustion (oxidation) Reactions:  These are reactions between metals and oxygen or the  oxidation of any other element.
 
2Mg[/t][/t]
[/t]
+
O2
2Li2O
(Magnesium)
(Oxygen)
(Magnesium Oxide)
  Hydration Reactions:  These are reactions between metals and water forming a metal hydroxide and hydrogen gas. It could also be a reaction between a salt and  water forming a hydrated salt.
 
2Na[/t][/t]
[/t]
+
2H2O
2NaOH
+
H2
(Sodium)
(Water)
(Sodium Hydroxide)
(Hydrogen)
   
 
CuSO4[/t][/t]
[/t]
+
5H2O
CuSO4.5H2O
(Copper Sulfate)
(Water)
(Hydrated Copper Sulfate)
  Displacement Reactions:  These are the reactions in which the more reactive metal displaces the less reactive positive ion. In the following reaction, sodium  displaces Hydrogen ion from the hydrochloric acid because sodium is more reactive.  The products are sodium chloride and hydrogen gas.
 
2Na[/t][/t]
[/t]
+
2HCl
2NaCl
+
H2
(Sodium)
(Hydrochloric Acid)
(Sodium Chloride)
(Hydrogen)
  Neutralization Reactions:  These are reactions between an alkaline compound or and  alkali and an acidic compound or an acid forming a salt, water and sometimes carbon dioxide.
In the following reaction sodium hydroxide is a base which reacts with sulfuric acid. Neutralization takes place producing a salt called  sodium sulfate and water.
 
2NaOH[/t][/t]
[/t]
+
H2SO4
Na2SO4
+
2H2O
(Sodium Hydroxide)
(Sulfuric Acid)
(Sodium Sulfate)
(Water)
  In the following reaction calcium carbonate which is a basic compound reacts with nitric acid forming a salt called calcium nitrate, water  and carbon dioxide.
 
CaCO3[/t][/t]
[/t]
+
2HNO3
Ca(NO3)2
+
H2O
+
CO2
(Calcium Carbonate)
(Nitric Acid)
(Calcium Nitrate)
(Water)
(Carbon dioxide)
[/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table][/td][/tr][/table]

 

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