Feb.8/2011:Limiting Reactants (Brian)

In chemical reactions, usually one chemical gets used up before the other
-The chemical used up first is called the limiting reactant
-Once it is used up the reaction stops
-L.R determines the quantity of products formed
-To find the L.R assume one reactant is used up, determine how
  much of this reactant is required

example:
Find the L.R when 2.8mol of H2 reacts with 1.25mol of O2
2H2+O2 -----> 2H2O
2.8 x 1 = 1.4 mol L.R or 1.25mol x 2 = 2.5
         2                                      1

Feb.8/2011:Percent Yield (Brian)

-The theoretical yield of a reaction is the amount of products that should be formed
-The actual amount depends on the experiment
-The percent yield is like a measure of success

* % yield = Actual      multiplied by 100
                Theoretical  example:
in a double replacement reaction silver nitrate is reacted with barium sulphate. If 2.0mol of silver nitrate react and 468g of silver sulphate are produced.
-determine the theoretical yield of Ag2SO4
-determine the percent yield
2AgNO3+BaSO4 ----> Ba(NO3)2+Ag2SO42.0mol x 1 x 311.9g = 311.9g                          468g x 100 = 150%
               2    1mol                                          311.9g

February 2, 2011: Other Conversions, Volume and Heat (Angelo)

Volume and Heat:
- volume  at STP can be found using the conversion factor 22.4 L/mol (litres/mol)
- heat can be included as a separate term in chemical reactions (this is called ENTHALPHY)
- reactions that release heat are exothermic
- reactions that absorb heat are endothermic
- both can be used in stoichiometry

EXAMPLES:


1. If 5.0 grams of Potassium chlorate decompose according to the reaction below, what volume of Oxygen gas (at STP) is produced?

Create your balanced equation: 2KClO3 -----> 2KCl + 3O2
Create your equation: 5.0 grams * (1 mol / 122.5 g.) * (3 mols / 2 mols) * (22.4 L. / 1 mol) = ?
Calculate: 5.0 grams * (1 mol / 122.5 g.) * (3 mols / 2 mols) * (22.4 L. / 1 mol) = 1.4 L.

January 27: Mass to Mass Conversions (Angelo)

Mass to Mass Conversions:
- mass to mass problems involved one additional conversion
- this chart is a visual example of how to perform mass to mass conversions
GRAMS OF A -------> MOLES OF A -------> MOLES OF B -------> GRAMS OF B


EXAMPLES:


1. Lead (IV) Nitrate reacts with 5.0 grams of Potassium Iodide. How many grams of Lead (IV) nitrate are required for a complete reaction?

Create your balanced equation: Pb(NO3)4 + 4KI -----> 4KNO3 + PbI4
Create your equation: 5.0 grams (KI) * (1 mol / 166 g. (KI)) * (1 mol (Pb(NO3)4) / 4 mols (KI)) * (455.2 g. (Pb(NO3)4) / 1 mol) = ?
Calculate: 5.0 grams (KI) * (1 mol / 166 g. (KI)) * (1 mol (Pb(NO3)4) / 4 mols (KI)) * (455.2 g. (Pb(NO3)4) / 1 mol) = 3.4 grams (Pb(NO3)4)

January 25, 2011: Moles to Mass and Mass to Moles (Angelo)

Moles to Mass and Mass to Moles:
- some questions will give you an amount of moles and ask you to determine the mass
- converting moles to mass only requires one additional step

EXAMPLE:


1. How many grams of Bauxite (Al2O3) are required to produce 3.5 mols of pure Aluminum.

Create your balanced equation: 2NO3 -----> 4Al + 3O2
Create your equation: 3.5 mol (Al) * (2 mols (Al2O3) / 4 mols (Al)) * (102 grams (Al2O3) / 1 mol (Al2O3)) = ?
Calculate: 3.5 mol (Al) * (2 mols (Al2O3) / 4 mols (Al)) * (102 grams (Al2O3) / 1 mol (Al2O3)) = 1.8 x 10^2 grams


2. How many moles of Lead (II) Nitrate are consumed when 4.5 grams of Sodium Sulphide completely react?

Create your balanced equation: Pb(NO3)2 + Na2S -----> PbS + 2NaNO3
Create your equation: 4.5 grams * (1 mol / 78.1 g.) * (1 mol / 1 mol) = ?
Calculate: 4.5 grams * (1 mol / 78.1 g.) * (1 mol / 1 mol) = 0.058 grams

January 21, 2011: Mole to Mole Conversions (Angelo)

Mole to Mole Conversions:
- coefficients in balanced equations tell us the number of moles reacted or produced
- they can also be used as conversion factor:
3X + Y = 2Z
- WHAT YOU NEED over WHAT YOU HAVE


EXAMPLES:


1. If 0.20 mol of Methane are consumed in a combustion reaction, how many moles of CO2 are produced?

Create your balanced equation: CH4 + 2O2 -----> CO2 + H2O
Create your equation:  0.20 mol (CH4 ) * (1 mol (CO2) / 1 mol (CH4)) = ?
Calculate: 0.20 mol (CH4 ) * 1 mol (CO2) / (1 mol (CH4) = 0.2 mol (CH4))

2. When 2.0 mol of Copper (II) react with Iron (II) Chloride, how many moles of iron should be producted?

Create your balanced equation: Cu + FeCl2 -----> CuCl2 + Fe
Create your equation: 2.0 mol * (1 mol / 1 mol) = ?
Calculate: 2.0 mol

NOTE: When you are comfortable, you may remove what type of element, compound, etc. you are using.

Jan 18th, 2010 - Stoichiometry (Zac)

-Stoichiometry is a branch of chemistry that deals with the quantitive analysis of chemical  reactions
-It is a generalization of mole conversions to chemical reaction
-Understanding the 6 types of chemical reactions is the foundation of stoichiometry
SYNTHESIS
A + B = AB
-Usually elements that form compounds
-The formation reactions must be balanced
eg.  2Al + 3F2 = 2AlF3
eg.  2SO2 + O2 = 2SO3
DECOMPOSITION
AB = A + B
-Reverse of Synthesis
-Always assume that the compounds decompose into single elements during the reaction
eg.  Mn(C2O4)2 = Mn + 4C +4O2
eg.  2C12H22O11 = 24C + 22H2 + 11O2
SINGLE REPLACEMENT
A + BC = B + AC
eg. 3Mg + 2(Al(NO3)3 = 2Al + 3Mg(NO3)2
DOUBLE REPLACEMENT
AB + CD = AD + BC
eg. 2Al(NO3)3 +3SrCO3 = Al2(CO3)3 + Sr(NO3)3
eg. AgNO3 + NaCl = NaNO3 + AgCl
NEUTRALIZATION
-A reaction between an acid and a base (acids usually include hydrogen & bases have hydroxide)
eg. 3Ca(OH)2 +2H3PO4 = Ca3(PO4)2 + 6HOH
COMBUSTION
-Reactions of something (usually hydrocarbon) with air
-Hydrocarbon compustion always produces carbon dioxide and water.
eg. CH4 + 4O2 = CO2 + 2H2O
eg. 4Al + 3O2 = 2Al2O3