We are into Chapter 4..... So add away.... Only a week to get your 5 pity points!

stoichiometry = a calculation of amount of reactants used or products formed during a reaction

4Fe + 3O2 --> 2Fe2O3
the coefficients used to balance the above equation represent the # of moles.

Steps for Solving Stoich Problems:

1. balance the equation.
2. read the problem, see what you are given, and see what you are trying to find.
3. whatever info is given will be the starting point. make this info the numerator and divide it by 1.
4. convert that given info into moles (if the given was not moles to begin with). use the molar mass (from the periodic table), the density (check if it is at STP or not), or the atom/mole ratio (6.02 x 10^23).
5. from the number of moles of the given information, use the mole-to-mole ratio from the balanced equation to figure out the number of moles of what you are trying to find.
   
6. if you are simply solving for the number of moles, stop at this point. if the problem asks for mass, volume, number of molecules/atoms, etc., convert the number of moles to whatever it is you need using appropriate conversion factors.
   

Chemical Equations:

• Reactants are on the left of the arrow (substances combined in the reaction)
• Products are on the right of the arrow (substances produced in the reaction)
• The physical states of reactants and products:
  • (s) = solid
  • (g) = gas
  • (l) = liquid
  • (aq) = aqueous solution (a substance dissolved in water)<-- Does it have to be water? yes an aqueous solution is a solution in which water is the solvent. How about any other polar solvent?
    

• Law of conservation-matter can be neither created nor destroyed (If you start with a certain mass of reactants, and the reaction completely converts reactants to products, you must end up with the same mass for the products)
  
• Stoichiometry- the relationship between the quantities of chemical reactants and products
• Stoichiometric coefficients- the coefficients in a balanced equation
• Stoichiometric factor- a mole ratio based on the coefficients in the balanced equation
  
• You must always begin with a balanced equation before carrying out a stoichiometry equation.
• In all combustion (burning) reactions, some or all of the reactants end up as oxides. When the reactant is a hydrocarbon, the products are always carbon dioxide and water.

When balancing chemical equations...

• Subscripts in the formulas cannot be changed. Only work with coefficients.
  

For reactions involving organic compounds, balance the carbon (C) atoms first, then hydrogen (H), then oxygen (O). [okay mr. craddock I just want to clarify that I did do this during our battle...for some reason I thought it was a different order when you asked me...ok just had to put that out there.]

• Always check to make sure that the number of atoms of each element are equal on both sides.

Determining formula of hydrocarbon through Stoich Example:

1. If given the mass of carbon dioxide and water as products, convert each mass to moles
2. find the number of moles of each carbon and hydrogen required to produce given products
   • remember there are 2 moles of hydrogen per mole of water
   • there is 1 mole of carbon per mole of carbon dioxide
3. do a ratio between carbon and hydrogen to determine formula of hydrocarbon

Percent Yield (specifies how much of the theoretical yield was obtained)

Percent yield = ( actual yield / theoretical yield ) x 100

• Theoretical yield- the maximum quantity of product calculated from a chemical reaction
• Actual yield- quantity of material that is actually obtained in the lab (usually less than the theoretical yield)

Material balance (also known as a mass balance; used with the conservation of mass law to determine if unknown mass has been added/lost during known mass flow)

(mass of alum obtained + mass of alum in solution)/theoretical mass of alum x 100

• for our potassium aluminum sulfate lab, we used a given table to determine the mass of alum in solution