Zumdahl- Chemistry (5th ed.) Chapter 3 Stoichiometry Zumdahl- Chemistry (5th ed.) Last revision Fall 2006

The Mole The mole is a quantity of matter. It is a count of how many atoms are in a sample. 1 dozen = 12 eggs is like 1 mole = 6.02x1023 particles Converting between moles and particles is just like doing a dimensional analysis problem. Particles is a generic term used to stand for: atoms, molecules, formula units, ions, electrons, etc.

Molar Mass A substance’s molar mass (molecular weight) is the mass in grams of one mole of the compound. It turns out the molar mass is equivalent to the average atomic mass. Average atomic mass = 12.011 amu= 12.011g/mol  12.011g = 1 mole of Carbon C 6 12.011 Formula mass: the mass of all the atoms in a formula

Percent Composition Mass percent of an element: For iron in iron (III) oxide, (Fe2O3)

The equation is balanced. Stoichiometry allows chemists to calculate quantities of different substances in the reaction using their coefficients. C2H5OH + 3O2  2CO2 + 3H2O The equation is balanced. 1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water The relationship between the substances is called the molar ratio.

Limiting Reactant You can make cookies until you run out of one of the ingredients. Once this family runs out of sugar, they will stop making cookies (at least any cookies you would want to eat). 4 sticks of butter 7 cups of sugar 30 cups of Milk 24 cups of flour 20 eggs Cookie Recipe: ½ stick of butter 2 eggs 1 cup sugar 1 cup mikk 3 cups flour

Theoretical yield vs. actual yield The theoretical yield is the maximum amount of product that can be made by the limiting reagent. In other words it’s the amount of product possible as calculated through the stoichiometry problem. This is different from the actual yield, which is the amount one actually produces and measures in the lab.

Percent Yield Actual Yield Theoretical Yield Percent Yield = x 100 One finds the percent yield by comparing the amount actually obtained (actual yield) to the amount it was possible to make (theoretical yield). Actual Yield Theoretical Yield Percent Yield = x 100