AP Chemistry Zumdahl Notes, 9th ed. A Brief Collection of notes, Chapter 3 Feel free to open these files and annotate as you feel the need…this is for your success.

Stoichiometry Counting by weighing…do you really think you can count atoms? Atomic masses AMU: one-twelfth of a carbon-12 atom Atomic mass: weighted avg. of naturally occurring isotopes The Mole: using Avogadro’s number Think “just another conversion” Molar Mass: appropriate calculation using subscripts as multipliers Percent Composition of Compounds Mass percent: remember must total 100% Mass component/mass total x 100 = %component Determination of Formula: assume 100 g of material, convert to g, divide by appropriate atomic masses to find moles, divide all by smallest to get ratio. This will give empirical formula, which may or may not be the molecular formula

Stoichiometry Chemical Equations Balancing Chemical Equations Reactants produce products Balancing Chemical Equations Can change coefficients in front of reactants and products, but cannot change subscripts, as this changes these compounds Look for elements with multiples on different sides…must find coefficients such that they will be equal on both sides If polyatomic ions are on both sides, keep them intact…makes your counting that much easier

Stoichiometry Amounts of Reactants and Products Before you can solve virtually any stoichiometry problem, you must take what information you are given and convert it into moles; then, find the appropriate mole ratio for what you need, then modify your output into the format needed Limiting Reactant: which one can determine how far your reaction if allowed to progress? Again, need to convert all info into moles, then determine, using DA/factor label, which one is limiting; now, base all calculations on this, as it controls outputs; can be determined with either reactants or products, just means that your approach is from a different direction

Stoichiometry Yield Calculations: based upon limiting reactant/s, this is what could be produced if reaction goes 100% (theoretical yield). Percent yield = (actual yield)/(theoretical yield) x100% Reality check…cannot be over 100%  I think one of the things to always remember about the different stoichiometric calculations is that you should be able to back-track and show your pathway to your answer. It is always a series of logical steps.