Chapter 7: Mass Stoichiometry Flashcards
formula mass
the sum of the atomic masses of all the atoms in a chemical formula
aka formula weight, molecular mass, or molecular weight
atomic mass unit (amu)
a standard unit of mass used to measure the mass of atoms, molecules, and subatomic particles; equal to 1/12 of the mass of a carbon-12 atom
percent composition
the percentage by mass of each element in a compound; equal to the mass of one element divided by the mass of the entire compound x 100%
mole
a quantity consisting of 6.02 x 10^23 units
Avogadro’s number
the number of particles in a mole - 6.02 x 10^23
mole concept
the mole is an amount similar to familar units such like a pair or dozen; it provides a specific measure of the number of atoms or molecules in a bulk sample of matter
the mole concept allows us to express the atomic mass in
grams; we can say that the mass of an element is grams per mole (lab scale)
molar mass
mass expressed in grams per mole
when we write the conversion factor, the unit we wish to cancel goes on the
bottom; the one we wish to keep goes on the top
to convert between grams and moles, we use
molar mass
to convert between moles and particles, we use
Avogadro’s number
to convert between moles of two different substances, we use
the mole ratio from the balanced equation
mole ratio
the ratio of the amounts (in moles) of any two substances involved in a chemical reaction, as seen from the coefficients of the balanced chemical equation
stoichiometry problem
a problem that relates the amount of one reagent or product to another in a chemical reaction using a balanced equation
excess reagent
reactants that are not used up when the reaction is finished
limiting reagent
the compound that is consumed first; determines the amount of product that can form in a reaction
to find the limiting reagent, we calculate
the amount of product that each starting material can product; the starting material that can produce the least amount of product is the limiting reagent
to find leftovers in a stoichiometry problem, we
subtract what we used from our starting material
theoretical yield
the amount of product that can form in a chemical reaction based on the balanced equation and the amount of starting materials present
we find the theoretical yield by
identifying the limiting reactant and using the mole ratio to determine the moles of product that can be formed from it
actual yield
the amount of product that is actually produced when a chemical reaction is carried out
percent yield
a measure of the efficiency of a reaction; it compares the actual yield and the theoretical yield
percent yield formula
actual yield / theoretical yield x 100%