Chemistry-Unit 10: Stoichiometry

Stoichiometry

The study of quantitative relationships between the amounts of reactants used and products formed by chemical reaction; is based on the law of conservation of mass.

Five steps to solving stoichiometry problems

1) Write the complete balanced equation.

2) Identify want and given.

3) Convert given to moles (if not already given in moles).

4) Convert given moles to want moles.

5) Convert want moles to want units (if needed...once you have the desired units, STOP).

actual yield

the amount of product that forms when a reaction is carried out in the laboratory

theoretical yield

the maximum amount of product that could be formed (in theory) from given amounts of reactants

limiting reactant (reagent)

the reactant that is completely consumed when a reaction is run to completion

excess reactant (reagent)

a reagent present in a quantity that is more than sufficient to react with a limiting reagent; any reactant that remains after the limiting reagent is used up in a chemical reaction

percent yield

the ratio of the actual yield to the theoretical yield expressed as a percent

% Yield = (actual yield/theoretical yield) * 100

mole ratio

in a balanced equation, the ratio between the numbers of moles of any two substances

significant figures

a prescribed decimal place that determines the amount of rounding off to be done based on the precision of the measurement

mole conversions

1 mol of an element=molar mass; 1 mol=6.02*10^23 atoms/molecules; 1 mol of compound=molar mass

mass-mass problem

Stoichiometric problem in which the mass of one substance is determined from the mass of another substance in the reaction; solved by using the molar ratio indicated by the balanced chemical equation

mass-mole problem

Stoichiometric problem in which the mass of the given substance is converted into moles by use of the molar mass of that substance from the periodic table. Then, the moles of the given substance are converted into moles of the unknown by using the mole ratio from the balanced chemical equation.

mass-energy problem

A problem in which the amount of energy is absorbed or released during a reaction can be calculated from the mass of materials

Law of Conservation of Mass

the law that states that mass cannot be created or destroyed in ordinary chemical and physical changes

Template for solving stoichiometric problems

(G)grams (G)1 mole/(G) molar mass (in grams) (W) moles/(G) moles * (W) molar mass (in grams)/(W) 1 mole

G= Given

W= Want