Stoichiometry is the culmination of many concepts in chemistry. It integrates dimensional analysis, moles and molar mass, molar volumes of gases, concentrations and balanced chemical equations to use information about one species in a reaction to determine information about another species in the same reaction.
Review
Chemical equations are used to relate reactants and products in a chemical reaction. Dimensional analysis is a technique that uses ratios of equivalents to convert units. The KUDOS method is a method for solving word problems. Molarity is a concentration unit showing the ratio of moles of solute to volume of solution.
Mole-Mole problems
The balanced equation gives the ratio of moles of each species in the reaction. The balanced equation is used to determine mole ratios for use in dimensional analysis when converting from the moles of one species to the moles of another. Moles is the only unit that may be used to convert from one chemical to another—mass or volume cannot be used to convert between chemicals, just within the same one.
Mole-Mass & Mass-Mass problems
Molar mass is an equivalent between the mass in grams and moles of a substance. The molar mass is used to convert between moles of a substance and mass in a stoichiometry problem.
Mole-Volume problems for solutions
The concentration, in molarity, of a solution gives the equivalent for moles of the solute and liters of solution. The molarity can be used to convert between moles and volume of a solution in stoichiometry problems.
Mole-Volume problems for gases
The volume of 1 mole of any gas at standard temperature and pressure is 22.4 L. The molar volume of a gas can be used to convert between moles and volume of a gas at STP in stoichiometry problems. If a problem asks for the volume at non-standard temperature or pressure, find the STP volume using stoichiometry and then use the appropriate gas law to convert to the desired temperature or pressure.
