Stoichiometry is a big word that simply means "the study of quantities in chemical reactions". Using the basic tools we have developed in previous chapters, we will be able to solve problems relating to these quantities. 11.1: General Stoichiometry We have used balanced equations to set up ratios, in terms of moles of materials, that we can use as conversion factors to answer stoichiometric questions—such as how many moles of substance A react with so many moles of reactant B. We can extend this technique even further. Recall that we can relate a molar amount to a mass amount using molar mass. We can use that relation to answer stoichiometry questions in terms of the masses of a particular substance, in addition to moles. 11.1.1: Mass Stoichiometry 11.1.2: Solution Stoichiometry 11.1.3: Stoichiometry and the Ideal Gas Law 11.1.4: Gas Stoichiometry at STP 11.1.5: Acid–Base Titration 11.2: Limiting Reactant In all the examples discussed thus far, the reactants were assumed to be present in stoichiometric quantities, with none of the reactants left over at the end of the reaction. Often reactants are present in mole ratios that are not the same as the ratio of the coefficients in the balanced chemical equation. As a result, one or more of them will not be used up completely, but will be left over when the reaction is completed. 11.3: Theoretical Yield, and Percent Yield Chemists need a measurement that indicates how successful a reaction has been. This measurement is called the percent yield. The limiting reagent is that reactant that produces the least amount of product. Mass-mass calculations can determine how much product is produced and how much of the other reactants remain. 11.4: Enthalpy Change is a Measure of the Heat Evolved or Absorbed A chemical reaction or physical change is endothermic if heat is absorbed by the system from the surroundings. In the course of an endothermic process, the system gains heat from the surroundings and so the temperature of the surroundings decreases. The quantity of heat for a process is represented by the letter q. The sign of q for an endothermic process is positive because the system is gaining heat. A chemical reaction or physical change is exothermic if heat is released by the system. 11.E: Stoichiometry Applications (Exercises) These are exercises and select solutions to company Chapter 11. Template:HideTOC