Stoichiometry Chapter 9

Stoichiometry Composition stoichiometry: deals with mass relationships in compounds Reaction stoichiometry: involves mass relationships between reactants & products in a chemical reaction

Vocabulary Mole ratio: a conversion factor that relates the amounts in moles of any two substances involved in a reaction Found in balanced equation Molar mass: mass in grams of one mole of a substance Found on periodic table

IMPORTANT! The first step in all stoichiometry problems is to balance the chemical equation!

PROBLEM In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation: CO2 + LiOH  Li2CO3 + H2O How many moles of LiOH are required to react with 20 mol of CO2, the average amount exhaled by a person each day?

PROBLEM Tin (II) fluoride is used in some toothpastes PROBLEM Tin (II) fluoride is used in some toothpastes. It is made according to the following equation: Sn + HF  SnF2 + H2 How many grams of SnF2 are produced from the reaction of 30.00g of HF with Sn?

In the lab, a reaction is rarely carried out with exactly the required amounts of each of the reactants. Excess reactant Not completely used up Produces largest amount of product Limiting reactant Completely used up first Limits the amount of product that can form Produces the smallest amount of product

PROBLEM Silicon dioxide (quartz) is usually quite unreactive but reacts readily with hydrogen fluoride according to the following reaction: SiO2 + HF  SiF4 + H2O If 2.0 mol of HF are exposed to 4.5 mol of SiO2, which is the limiting reactant?

The black oxide of iron occurs in nature as the mineral magnetite The black oxide of iron occurs in nature as the mineral magnetite. This substance can also be made in the lab by the reaction between red-hot iron & steam. Fe + H2O  Fe3O4 + H2 When 36.0g of H2O is mixed with 167g of Fe, which is the limiting reactant? What mass in grams of black iron oxide is produced? What mass in grams of excess reactant remains when the reaction is completed?

Percent Yield Theoretical yield: maximum amount of product that can be produced from a given amount of reactant What you expect to get from calculations Actual yield: measured amount of product obtained from a reaction What you get if the reaction is actually ran Percent yield= Actual yield x 100 Theoretical yield

PROBLEM Chlorobenzene is used in the production of many important chemicals, such as aspirin, dyes, & disinfectants. The industrial method of preparing chlorobenzene is represented in the following equation: C6H6 + Cl2  C6H5Cl + HCl When 36.8g of C6H6 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8g. What is the percent yield of C6H5Cl?

PROBLEM Methanol can be produced through the following reaction: CO + H2  CH3OH If 75.0g of CO reacts to produce 68.4g CH3OH, what is the percent yield of CH3OH?