Unit 8

Introduction

• stoichiometry is using quantitative relationships between reactants and products in a chemical reaction, such as conservation of mass, balancing equations, moles, and mole ratios

• used to predict theoretical amounts of products

• First, you must write a balanced equation, then determine the number of moles of each reactant used, then use the mole ratio to find the theoretical yield, and finally calculate the percent yield

• percent yield = actual yield/theoretical yield x 100

Limiting Reactant

• If given both reactants for an equation, you must find which one is of lesser quantity

• Make sure you have a balanced equation, convert grams of reactants to moles

• not all reactants will be used up in a reaction

• limiting = gets used up first

• excess = left over

• three methods of figuring out limiting reactant

• method 1: compare actual mole ratio of reactants to the required mole ratio of reactants (from balanced equation)

• method 2: start with moles of one reactant and figure out how many moles of the second reactant are needed. Compare to actual amount of moles of second reactant

• method 3: determine how much product would be formed using each reactant as a starting point. Whichever reactant produces less product is the limiting reactant