Calculating Quantities in Reactions Mass-to-mass problems Stoichiometry Table of Contents Calculating Quantities in Reactions Mass-to-mass problems Limiting Reactants and Percentage Yield

What is the percentage composition of NH4I? Calculating Quantities in Reactions Bellringer What is the percentage composition of NH4I? Molar mass= 14 + 4x(1) + 127= 145 g/mol N  14/145*100 = 9.6 % H  4/145*100 = 2.8 % I  127/145*100 = 87.6

Balanced Equations Show Proportions Calculating Quantities in Reactions Balanced Equations Show Proportions The proportions of the ingredients in a muffin recipe let you adjust the amounts to make enough muffins even if you do not have balanced amounts initially. In a balanced chemical equation coefficients show the proportions of the reactants and products.

Balanced Equations Show Proportions Calculating Quantities in Reactions Balanced Equations Show Proportions 2H2 + O2  2H2O The coefficients show that two molecules of hydrogen react with one molecule of oxygen and form two molecules of water. Calculations involving chemical reactions use the proportions from balanced chemical equations to find the quantity of reactants and products involved.

Balanced Equations Show Proportions Calculating Quantities in Reactions Balanced Equations Show Proportions For each problem in this section, assume that there is more than enough of all other reactants to completely react with the reactant given. Also assume that every reaction happens perfectly, so that no product is lost during collection.

Calculating Quantities in Reactions Relative Amounts in Equations Can Be Expressed in Moles The branch of chemistry that deals with quantities of substances in chemical reactions is known as stoichiometry.

Calculating Quantities in Reactions Relative Amounts in Equations Can Be Expressed in Moles The coefficients in a balanced equation also represent the moles of each substance. For example, the equation below shows that 2 mol H2 react with 1 mol O2 to form 2 mol H2O. 2H2 + O2  2H2O

Using Mole Ratios Sample Problem A N2 + 3H2  2NH3 Calculating Quantities in Reactions Using Mole Ratios Sample Problem A A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction. Consider the reaction for the commercial preparation of ammonia. N2 + 3H2  2NH3 How many moles of hydrogen are needed to prepare 312 moles of ammonia?

N2 + 3H2  2NH3 Using Mole Ratios Sample Problem A Solution Calculating Quantities in Reactions Using Mole Ratios Sample Problem A Solution amount of NH3 = 312 mol amount of H2 = ? mol 3 mol H2 = 2 mol NH3 The mole ratio must cancel out the units of mol NH3 given in the problem and leave the units of mol H2. Therefore, the mole ratio is N2 + 3H2  2NH3

Using Mole Ratios, continued Calculating Quantities in Reactions Using Mole Ratios, continued Sample Problem A Solution, continued

Understanding Concepts Exit Slip Understanding Concepts What is the mole ratio of CO2 to C6H12O6 in the combustion reaction: C6H12O6 + 6O2 6CO2 + 6H2O? A. 1:1 B. 1:2 C. 1:6 D. 6:1