Chapter 12 Stoichiometry

Like a Recipe A balanced chemical equation provides the same kind of quantitative information that a recipe does.

What is it?? Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or product is formed in a reaction. The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry

Let’s Look at an everyday example! In a five day work week, tiny tike is scheduled to make 640 tricycles. How many wheels should be in the plant on Monday morning to make those tricycles?

Interpreting Chemical Equations A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles; mass; and volume.

Interpreting (Cont.)

Interpreting (cont.) Always remember : Mass and atoms are always conserved in a chemical reaction.

Example of Interpreting a Chemical reaction

Section 2 Chemical Calculations

Writing and Using Mole Ratios Mole Ratios are used to convert between: moles of reactant and moles of product moles of reactants moles of products A mole ratio is a conversion factor derived from the coefficients of a balanced chemical equation interpreted in terms of moles.

Example #1 List the mole ratios present in the equation

Example #2

Practice on your own Page 360 #11

Mass to Mass claculations

Example #4

Practice on your Own Page 361 # 13

Other Stoichiometric Calculations In a typical stoichiometric problem, given quantity is first converted to moles mole ratio from the balanced equation is used to calculate the number of moles of the wanted substance moles are converted to any other unit of measurement related to the unit mole, as the problem requires

Problem Solving Approach

Practice on your own Page 364 # 15

Volume- Volume

12.3 Limiting reagent and Percent yield

Limiting Reagent and Excess Reagent limiting reagent is the reagent that determines the amount of product that can be formed by a reaction Excess Reagent- is the reagent not used up (what is left over in a chemical reaction)

Example Chemical Equation for the preparation of Ammonia

Example #1

Practice on your own Page 370 # 25

Example # 2

Percent Yield The percent yield is a measure of the efficiency of a reaction carried out in the laboratory. Theoretical yield -maximum amount of product that could be formed from given amounts of reactants Actual yield the amount of product that actually forms when the reaction is carried out in the laboratory

Example #1 (Percent Yield )

Example #2 percent yield

Practice on your own Page 374-375 # 29 and 31