Stoichiometry Chapter 9

Stoichiometry Def: study of mass relationships in chemical reactions Def: study of mass relationships in chemical reactions 1. Mole conversions 2. Relationship between products and reactants

Stoichiometry Revolve around balanced equations: Revolve around balanced equations: Coefficients = # particles Coefficients = # particles # of MOLES of particles # of MOLES of particles 2H 2 + O 2  2H 2 O 2 moles H mole O 2  2 moles H 2 O

Stoichiometry MOLAR RATIOS!! MOLAR RATIOS!! 2H 2 + O 2  2H 2 O 2H 2 + O 2  2H 2 O Molar ratio of: Molar ratio of: H 2 : O 2 ? H 2 : O 2 ? H 2 : H 2 O H 2 : H 2 O O 2 : H 2 O O 2 : H 2 O Use these as conversion factors! Use these as conversion factors!

Mole-Mole Problems 2H 2 + O 2  2H 2 O 2H 2 + O 2  2H 2 O How many moles of H 2 are required to react with 2.5 mole O 2 ? How many moles of H 2 are required to react with 2.5 mole O 2 ? How many moles of Al(NO 3 ) 3 are produced when.75 mol AgNO 3 reacts with Al? How many moles of Al(NO 3 ) 3 are produced when.75 mol AgNO 3 reacts with Al?

Mass-Mole Problems Fe 2 O 3 + Al  Al 2 O 3 + Fe Fe 2 O 3 + Al  Al 2 O 3 + Fe How many moles of Fe are produced when 5.50 g of Fe 2 O 3 reacts? How many moles of Fe are produced when 5.50 g of Fe 2 O 3 reacts? How many moles of water are required to react with.25 g of Na? How many moles of water are required to react with.25 g of Na?

Mole-Mass Problems Mg + O 2  MgO Mg + O 2  MgO How many grams of MgO can be produced from 2.95 mol Mg reacting with oxygen? How many grams of MgO can be produced from 2.95 mol Mg reacting with oxygen? F 2 + KBr  KF + Br 2 F 2 + KBr  KF + Br 2 What mass of KBr is needed to react with 0.96 mol F 2 ? What mass of KBr is needed to react with 0.96 mol F 2 ?

Mass-Mass Problems Sodium phosphate reacts with magnesium nitrate Sodium phosphate reacts with magnesium nitrate If you have 3.12g of magnesium nitrate, how many grams of magnesium phosphate will you produce? If you have 3.12g of magnesium nitrate, how many grams of magnesium phosphate will you produce?

Helpful Sites Mole - Mole Mole - Mole nsmolestomolescsn7.html nsmolestomolescsn7.html Mass - Mass Mass - Mass nsgramstogramscsn7.html nsgramstogramscsn7.html

Limiting Reactants

Amount of products depends on amount of reactants Amount of products depends on amount of reactants Car runs because gas reacts with O 2 Car runs because gas reacts with O 2 Out of gas = car doesn’t run Out of gas = car doesn’t run Gas = limiting reactant Gas = limiting reactant

Limiting Reactants Limiting reactant – reactant that limits the amount of product Limiting reactant – reactant that limits the amount of product Amount of product will ONLY be amount made from limiting reactant Amount of product will ONLY be amount made from limiting reactant Excess reactant – reactant that is not used up completely Excess reactant – reactant that is not used up completely

Finding the Limiting Reactant 1. Balance the equation 2. Pick 1 product and calculate the amount of product produced from both reactants 3. Reactant that produced the smallest amount of product is limiting reactant

More about Limiting Reactants Fe + S  FeS Fe + S  FeS 650. g Fe reacts with 650. g S, what is the LR? 650. g Fe reacts with 650. g S, what is the LR? What is the mass of sulfur in excess? What is the mass of sulfur in excess? ich.php ich.php ich.php ich.php

Finding the Limiting Reactant Cu + AgNO 3  Cu(NO 3 ) 2 + Ag Cu + AgNO 3  Cu(NO 3 ) 2 + Ag If 3.1 mol Cu and 3.1 mol AgNO 3 react, what is the limiting reactant? If 3.1 mol Cu and 3.1 mol AgNO 3 react, what is the limiting reactant? How many grams of Ag will be produced? How many grams of Ag will be produced? Mass excess reactant unreacted? Mass excess reactant unreacted?

Percent Yield Amount you calculate isn’t what you always produce Amount you calculate isn’t what you always produce Lab errors Lab errors Theoretical Yield – amount produced based on calculations Theoretical Yield – amount produced based on calculations

Percent Yield Actual Yield – amount of product “actually” obtained from lab Actual Yield – amount of product “actually” obtained from lab Percent Yield – percent of product you actually recovered in lab Percent Yield – percent of product you actually recovered in lab

Percent Yield % Yield = actual yield x 100 % Yield = actual yield x 100 theoretical yield theoretical yield

Percent Yield Pb(NO 3 ) 2 + KI  PbI 2 + KNO 3 Pb(NO 3 ) 2 + KI  PbI 2 + KNO 3 Determine the % yield if 16.4 g Pb(NO 3 ) 2 reacts with 28.5 g KI if 18.3g PbI 2 is produced. Determine the % yield if 16.4 g Pb(NO 3 ) 2 reacts with 28.5 g KI if 18.3g PbI 2 is produced.