Stoichiometric Calculations Slide 3 / 109 Slide 4 / 109 Table of - PDF document

Slide 1 / 109 Slide 2 / 109 Stoichiometric Calculations Slide 3 / 109 Slide 4 / 109 Table of Contents Stoichiometry Calculations Click on the topic to go to that section with Moles · Stoichiometry Calculations with Moles · Stoichiometry Calculations with Particles and Volume · Stoichiometry Calculations with Mass · Mixed Stoichiometry Problems · Limiting Reactants · Theoretical, Actual and Percent Yield · Calculating Excess Reactants Return to Table of Contents Slide 5 / 109 Slide 6 / 109 Stoichiometry Stoichiometry in our daily lives The word stoichiometry is derived from two Greek words. Airbags save thousands of lives every "stoicheion" meaning element and "metron", meaning measure. year. When a collision happens, the following reaction occurs. 2NaN 3 (s) --> 2Na(s) + 3N 2 (g) In order to properly inflate, roughly 50 L of nitrogen gas must be produced. NaN 3 capsule Engineers have determined, using stoichiometry, that about 96 grams of NaN 3 are needed to react in each airbag capsule to produce enough nitrogen gas.

Slide 7 / 109 Slide 8 / 109 Stoichiometric Calculations Stoichiometric Calculations A balanced chemical equation is needed to perform any stoichiometric calculations. The coefficients in the balanced equation give the ratio of moles of reactants and products. N 2 + 3H 2 ---> 2NH 3 2 H 2 + O 2 --# 2 H 2 O 1 mol N 2 3 mol H 2 1 mol N 2 can be read as: 3 mol H 2 2 mol NH 3 2 mol NH 3 2 moles of H 2 plus 1 mole of O 2 yields 2 moles of H 2 O The above ratios can be used to determine the quantity of any reactant and products. giving ratios of: For every 1 mol of N 2 , you would need 3 mol of H 2 to completely react with · 2 mol H 2 2 mol H 2 1 mol O 2 you would produce 2 mol of NH 3 1 mol O 2 2 mol H 2 O 2 mol H 2 O · Slide 9 / 109 Slide 10 / 109 Stoichiometry Calculations with Moles Stoichiometric Calculations with Moles 2 H 2 + O 2 2 H 2 O 1. Use the equation to set Using this interpretation it's straightforward to answer 2 mol H 2 O up a ratio of the substances questions about the relative number of moles of reactants of interest. 2 mol H 2 and products. 2. Set that equal to the ratio n mol H 2 O 2 mol H 2 O For instance, use the balanced equation below to determine = of the known to unknown 8 mol H 2 2 mol H 2 the maximum number of moles of H 2 O that could be created quantities of the same from reacting 8 moles of H 2 . substances. 2 H 2 + O 2 2 H 2 O 8(2) = (2) n mol H 2 O 3. Solve for the unknown. n = 8 mol H 2 O Slide 11 / 109 Slide 12 / 109 Stoichiometry Calculations with Moles Stoichiometry Calculations with Moles 2 H 2 + O 2 - -# 2 H 2 O Another Example: 1. Use the formula to set up 1 mol O 2 a ratio of the substances of 2 mol H 2 2 H 2 + O 2 2 H 2 O interest. Given the equation: 2. Set that equal to the ratio 1 mol O 2 n mol O 2 = of the known to unknown How many moles of oxygen would be needed to react with 12 mol H 2 2 mol H 2 quantities of the same 12 moles of H 2 ? substances. 12(1) = (2)n O 2 3. Solve for the unknown by cross multiplying. = 6 n O 2

Slide 13 / 109 Slide 14 / 109 Stoichiometry Calculations Real World Application 2 H 2 + O 2 -# 2 H 2 O 2Al + Fe 2 O 3 --> 2Fe + Al 2 O 3 + 859 kJ of energy Given 12 moles of H 2 , how much O 2 and H 2 O would be needed or The thermite reaction produced? (above) releases a lot of Using the ratios, you would need..... heat and is used in to weld railroad tracks together. 1/2 as much O 2 as H 2 (ratio is 1 mol O 2 /2 mol H 2 ) 12 mol H2 x 1 mol O 2 = 6 mol O 2 needed How many moles of Al would be needed to produce 7.8 moles of 2 mol H 2 Al 2 O 3 ? Using the ratios, you would produce..... An equal amount of H 2 O as H 2 used (ratio is 2 mol H 2 O/2 mol H 2 ) 12 mol H 2 x 2 mol H 2 O = 12 mol H 2 O move for 7.8 mol Al 2 O 3 x 2 mol Al = 15.6 mol Al 2 mol H 2 answer 1 mol Al 2 O 3 Slide 15 / 109 Slide 16 / 109 What is the largest number of moles of Al 2 O 3 1 2 How many moles of O 2 would be required to that could result from reacting 6 moles of O 2 ? create 12 moles of Al 2 O 3 ? 2 (g) - - # 2 Al 2 O 3 (s) 4 Al (s) + 3 O 2 (g) - - # 2 Al 2 O 3 (s) 4 Al (s) + 3 O Slide 17 / 109 Slide 18 / 109 How many moles of O 2 would be required to 4 When iron rusts in air, iron (III) oxide is produced. 3 How many moles of oxygen react with 2.4 mol of Fe completely react with 8 moles of Al? in this reaction? 2 (g) - - # 2 Al 2 O 3 (s) 4 Al (s) + 3 O 4 Fe (s) + 3 O 2 (g)--> 2 Fe 2 O 3 (s)

Slide 19 / 109 Slide 20 / 109 6 How many moles of calcium metal are produced 5 How many moles of aluminium are needed to react from the decomposition of 8 mol of calcium completely with 1.2 mol FeO? chloride? 2 Al (s) + 3 FeO (s) --> 3 Fe (s) + Al 2 O 3 (s) CaCl 2 (s) --> Ca (s) + Cl 2 (g) Slide 21 / 109 Slide 22 / 109 7 How many moles (total) of calcium metal and 8 How many moles of Ag are needed to react with 40 chlorine gas are produced from the moles of HNO 3 ? decomposition of 8 mol of calcium chloride? 3 Ag(s) + 4 HNO 3 (aq) --> 3 AgNO 3 (aq) + 2 H 2 O(l) + NO(g) CaCl 2 (s) --> Ca (s) + Cl 2 (g) Slide 23 / 109 Slide 24 / 109 9 How many moles of AgNO 3 could be produced from 10 How many moles of water would be produced when 40 moles of HNO 3 ? 0.4 moles of Ag react with an excess amount of HNO 3 ? 3Ag(s) + 4HNO 3 (aq) --> 3AgNO 3 (aq) + 2 H 2 O(l) + NO(g) 3Ag(s) + 4HNO 3 (aq) --> 3AgNO 3 (aq) + 2 H 2 O(l) + NO(g)

Slide 25 / 109 Slide 26 / 109 11 How many moles of NO were produced if 16 moles of 12 How many moles of N 2 H 4 are required to produce 57 water were made during the reaction? moles of nitrogen gas? 3Ag(s) + 4HNO 3 (aq) --> 3AgNO 3 (aq) + 2 H 2 O(l) + NO(g) 2 N 2 H 4 (l) + N 2 O 4 (l) ---> 3 N 2 (g) + 4 H 2 O(g) Slide 27 / 109 Slide 28 / 109 13 How many moles of dinitrogen tetraoxide would be 14 How many moles of water are produced if 57 moles needed to produce 57 moles of nitrogen gas? of nitrogen gas are produced? 2 N 2 H 4 (l) + N 2 O 4 (l) ---> 3 N 2 (g) + 4 H 2 O(g) 2 N 2 H 4 (l) + N 2 O 4 (l) ---> 3 N 2 (g) + 4 H 2 O(g) Slide 29 / 109 Slide 30 / 109 15 How many total moles of gas would be produced when 5 moles of nitrogen tetrahydride reacts with excess N 2 O 4 ? Stoichiometry Calculations 2 N 2 H 4 (l) + N 2 O 4 (l) ---> 3 N 2 (g) + 4 H 2 O(g) with Particles and Volume Return to Table of Contents

Slide 31 / 109 Slide 32 / 109 Stoichiometry Calculations with Particles 16 What is the largest number of of Li 3 N formula units that could result from reacting 6 N 2 molecules? The number of particles (atoms, molecules, formula units) is directly 6 Li (s) + N 2 (g) --# 2 Li 3 N (s) to proportional to the number of moles. Therefore... 2 H 2 + O 2 --> 2 H 2 O can be read as: 2 molecules of H 2 plus 1 molecule of O 2 yields 2 molecules of H 2 O. Note...while moles can be expressed as non-whole numbers, particles must be whole numbers. One cannot have 6.1 atoms, molecules, or formula units! Slide 33 / 109 Slide 34 / 109 17 How many N 2 molecules would be required 18 How many Li atoms would be required to to create 4 Li 3 N formula units? completely react with 3 N 2 molecules? 6 Li (s) + N 2 (g) --# 2 Li 3 N (s) 6 Li (s) + N 2 (g) --# 2 Li 3 N (s) Slide 35 / 109 Slide 36 / 109 Stoichiometry Calculations with Volumes 19The equation below shows the decomposition of lead nitrate. How many liters of oxygen are At a given temperature and pressure, the space a sample of a gas takes produced when 12L of NO 2 are formed? (STP) up (it's volume) is proportional to the number of moles of gas molecules present. Therefore... 2Pb(NO 3 ) 2 (s) --> 2PbO (s) +4NO 2 (g) + O 2 (g) 2 H 2 (g) + O 2 (g) --> 2 H 2 O(g) can be read as: 2 volumes of H 2 plus 1 volume of O 2 yields 2 volumes of H 2 O. Note: The volume of a material is only proportional to the number of moles when the substance is in the gas phase!

Slide 37 / 109 Slide 38 / 109 21 How many liters of H 2 O (g) will be created from 20 What volume of methane is needed to completely reacting 8.0 L of H 2 (g) with a sufficient amount react with 500 mL of O 2 at STP? (Balance the of O 2 (g)? equation first!!!) 2 H 2 (g) + O 2 (g) --# 2 H 2 O (g) __ CH 4 + ___ O 2 --# ___ CO 2 + ___ H 2 O Slide 39 / 109 Slide 40 / 109 22 How many liters of NO 2 (g) will be created from Stoichiometry with Particles and Volumes reacting 36 L of O 2 (g) with a sufficient amount of NH 3 (g)? It's common to be asked to report a value in a unit other than the one 4 NH 3 (g) + 7 O 2 (g) --# 4 NO 2 (g) + 6 H 2 O (g) given. For example: Given the following reaction, how many L of nitrogen gas would be needed to produce 3 moles of ammonia? N 2 (g) + 3H 2 (g) --> 2NH 3 Slide 41 / 109 Slide 42 / 109 Stoichiometry with Particles and Volumes Stoichiometry with Particles and Volumes Example 2: How many moles of Cl 2 gas would be needed to produce Given the following reaction, how many liters of nitrogen gas would be 3 x 10 24 formula units of NaCl given the following reaction. needed @STP to produce 3 moles of ammonia? 2Na(s) + Cl 2 (g) --> 2NaCl(s) N 2 (g) + 3H 2 (g) --> 2NH 3 formula units NaCl --> molecules Cl 2 --> mol Cl 2 mol NH 3 --> mol N 2 --> L N 2 3 x 10 24 formula units NaCl x 1 molecule Cl 2 x 1 mol Cl 2 2 for. units NaCl 6.02 x 10 23 molecules 3 mol NH 3 x 1 mol N 2 x 22.4 L = 33.6 L N 2 2 mol NH 3 1 mol = 2.5 mol Cl 2