Presentation on theme: "Stoichiometric Relationships In Chemical Reactions"— Presentation transcript:
1 Stoichiometric Relationships In Chemical Reactions Unit 8Stoichiometric Relationships In Chemical ReactionsMole RatiosStoichiometry applied to gasesFractional Components of Chemical SamplesChemical Reactions Give Off or Take In EnergyLimiting And Excess Reagent ProblemsWorks best when seen as a slide show. Click the ‘Slide Show’ button on the lower right.
2 Mole RatiosThe coefficients of a chemical equation represent a ratio of moles. They are used to balance the equation thereby reflecting the Law of Conservation of Matter.This law states that thetotal number of atoms during a chemical reaction does not change because matter cannot be created nor destroyed.atoms are rearranged.
3 2 moles of H2 react with 1 mole of O2 to get 2 moles of H2O. Mole RatiosFor the equation2 H O2 ———> 2 H2O2 moles of H2 react with 1 mole of O2 to get 2 moles of H2O.Furthermore, the Law of Conservation of Matter shows thathydrogen atomsyields oxygen atoms2water molecules[6 atoms]
5 Q The salt potassium chlorate undergoes decomposition when heat is applied to form the salt potassium chloride and the gas oxygen.Write the balanced equation.What is the ratio of moles: potassium chlorate to potassium chloride to oxygen?23KClO3 KCl O223
6 Information Given by the Chemical Equation The coefficients in the balanced chemical equation shows the molecules and mole ratio of the reactants and productsSince moles can be converted to masses, we can determine the mass ratio of the reactants and products as well
7 Stoichiometry Rules! Write a chemical equation. Balance the equation! Determine start and destination for dimensional analysis.Convert start details into moles.Multiply by the appropriate mole ratio.Convert to correct units for destination.
8 Information Given by the Chemical Equation 2 CO + O2 —> 2 CO22 moles CO + 1mole O2= 2 moles CO2Since 1 mole of CO = g,1 mole O2 = g, and1 mole CO2 = g2(28.01) g CO + 1(32.00) g O2= 2(44.01) g CO2
9 Example #1 Write the balanced equation Determine the Number of Moles of Carbon Monoxiderequired to react with 3.2 moles Oxygen,and determine the moles of Carbon Dioxide producedWrite the balanced equation2 CO + O2 —> 2 CO2Use the coefficients to find the mole relationship2 moles CO = 1 mol O2 = 2 moles CO2
10 Example #1 Use dimensional analysis Determine the Number of Moles of Carbon Monoxiderequired to react with 3.2 moles Oxygen,and determine the moles of Carbon Dioxide producedUse dimensional analysis
11 Example #2 Write the balanced equation 2 CO + O2 —> 2 CO2 Determine the Number of grams of Carbon Monoxiderequired to react with 48.0 g Oxygen,and determine the mass of Carbon Dioxide producedWrite the balanced equation2 CO + O2 —> 2 CO2Use the coefficients to find the mole relationship2 moles CO : 1 mol O2 : 2 moles CO2Determine the Molar Mass of each1 mol CO = g1 mol O2 = g1 mol CO2 = g
12 Example #2Determine the Number of grams of Carbon Monoxiderequired to react with 48.0 g Oxygen,and determine the mass of Carbon Dioxide producedUse the molar mass of the given quantity to convert it to molesUse the mole relationship to convert the moles of the given quantity to the moles of the desired quantity
13 Example #2Determine the Number of grams of Carbon Monoxiderequired to react with 48.0 g Oxygen,and determine the mass of Carbon Dioxide producedUse the molar mass of the desired quantity to convert the moles to mass
14 KClO3 KCl O223If mole of potassium chlorate decomposed, how many moles of oxygen form?If 2.04 grams of potassium chloride were produced, how many grams of potassium chlorate must have decomposed?1.17= mol O2= g KClO33.35
16 One packaged meal for the USM service day: Determine the number of packaged meals based on the given supply:8 meals2 Excess oranges3 Excess sandwichescwx.prenhall.com
17 In the chemical reaction Mg(s) HCl(aq) ———> MgCl2(aq) H2(g)performed in many high school laboratories, more HCl is usually used than is needed. This is done to assure that all the magnesium reacts. The HCl, therefore, is in excess and some of it is left over when the reaction stops. No magnesium will be present once the reaction is over.
18 For another chemical reaction C + O2 CO2Initial supply of reactantProduct
19 1. In many chemistry problems you are told which reactant is in excess and solve based on the specified quantities of the other reactant.2. In some instances, however, you will be given quantities of both reactants. One is probably in excess, but you won’t be told which one.3. The following problem shows one way to determine the reactant that is in excess
20 Q. 5. 00 g of calcium reacts with 5 Q 5.00 g of calcium reacts with 5.00 g of sulfur in a composition reaction. Do a calculation to find thea) Excess reactant.Ca(s) + S(s) CaS(s)Higher.This means that S is in excess.In other words, after the reaction there will be CaS,unreacted S, and no Ca.
21 Q. 5. 00 g of calcium reacts with 5 Q 5.00 g of calcium reacts with 5.00 g of sulfur in a composition reaction. Do a calculation to find theb) Grams of product formed.Ca(s) + S(s) CaS(s)Start with the limiting reagent since all of it will be used up.Look what happens if you start with the excess reactant:
22 10.0 g of original reaction mixture – c) Calculate the grams of excess reactant unreacted once the reaction is completed.10.0 g of original reaction mixture –9.025 g of CaS formed= 1.0 g S left over
23 Determine which reactant is in excess. (ans. P) More Practice4.00 g of calcium is mixed with 4.00 g of phosphorus and ignited to get solid calcium phosphide, Ca3P2.Determine which reactant is in excess. (ans. P)How many grams of product were formed? (ans g)How many grams of the excess reactant were left over once the reaction was completed?(8 grams reactants – 6.05 grams calcium phosphide = 1.95 grams phosphorus left)