Quantity Relationships in Chemical Reactions Chapter 10 – Part 2 Quantity Relationships in Chemical Reactions Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Section 10.4 Limiting Reactants: The Problem Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

How many carbon dioxide molecules will result? Three atoms of carbon and two molecules of oxygen react until one is used up. How many carbon dioxide molecules will result? The reaction will stop when two molecules of oxygen are used up. Two carbon dioxide molecules form. Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

The reactant that is completely used up by the reaction (oxygen) Limiting reactant: The reactant that is completely used up by the reaction (oxygen) Excess reactant: The reactant initially present in excess, relative to the limiting reactant (carbon) Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Section 10.5 Limiting Reactants: Comparison-of-Moles Method Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Goal 4 Given a chemical equation, or information from which it may be determined, and initial quantities of two or more reactants, (a) identify the limiting reactant, (b) calculate the theoretical yield of a specified product, assuming complete use of the limiting reactant, and (c) calculate the quantity of reactant initially in excess that remains unreacted. Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Comparison-of-Moles Method How to Solve a Limiting Reactant Problem 1. Convert the number of grams of each reactant to moles 2. Identify the limiting reactant. 3. Calculate the number of moles of each species that reacts or is produced. 4. Calculate the number of moles of each species that remains after the reaction. 5. Change the number of moles of each species to grams. Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. Example: A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. How many grams of hydrogen will be produced? How many grams of which reactant will be left over? + H2O 2 H2 2 Na + NaOH 2 Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

+ 2 H2O H2 2 Na + 2 NaOH Grams at start 24.0 Molar mass, g/mol 22.99 Molar mass, g/mol 22.99 18.02 2.016 40.00 Moles at start 1.04 1.33 Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

+ 2 H2O H2 2 Na + 2 NaOH Moles at start 1.04 1.33 Moles used, produced Moles used, produced – 1.04 + 1.04 + 0.52 Moles at end 0.29 0.52 1.04 Grams at end 5.2 1.0 41.6 Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. + 2 H2O H2 2 Na + 2 NaOH Grams at end 5.2 1.0 41.6 A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. How many grams of hydrogen will be produced? How many grams of which reactant will be left over? 1.0 gram of hydrogen is produced; 5.2 grams of water is left over Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Section 10.6 Limiting Reactants: Smaller-Amount Method Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Goal 4 Given a chemical equation, or information from which it may be determined, and initial quantities of two or more reactants, (a) identify the limiting reactant, (b) calculate the theoretical yield of a specified product, assuming complete use of the limiting reactant, and (c) calculate the quantity of reactant initially in excess that remains unreacted. Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Smaller-Amount Method How to Solve a Limiting Reactant Problem 1. Calculate the amount of product that can be formed by the initial amount of each reactant. a) The reactant that yields the smaller amount of product is the limiting reactant. b) The smaller amount of product is the amount that will be formed when all of the limiting reactant is used up. 2. Calculate the amount of excess reactant that is used by the total amount of limiting reactant. 3. Subtract from the amount of excess reactant present initially the amount that is used by all of the limiting reactant. The difference is the amount of excess reactant that is left. Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. Example: A 24.0-g piece of solid sodium is added to 24.0 g of liquid water. How many grams of hydrogen will be produced? How many grams of which reactant will be left over? + H2O 2 H2 2 Na + NaOH 2 Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

GIVEN: 24.0 g Na WANTED: g H2 H2 2 Na + HOH 2 + NaOH 2 X 1 mol Na 1 mol H2 2 mol Na X 2.016 g H2 mol H2 = 1.05 g H2 Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

GIVEN: 24.0 g H2O WANTED: g H2 Na + HOH H2 + NaOH 2 X 1 mol H2O Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

Therefore 1.05 g H2 is produced and Na is the limiting reactant 24.0 g Na and unlimited H2O produces 1.05 g H2 24.0 g H2O and unlimited Na produces 1.34 g H2 Therefore 1.05 g H2 is produced and Na is the limiting reactant Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

How much of the excess reactant, H2O, is consumed by the reaction of 24.0 g Na? GIVEN: 24.0 g Na WANTED: g H2O Na + HOH H2 + NaOH 2 X 2 mol H2O 2 mol Na X 1 mol Na 22.99 g Na 24.0 g Na X 18.02 g H2O mol H2O = 18.8 g H2O Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.

How much of the excess reactant, H2O, remains when the reaction is complete? 24.0 g H2O initially – 18.8 g H2O reacted 5.2 g H2O remains Presentation Slides to Accompany Cracolice/Peters Introductory Chemistry: An Active Learning Approach, Third Edition Copyright © 2007 Brooks/Cole, a part of the Thomson Corporation.