1 / 10

AP Chemistry Unit 7 – Thermodynamics

AP Chemistry Unit 7 – Thermodynamics. Lesson 6 – Bond Enthalpy Book Sections: 8.8. Covalent Bond Strength. The strength of a bond can be measured by determining how much energy is required to break the bond. This is the bond enthalpy .

kennan
Télécharger la présentation

AP Chemistry Unit 7 – Thermodynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. AP ChemistryUnit 7 – Thermodynamics Lesson 6 – Bond Enthalpy Book Sections: 8.8

  2. Covalent Bond Strength • The strength of a bond can be measured by determining how much energy is required to break the bond. • This is the bond enthalpy. • The bond enthalpy for a Cl-Cl bond, D(Cl-Cl), is measured to be 242 kJ/mol.

  3. Average Bond Enthalpies • This table lists the average bond enthalpies for many different types of bonds. (In Chapter 8) • Average bond enthalpies are positive, because bond breaking is an endothermic process.

  4. Enthalpies of Reaction • Yet another way to estimate H for a reaction is to compare the bond enthalpies of bonds broken to the bond enthalpies of the new bonds formed. • In other words, • Hrxn = (bond enthalpies of bonds broken) - • (bond enthalpies of bonds formed)

  5. Enthalpies of Reaction CH4(g) + Cl2(g) CH3Cl (g) + HCl (g) In this example, one C-H bond and one Cl-Cl bond are broken; one C-Cl and one H-Cl bond are formed.

  6. Enthalpies of Reaction So, H = [(C-H) + (Cl-Cl)] - [(C-Cl) + (H-Cl)] = [(413 kJ) + (242 kJ)] - [(328 kJ) + (431 kJ)] = (655 kJ) - (759 kJ) = -104 kJ

  7. Sample Problem Estimate H for the following reaction: C2H6 + 7/2 O2 2 CO2 + 3 H2O C-H : 413 kJ/mol C=O: 799 kJ/mol C-C : 348 kJ/mol O-H: 463 kJ/mol O=O: 495 kJ/mol

  8. Sample Problem Estimate H for the following reaction: C2H6 + 7/2 O2 2 CO2 + 3 H2O C-H : 413 kJ/mol C=O: 799 kJ/mol C-C : 348 kJ/mol O-H: 463 kJ/mol O=O: 495 kJ/mol -1416 kJ/mol

  9. Bond Enthalpy and Bond Length • We can also measure an average bond length for different bond types. • As the number of bonds between two atoms increases, the bond length decreases.

  10. HW: 8.66, 8.70, 8.72 (Read 19.1-19.3) • This week: • Tuesday: Entropy (19.1-19.3) • Wed-Fri: Midterm Exams • Ionic Equations Due Jan. 11 • Midterm Exam (Units 1-6): Jan. 14

More Related