lecture10 - Chem 1A Organic Chemistry C o v a le n t b o n...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Organic Chemistry Chem 1A
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Covalent bonds
Background image of page 2
Bond Stability How stable is a particular bond? Under conditions of constant pressure, the enthalpy chance Δ Hº is equal to the heat required for breaking a chemical bond in 1 mole of gaseous molecules. When Δ Hº is positive, heat is required, the process is endothermic . When Δ Hº is negative, heat is released, the process is exothermic . Because a chemical bond is a stable configuration, breaking it is an endothermic process The bond enthalpy is a measure of a bond’s stability
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Bond Enthalpies of diatomics H 2 (g) H(g) + H(g) Δ Hº = 436 kJ/mol Cl 2 (g) Cl(g) + Cl(g) Note that all atoms and molecules are in the gas state Δ Hº = 243 kJ/mol Chlorine molecule is less stable than hydrogen molecule HCl(g) H(g) + Cl(g) Δ Hº = 412 kJ/mol Breaking a single chemical bond: Breaking a multiple bond: N 2 (g) N(g) + N(g) Δ Hº = 941 kJ/mol
Background image of page 4
Bond Enthalpies of polyatomics Consider the methane molecule CH 4 . CH 4 (g) CH 3 (g) + H(g) Δ Hº = 435 kJ/mol CH 3 (g) CH 2 (g) + H(g) Δ Hº = 453 kJ/mol CH 2 (g) CH(g) + H(g) Δ Hº = 425 kJ/mol CH(g) C(g) + H(g) Δ Hº = 339 kJ/mol The average bond enthalpy of the C-H bond in methane is 1652/4 = 413 kJ/mol Not every consecutive C-H bond breaking is the same! Total = 1652 kJ/mol
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Bond Enthalpies
Background image of page 6
Thermochemistry of reactions We can use the bond enthalpies to predict the thermo- chemistry of a given reaction: H 2 (g) + 1/2 O 2 (g) H 2 O(g)
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 32

lecture10 - Chem 1A Organic Chemistry C o v a le n t b o n...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online