University:
York University
Course:
CHEM 1000 | Chemical Structure
Academic year:

2021
Views:

271

Pages:

2
Author:

Niklas

Lecture 13 (02/25/21) Chemical Reactivity & Mechanisms Molecules have potential to undergo Δ/rxns Relationship b/w PE & Stability/Rxn Mechanical Analogy Less PE = less able to undergo Δ Higher PE = Higher Reactivity = Low Stability Lower PE = Lower Reactivity = High Stability Understanding Rxn Mechanisms "Elementary Rxn" Transition State: Species become "loose" [A-B] Free Energy (G) Free E of Reactants (G) Free E of Products ΔG = G(products) - G(reactants) ΔG < 0 = spontaneous process ΔG > 0 = non-spontaneous process Reaction Coordinate (progress) How does G change during the reaction? What are the intermediates? (+) endothermic (-) exothermic ΔG° = ΔH° - TΔS° Rxns are driven by min. of ΔG, NOT ΔH ΔG = ΔH @ low temp. ΔH°/Enthalpy Heat E. xch b/w Rxn & its surroundings. Bond Breaking: endothermic Bond Forming: exothermic BDE (kcal/mol) X-H H-H: 104 H-Cl: 103 H-F: 136 H-I: 71 H-OH: 119 C-C CH₃-CH₃: 88 (CH₃)₂CH-CH₃: 84 CH₃-Br: 70 CH₃-I: 51 More branching = weaker C-C bond More atoms = weaker C-C BDE don't vary much S-O, Cl-O, N-N, X-X weak bonds C-H display important patterns Read Ch. 6.03! Gibbs Free E.