Chapter 2 Lecture 1 Kinetics/Thermo & Acids/Bases

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Chapter 2 Lecture 1 Kinetics/Thermo & Acids/Bases. Review of Simple Kinetics and Thermodynamics Definitions Thermodynamics = changes in energy during a process or reaction. Determines extent of completion of the reaction or process

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## Chapter 2 Lecture 1 Kinetics/Thermo & Acids/Bases

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Chapter 2 Lecture 1 Kinetics/Thermo & Acids/Bases
• Review of Simple Kinetics and Thermodynamics
• Definitions
• Thermodynamics = changes in energy during a process or reaction. Determines extent of completion of the reaction or process
• Kinetics = rate of a process or reaction. Determines how fast the reaction or process occurs.
• Equilibria
• Equilibrium = state of a system in which the concentrations of reactants and products are no longer changing.
• Equilibrium Constant
• If K is large, reaction goes forward
• If K is small, reaction goes in reverse
• DG0 = Gibb’s Free Energy Change = describes the overall energy change as a reaction reaches equilibrium
• DG0 = -RTlnK

R = 1.986 cal/deg mol

T = temperature in Kelvins (oC + 273)

• When K = 10, DG0 = -1.36 kcal/mol (at T = 298K)
• When K = 0.1, DG0 = +1.36 kcal/mol
• When K = 1, DG0 = 0
• Relating DG0 to Enthalpy and Entropy
• DG0 = DH0 - TDS0
• DH0 = Enthalpy = Broken Bond Strengths – Formed Bond Strengths
• -DH0 = Exothermic reaction (gives off energy)
• + DH0 = Endothermic reaction (requires energy input)
• DS0 = Entropy = Amount of order in the system
• - DS0 = less disorder (fewer molecules in the system)
• + DS0 = more disorder (more molecules in the system)
Reaction Rates
• Activation Energy determines reaction rates
• Small Ea = fast reaction
• Large Ea = slow reaction
• Rate Constants
The Arrhenius Equation

A = maximum rate constant possible = different for each reaction

High T -Ea/RT becomes small e0 = 1 k = A

• Review of Acids and Bases
• Bronsted Acids/Bases
• Acid = H+ donor
• Base = H+ acceptor
• Ionization of Water: H2O + H2O H3O+ + OH-
• pH = -log[H3O+]
• pKa = -logKa = pH at which HA is half-dissociated
• pKa + pKb = 14

If you know Ka, Kb, pKa, pKb, you can find all others

Ka

Predicting Acid/Base Strength
• Size of A-: HI > HBr > HCl > HF
• F- is small, more concentrated charge, holds on to H+
• I- is large, less concentrated charge, gives up H+
• Electronegativity of A-: HF > H2O > NH3 > CH4
• Resonance Forms of A-
• Lewis Acids and Bases
• Lewis Acid = electron pair acceptor
• Lewis Base = electron pair donor
• Some covalently bonded molecules can be considered Lewis Acid/Base pairs
• Dissociation of a Lewis Acid/Base Pair (Mechanisms)