unit 3 - acid and base

Question 1

define: homolytic and heterolytic bond cleavage; homogenic and heterogenic bond formation

Answer 1

• rxn gives 2 free radicals
• one atom gets both electrons and the other gets none; referred as polar reactions
• combination of free radicals
• opposite of heteolytic bond cleavage

Question 2

Define Bronsted Lowry Acid and Base

define: protonation and deprotonation, explain pKa and Ka

Answer 2

• talking about protons: H+
• BL Acid is a proton donor
• BL base is a proton acceptor
• deprotonation: when an acid gives up its proton/base removing a proton from an acid
• protonation: base receices a proton from an acid
• strong acids have a low pKA and weak acids have a high pKA
• Ka= measure of how readily a acid gives up a proton
• equilibrium always favours the side with the weaker acid and weaker base

Question 3

How to predict acid strength?

5 things

Answer 3

• strength of an acid depneds on the stability of the conjugated base (the species left after deprotonation)

1. EN: if the negative charge is on an EN, it can be easily stablized
2. Polarization: the ability of an atom to alter its electron distribution in response to an external influence; larger the atom the more polarizable = more better able to stabilize a charge
3. Declocalization: Resonacne stabilization; ability to have resonance can stabilize the charge better
4. inductive effects: EN substituents on acids decrease pKa(stronger acid) by helping to stabilized the deprotonated species
5. Atom hybridization: the more s-character= more acidity; s-orbitals are closer to the nucles, thus the charge is more stabilize with the protons; sp,sp2,sp3

Question 4

Define Lewis acids and base

Answer 4

• talks about the electrons
• L Acid = electron acceptor
• L base = electron donor; non-bonding electrons that can be donated

Question 5

draw out an reaction graph

label: E, rxn coordinate, Ea, Transition state, G free enegy

Answer 5

• transition state: when two molecules collide during a rxn they pass through a transition state; hgiher energy “species” between the starting material and the products
• Gibss Free Energy must be negative for the rxn to proceed

Question 6

define enthalpy and entropy

Answer 6

1. heat; H>0 endothermic; H<0 exothermic
2. chaos; S<0 decrease in order; S>0 increase in order

Question 7

what is a reaction intermediate and define the RDS

Answer 7

1. species form briefly during the course of a rxn; has a finite lifetime and often can be detected and characterized
2. slowest step in a rxna n the step with the highest energy transition state

Question 9

What are the factors that dtermine the rate of a rxn?

Answer 9

1. temperature
2. concentration
3. catalysis