Exam 3 CH 101

Thermodynamics

Are reactants or products energetically favored?

study of energy and its transformations- interested in starting and ending points in E

Kinetics

How fast will the reaction happen and by what mechanism?

study of the process by which reactants form products • Interested in rates and mechanism (how fast and by which route)

1st Law of Thermodynamics

Energy is neither created nor destroyed…but energy can be converted from one form to another

∆E universe = 0

∆E universe = ∆E surroundings + ∆E system

Endothermic

delta H > 0, heat energy absorbed by system causing surroundings to cool, enthalpically UNfavorable (ex: ice pack)

(within thermo and enthalpy H)

Exothermic

delta H < 0, heat energy exits system causing surroundings to warm, enthalpically FAVorable(ex: hot hands)

(within thermo and enthalpy H)

Enthalpy

heat content of reaction, (endo or exothermic)

Entropy

amount of disorder, related to the # of ways energy can be distributed in a system

Bond Dissociation Energy

the energy input required to break 1 mole of a bond in the gas phase

Weak bonds

more reactive; require less energy to break

Strong bonds

more stable; require more energy to break

∆ H formula relating to bonds

∆H = sum of Bond Dissociation Energy of bonds broken - sum of Bond Dissociation Energy bonds formed

Gibbs Free Energy Equation

∆G = ∆H -T∆S

T= Temperature (K)

Spontaneous

∆G<0, products lower in energy than reactants, reaction proceeds

Non-spontaneous

∆G>0, products higher in energy than reactants, reaction does NOT (non) proceed

Entropically Favorable

∆S>0 (POSITIVE) increase in disorder, nature likes disorder

Entropically Unfavorable

∆S<0 (NEGATIVE) decrease in disorder, nature likes disorder

Larger Ea means what for the speed of the reaction

Slower

Smaller Ea means what for the speed of the reaction

Faster

3 ways to speed up a reaction

1. Increase temperature

2. Increase concentration of reactants

3. Use a catalyst

Equilibrium

Point at which the forward rate = reverse rate and concentrations of reactants and products remains constant

Equilibrium expression (Keq)

[D]^d [E]^e / [A]^a [B]^b

PRODUCTS / REACTANTS

Keq ~ 1

significant amount of both reactants and products present at equilibirum

Keq > > 1

extensive reaction, reaction goes “completely” to products

Keq < < 1

solution contains mainly reactants

Catalyst

molecular matchmaker, decreases energy of activation

Conjugate base

acid loses a proton and it is what remains after donated proton

Conjugate acid

base accepts a proton turning it into an acid

Lewis acid

Electron pair acceptor

Lewis base

Electron pair donor

Bronsted acid

H+/ proton donor (partial positive H atom)

Bronsted base

H+/ proton acceptor (lone pair on - or partial - atom which can be used to form a new covalent bond)

How to assess relative acidity

1. Atom holding - in conjugate base

• If comparing atoms in same row, compare EN

• If comparing atoms in same column, consider atomic radius

2. Consider resonance in conjugate base (more resonance structures —> more stable)