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 (in gas state only)

Keq ~ 1

significant amount of both reactants and products present at equilibirum

Keq > > 1

extensive reaction, reaction goes “completely” to products. spontaneous

Keq < < 1

solution contains mainly reactants

Catalyst

molecular matchmaker (brings reacting molecules physically closer together to allow for their collision to be in the correct orientation), decreases Ea, increases rate of reaction, NO AFFECT on delta G

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)

3. Consider electron donating and withdrawing groups

Effect of higher energy on reactivity stability and strength

higher reactivity, lower stability, higher strength

Effect of lower energy on reactivity stability and strength

lower reactivity, higher stability, and lower strength