Chem Exam 3

Entropy is favorable when…

ΔS > 0 (messy bedroom happens naturally, nature prefers high disorder)

Gibbs free energy is spontaneous when

ΔG < 0 (Products are lower in energy than reactants, reaction proceeds)

Transition state

Fleeting state between reactants and products where activation energy is the highest

What states of matter are omitted from equilibrium expressions?

Solids and Liquids

Keq >>> 1 means…

reaction is extensive/it goes completely to products (Keq > 1.0×10³)

Keq<<<1

Products are not favored, solution mostly has reactants (Keq < 1.0×10³)

• ΔG > 0

• Ea forward > Ea reverse

• Keq << 1

• Not extensive (reactants preferred)

• ΔG = 0

• Ea forward = Ea reverse

• Keq ~ 1

• Not extensive

• ΔG < 0

• Ea forward < Ea reverse

• Keq >> 1

• Extensive (products preferred)

Le Chatelier’s Principle

if a system at equilibrium is disturbed by changing conditions, the system will respond by bringing itself back to equilibrium

Endothermic equilibrium reactions

• Heat is a reactant

• When heated, converts reactants into products (shift L→R)

• When cooled, converts products into reactants (shift R→L)

Exothermic Equilibrium Reactions

• Heat is a product

• When heated, converts products into reactants (shift R→L)

• When cooled, converts reactants into products (shift L→R)

A higher energy species is

• More reactive

• Less stable

• Strong acid/base

A lower energy species is…

• Less reactive

• More stable

• Weak acid/base

pKa (inverse of Ka)

the stronger the acid the smaller the pKa

the weaker the acid the larger the pKa

The more electronegative the central atom…

the more stable the conjugate base is and the more acidic the acid it came from is (pKa gets smaller the more EN^-)

As atom size (going down the column) increases, pKa…

decreases (acid gets stronger), this is because larger atoms hold their electrons loosely making it easy to lose H^+

Also more stable

When should we look at resonance structures and what should we look for?

When the negative charge is on the same central atom, use resonance structures

If there is a negative charge adjacent to pi bonds, there are multiple resonance structures

What do more resonance structures mean

The more stable the conjugate base is and the more EN^- the central atom

Keq and Stability

Negative Keq means the reactants are favored, this makes them weaker and more stable (THE WEAKER THE ACID THE MORE STABLE)

Extensive reaction means

The reacting acid is stronger than the resulting conjugate base (small to big pKa)

For ΔG, if entropy and enthalpy are in agreement… (ex: both unfavorable)

Temperature doesn’t affect whether it is spontaneous or not