CH 101 exam 3

∆E _universe= ∆E _system +∆E _surrounding

= 0

∆E _universe=

- ∆E _surrounding

∆E _universe= ___(q) + ___(w)

heat and work

enthalpy (H)

the heat of reaction (q) when work= 0 (when pressure is constant)

endothermic

heat energy absorbed by system (causing the surrounding to cool)

• ∆H>0

• UNFAVORABLE

• POSITIVE

exothermic

heat energy released by system (causing the surroundings to warm)

• ∆H<0

• FAVORABLE

• NEGATIVE

species in HIGHER energy

more reactive/less stable

species in LOWER energy

less reactive/more stable

weak bonds

more reactive, less stable

strong bonds

more stable, require more energy to break

bond energy/bond dissociation energy (D or BDE)

∆H= BDE of bonds broken - BDE of bonds formed

entropy (S)

amount of disorder present and number of ways energy can be distributed in a system

low entropy

• ordered system

• energy is concentrated

• -∆S<0 (high to low) (GAS to SOLID)

• UNFAVORABLE

high entropy

• disordered system

• energy can be spread out

• ∆S>0 (low to high) (SOLID to GAS)

• FAVORABLE

Gibbs free energy (G)

∆G= ∆H-T∆S

(T= temperature is in kelvin)

∆G<0 (negative); A —→ B is ______

spontaneous (reaction PROCEEDS)

• product is preferred

∆G>0 (positive); A——→B is

non-spontaneous (reaction does NOT proceeds)

• reactants preferred

How can we speed up a reaction?

1. increase temp.

   • more frequent collisions

   • gives collisions more energy to overcome E_a

2. increase concentration of reactants

• more frequent collisions

3. use a catalyst

   • brings reactant molecules together to facilitate their collisions

   • lowers the E_a (energy of activation)

equilibrium

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

• K_eq= [products]/[reactants]

there is a significant amount of both reactants and products present at equilibrium

K_eq=1

a very large K_eq means “extensive” reaction of the reaction goes “completely” to products

• >> greater than 1.0×10³

• extensive

• G<0

K_eq>1

a very small K_eq means that products are not favored. the solution contains mainly reactants

• <<1 less than 1.0×10^-3

• NOT extensive

• G>0

K_eq<1

le chatelelier’s principle

a system at equilibrium will respond to a stress in such a way to minimize the effect of the stress

stresses/ disturbances

1. changing product or reactants

2. changing temperature

bronsted acid:

• H⁺/ proton donated

• gives away/loses/supplies a proton

bronsted base

• H⁺/proton acceptor

• accepts/ takes on a proton

lewis acid

• electron pair acceptor

• accepts/ takes on a proton

lewis base

• electron pair donor

• gives away/loses/supplies a proton

attributes of bronsted acid (proton donor)?

S+ H atom

attributes of a bronsted base (proton acceptor)?

lobe pair on - or S- atom which can be used to form a new convalent bond

K_a- acid dissociation constant

the equilibrium constant (K_eq) for an acid reacting w/ water

the STRONGER acid, the LARGER the [conjugated base][H₃O], the ________

LARGER the K_a

• >> greater than 1.0×10³

• conjugate base is most stable base, least reactive base/ WEAKEST base

the WEAKER acid, the SMALLER the [conjugated base][H₃O], the ____

SMALLER the K_a

• << less than 1.0×10^-3

• conjugate base is least stable base, most reactive base/ STRONGEST base

pK_a, the STRONGER the acid, the ______

SMALLER (more NEGATIVE) the pK_a

• pK_a= -log(K_a)

pK_a the WEAKER the acid, the ______

LARGER (more POSITIVE) the pK_a

• pK_a= -log(K_a)

the stronger the parent acid, the ______

more STABLE the conjugate base

how to qualitatively assess relative acidity

1. atom holding - in conjugated base

   • comparing atoms in the same row, consider electronegativity

   • comparing atoms in the same column, consider size

2. consider resonance in conjugate base

3. consider e-donating and e-withdrawing groups in conjugate base

the reaction is extensive, if the reacting acid is much ______

STRONGER than the produced conjugate acid