Chemistry Final

Chapter 13-19

Δ S (+)

Spontaneous

Δ S (-)

Nonspontaneous

Δ G (+)

Nonspontaneous

Δ G (-)

Spontaneous

Δ G^o = 0

Equilibrium

E_cell (+)

Spontaneous

E_cell (-)

Nonspontaneous

Polar vitamin

water soluble, not easily stored in body, excreted in urine

solution formation main factors

1) IMFs solute-solvent similar to pure solute and pure solvent 2) increased entropy upon mixing

Δ H_solute

Endothermic, breaking solute IMFs, H > 0

Δ H_solvent

Endothermic, breaking solvent IMFs, H > 0

Δ H_mix

Exothermic, formation of solute-solvent interactions, H < 0

H_solution = 0

solution will form if entropy increases

H_solution < 0

exothermic, solution forms if entropy increases, warm to touch

H_solution > 0

endothermic, solution forms if entropy increases, cool to touch

H_solute for ionic solute

negative H_lattice

H_solution = H_solute + H_hydration

Aqueous solutions with ionic solutes, where H_hydration = H_solvent + H_mix

saturated solution

no addition solute can dissolve, dissolved solute in dynamic equilibrium with solute solute

unsaturated solution

more solute can dissolve, no undissolved solute so no dynamic equilibrium

supersaturated solution

more than equilibrium amount of solute dissolved, unstable and precipitates easily

impact of temperature on solid solute

no effect

impact of temperature on gaseous solute

less soluble under higher temperatures

S_gas = K_HP_gas

Henry’s Law— quantifies the solubility of a gas (S) in a liquid by its partial pressure (P) above the liquid, where K is a constant at a given temperature.

S_gas

molarity (M)

K_H

Henry’s constant (M/atm)

P_gas

partial pressure of a gas solute above solution (atm)

Molarity (M)

mol / L

Molality (m)

mol / kg solvent

mole fraction

moles of a component divided by total moles in a mixture

percent by mass

mass of component / total mass of mixture * 100

ppm

mass solute/mass solution * 10⁶

ppb

mass solute/mass solution * 10⁹

colligative properties

properties that only depend on # of particles in solution

vapor pressure of a liquid

pressure of a gas above its liquid in equilibrium

vapor pressure lowering

solvent’s vapor pressure decreases when a solute is added

Raoult’s Law

P_solution = X_solvent P°_solvent

Ideal solution

A solution that follows Raoult's Law at all concentrations, exhibiting no significant interactions between solute and solvent.

Positive deviation from ideal solution

solute-solvent interactions are significantly weaker than solvent-solvent interactions

Negative deviation from ideal solution

solute-solvent interactions are significantly stronger than solvent-solvent interactions

van’t hoff factor (i)

ratio of moles of solute particles to moles of formula units dissolved. If a solute dissociates 100%, i is equal to the number of particles per formula unit.

ion pairing

oppositely charged ions associate in solution, causing i_measured to be lower than i_expected

collision model

reactions occur when particles collide, breaking and forming bonds. More collisions and higher energy collisions = faster rate

factors impacting reaction rates

concentration of reactants, temperature of reaction, structure and orientation of colliding particles

generalized reaction rate aA + bB —> cC + dD

(-1/a)(ΔA/Δt) = (1/c)(ΔC/Δt)

average rate

rate of a reaction over a time interval. can change as the reaction proceeds

instantaneous rate

rate of a reaction at a specific instant, equal to the slope of the tangent

rate law, A + B —> products

rate = k[A]^m[B]ⁿ

integrated rate laws

used for determining amount of reactant present at a certain time

linear relationship of zero order

[A]_t vs t

linear relationship of first order

ln[A]_t vs t

linear relationship of second order

1/[A]_t vs t

Frequency factor (A)

the number of times a reactant approaches the activation barrier. product of collision frequency (z) and orientation factor (p)

exponential factor

e^(-E_a/RT) the fraction of approaches with enough energy to surmount the activation barrier

elementary reaction

a single reaction that cannot be broken down into simpler steps. form a reaction mechanism

molecularity

number of reactant molecules involved in an elementary reaction. the lower the # of particles, the less stringent the requirements for effective collisions

rate law of elementary reaction

CAN be determined directly from stoichiometry

rate determining step

the slowest elementary reaction within a reaction mechanism. has the largest E_a

dynamic equilibrium

rate of forward rxn equals rate of reverse rxn

equilibrium constant

equilibrium ratio of concentrations/pressures of products raised to stoichiometric coefficients over the concentrations/pressures of reactants raised to their stoichiometric coefficients.

equilibrium constant dependence on balanced reaction

1. changing direction inverts K

2. multiplying coefficients by a factor raises K to that factor

3. when adding constituent reactions, K₁K₂=K_overall

reaction quotient (Q)

Q = K equilibrium

Q < K reaction will go forwards

Q > K reverse reaction will occur

Le Chatliers Principle

system will shift in direction to re establish equilibrium

Arrhenius acid

molecular compound that dissociates in water to form H⁺/H₃O⁺

Arrhenius base

compound that generates OH^- in water

six strong acids

HCl, HBr, HI, HNO₃, HClO₄, H₂SO₄

Bronsted-Lowery acid

proton (H⁺) donor

Bronsted-Lowery base

proton (H⁺) acceptor

neutralization reaction

H⁺ is transferred from an acid to a base

amphoteric

species can act as a base or acid (i.e., H₂O)

conjugate acid-base pairs

two substances related to each other by the transfer of a proton

Binary acid (HX) strength

increases down a group, increases across a period

Oxyacid (H-O-Y) strength

increases with the number of oxygen atoms and electronegativity of Y

impact of resonance stabilization on oxyacid strength

anions that exhibit resonance stabilization act as stronger acids when protonated

Acid ionization constant (K_A)

how much a weak acid dissociates in water. K_A=[H⁺][A^-]/[HA]

Autoionization of water

2H₂O (l) ⇌ H₃O⁺ (aq) + OH^- (aq)

Water dissociation constant (K_W)

K_W = [H₃O⁺][OH^-] = 1.0×10^-14 M

pH

-log[H₃O⁺]

pOH

-log[OH^-]

percent ionization of an acid (HA)

the percentage of added acid molecules that actually dissociate into H₃O⁺ and anion (A^-)

percent ionization

[H₃O⁺]/[HA] x 100%

pH of a single strong acid in water

calculate [H₃O⁺] from complete dissociation of strong acid, neglect [H₃O⁺] from auto ionization of water unless strong acid is very dilute

pH of two strong acids in water

calculate moles of H₃O⁺ separately and add, divide by total volume of solution (L) to get [H₃O⁺]

pH of single weak acid in water

calculate [H₃O⁺] from HA partial dissociation using an ICE table, typically neglect [H₃O⁺] from auto ionization of water.

pH of two weak acids in water

the weak acid with the larger K_A will dictate the pH of the overall mixture

pH of strong/weak acid mixture

calculate [H₃O⁺] from complete dissociation of strong acid, use as initial concentration in ICE table. use ICE table to calculate [H₃O⁺] from partial dissociation of weak acid to determine if contributes significantly to total [H₃O⁺]

Base Ionization Constant (K_B)

[BH⁺][OH^-]/[B]

pH of strong/weak base mixture

calculate [OH^-] from dissociation of strong base and use as initial [OH^-] in ICE table. use ICE table to calculate [OH^-] from weak base to see if contributes significantly to total

acid-base properties of ions

determined by the strength of its conjugate

Ions that do NOT impact pH

1. anions that are conjugate bases of STRONG acids

2. cations that are counter ions of STRONG bases

Ions that make solutions BASIC

1. anions that are conjugate bases of weak acids

Ions that make solutions ACIDIC

1. cations that are conjugate acids of weak bases

2. cations that are small and highly charged, forming a complex ion with water making an ionizable H⁺

Polyprotic acid

multiple ionizable protons, each dissociation step has its own K_A value

pH of a polyprotic acid

typically calculated using K_A of the first dissociation step, except in dilute solutions

H₂SO₄

special case where first dissociation step is complete but second is partial

Lewis acid

lone pair acceptor

Lewis base

lone pair donor

buffer

solution that resists pH changes. essential components: either a weak base and its conjugate acid or a weak acid and its conjugate base

common ion effect

when a weak acid is added to a solution that contains its anion, it will dissociate less due to Le Chatlier’s principle

calculating the pH of a buffer after adding strong component

1. allow strong component to react to completion

2. use Henderson hasselbalch and pK_a to calculate final pH

characteristics of an effective buffer

1. relative concentrations of weak components should be equal or close

2. absolute concentrations of weak components should be high