CHM2046 Exam 2

system

the substances involved in the chemical and physical changes under investigation

surroundings

the environment around the system

universe

the system plus the surroundings

first law of thermodynamics

states that energy cannot be created or destroyed, only transformed from one form to another

total energy of the universe is ___, so the change in energy of the universe is ___

constant, zero

second law of thermodynamics

in any spontaneous change, the universe tends toward a state of increasing entropy; entropy of the universe (not the system) increases during a spontaneous process

ΔS (universe) > 0

spontaneous

ΔS (universe) < 0

nonspontaneous (spontaneous in the reverse reaction)

ΔS (universe) = 0

at equilibrium

spontaneous changes happen ___ any continuing outside influences

without

a spontaneous change has a natural direction

always towards equilibrium

product-favored

spontaneous

reactant-favored

nonspontaneous

thermodynamic spontaneity is ___ related to speed

not

two factors that affect the spontaneity of any physical or chemical change

1. spontaneity is favored when heat is released during the change (exothermic)

2. spontaneity is favored when the change causes an increase in the dispersal of energy and matter (entropy increases)

entropy (S)

a measure of randomness and disorder

how phase changes affect entropy changes

solid < liquid < gas

factors that increase entropy change

1. the S of any sample increases as its T increases (molecules have increased kinetic energy)

2. the S of a gas increases as its V increases

3. mixing of substances or dissolving a solid in a liquid causes an increase in S

standard conditions

1. P = 1 bar or 1 atm

2. T = 298K

3. 1 mole of substance

in an exothermic change, heat ___ by the system is absorbed by the surroundings

released

in an endothermic change, heat ___ by the system is released by the surroundings

absorbed

Gibb’s free energy (ΔG)

the maximum energy available to do useful work; the minimum work that must be done to a system to make a spontaneous process

ΔG > 0

nonspontaneous (spontaneous in reverse reaction)

ΔG < 0

spontaneous

ΔG = 0

at equilibrium

K > 1

products are more abundant

K < 1

reactants are more abundant

K = 1

reactants and products are comparably abundant

ΔH < 0, ΔS > 0, ΔG < 0

spontaneous at all T’s

ΔH < 0, ΔS < 0, ΔG is T dependent

spontaneous at low T’s

ΔH > 0, ΔS > 0, ΔG is T dependent

spontaneous at high T’s

ΔH > 0, ΔS < 0, ΔG > 0

nonspontaneous at all T’s

solubility of a compound

the amount of the compound that dissolves in a specified volume of solution

molar solubility

the number of moles that dissolves to give one liter of saturated solution (Moles/L)

K expression does not contain

(s) or (l)

Ksp

tells us how insoluble a salt is

the smaller the Ksp, the ___ insoluble the salt

more

the higher the Ksp, the ___ the solubility

greater

Qsp < Ksp

forward reaction favored; no precipitation

Qsp = Ksp

solution is just saturated

Qsp > Ksp

reverse reaction favored; precipitation occurs

any salt containing an anion that is the conjugate base of a weak acid will dissolve in water to a greater extent than given by Ksp

F^-, OH^-, S^2-, CO₃^2-, CN^-, PO₄^3-

fractional precipitation

the method of precipitating some ions from a solution while leaving others in solution

two insoluble compounds with a 1:1 ion ratio contain the same ___ and have a Ksp that differs by ___

cation, 10⁴

if a solution contains Cu⁺, Ag⁺, and Au⁺, each ion can be precipitated as ___

chlorides

ligands

molecules or ions that bind to metal ions; Lewis bases that form “coordinate covalent bonds” with the metal

examples of ligands

H₂O, NH₃, CN^-

Kf

an equilibrium constant measuring the strength of the interaction between a metal ion and ligands to form a complex ion in solution

a ligand ___ the solubility of a slightly soluble ionic compound if it forms a complex ion with the cation

increases

buffers

resists pH change by neutralizing added acid or added base

buffer contains either…

1. significant amounts of a weak acid and its conjugate base or

2. significant amounts of a weak base and its conjugate acid

common ion effect

occurs when a solution contains two solutions that share a common ion, shifting equilibrium toward the reactant and reducing solubility compared to pure water

buffer capacity

how much added acid or base it can effectively neutralize

buffer range

the pH range over which a particular acid and its conjugate base can be effective

solutions that contain a weak acid plus a salt of the weak acid are always less ___ than solutions that contain the same concentration of the weak acid alone

acidic

solutions that contain a weak base plus a salt of the weak base are always less ___ than solutions that contain the same concentration of the weak base alone

basic

equivalence point

the point at which the reaction is complete (moles of acid = moles of base)

end point

the point at which the indicator changes color

half-equivalence point

occurs when half ot eh acid or base has been neutralized

equivalence point of a strong acid/strong base titration

pH = 7

equivalence point of a strong base/strong acid titration

pH = 7

equivalence point of a weak acid/strong base titration

pH > 7

half-equivalence point of a weak acid/strong base titration

pH = pKa

equivalence point of a weak base/strong acid titration

pH < 7

half-equivalence point of a weak base/strong acid titration

pOH = pKb or pH = 14 - pKb

if [ln^-]/[Hln] = 1 or pH = pKa, the indicator solution will be ___ in color

intermediate

if [ln^-]/[Hln] > 10 or pH > pKa, the indicator solution will be the color of ___

ln^- (color 2)

if [ln^-]/[Hln] < 0.1 or pH < pKa, the indicator solution will be the color of ___

Hln (color 1)

melting

endothermic

freezing

exothermic

vaporization

endothermic

condensation

exothermic

sublimation

endothermic

if Ka > Kb…

pH < 7

if Ka < Kb…

pH > 7

if Ka = Kb…

equivalence point at pH = 7