Chem 120 Exams

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unsaturated solution

solution that contains less solute than it has the capacity to dissolve

saturated solution

solution that contains the maximum amount of solute that will dissolve in a solvent at a specific temp

supersaturated solution

solution that contains more dissolved solute than it present in a saturated solution

solution formation

solute dissolves in a solvent to form a solution
to form a liquid solution, the solute needs to separate into individual components, overcome IMF to make room and expand, than allow the solute and solvent to form a solution

predicting solubility for solids

increases with increasing temperature and not affected by increasing pressure

predicting solubility for gases

decreases with increasing temperature and increases with increasing pressure

intermolecular forces

London Dispersal < Dipole-Dipole < Hydrogen Bonding < Ion-Dipole

entropy factors

increasing temperature, volume, number of molecules, and complexity of molecules all increases the entropy of the substance due to microstates

When ∆H is (-) and ∆S is (+)

∆G is (-) so always spontaneous

When ∆H is (+) and ∆S is (-)

∆G is (+) so never spontaneous

When ∆H is (-) and ∆S is (-)

∆G is (-) at low temperatures but (+) at high temperatures

When ∆H is (+) and ∆S is (+)

∆G is (+) at low temperatures but (-) at high temperatures

vapor pressure

proportional to mole faction so it is higher for pure compounds compared to solutions

First Order Reactions

k[A]

k = 1 / s so graph is 1 / s vs T

t_1/2 = ln(2) / k

ln[A] = -kt + ln[A]_o

Second Order Reactions

k[A]²

k = 1 / Ms so graph is 1 / Ms vs T

t_1/2 = 1 / k[A]_o

1 / [A] = kt + 1 / [A]_o

Zeroth Order Reactions

k

k = M / s so graph is M / s vs T

t_1/2 = [A]_o / 2k

[A] = -kt + [A]_o

what step determines the rate of a reaction

slowest step

collision theory

molecules must collide with sufficient energy and in the correct orientation; more concentration, less volume, and higher temperature increases collision

chemical equilibrium

K = products / reactants

ignore solids and pure liquids

Q > K

reaction proceeds spontaneously in the reverse direction or shift left or products to reactants

Q < K

reaction proceeds spontaneously in the forward direction or shift right or reactants to products

Approximation of Reactant Favored

[A]o / Kc > 100

Le Chatelier’s Principle

if a system at equilibrium is distributed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance

Therefore, K only changes with temperature

ΔH > 0

they have a direct relationship so temperature and K increases

ΔH < 0

they have an inverse relationship so temperature increases and K decreases

Increasing reactant concentrations/pressures

denominator increases so Q decreases so Q < K

Increasing product concentrations/pressures

numerator increases so Q increases so Q > K

Increasing overall pressure with an inert gas

Q = K so no shift

Decrease Volume of Container

shift towards the side with less moles

Increase Volume of Container

shift towards the side with more moles

K >> 1

∆G_o < 0 and spontaneous and product favored

Q >> 1

Q is most likely > K and is non-spontaneous in the reverse direction and ∆G > 0

K << 1

∆G_o > 0 and non-spontaneous and reactant favored

Q << 1

Q is most likely < K and is spontaneous in the forward direction and ∆G < 0

Common Ion Effect

the shift in an equilibrium position caused by the addition or presence of an ion involved in the equilibrium reaction

Q < Ksp

solution is unsaturated (more salt will dissolve)

Q > Ksp

The solution is supersaturated (precipitation will occur)

Q = Ksp

The solution is saturated (at equilibrium)