Gen Chem 2: Chapters 12/13

saturated solution

maximum amount of solute

unsaturated solution

less solute than solvent

supersatured solution

more solute than saturated solution (max solute)

crystalization

process of solute coming out of solution as crystal, formation of pure solid

precipitation

same as crystallization (forming pure solids), but solute may not be crystallized (amorphous - non ordered)

exothermic (- delta H solution)

solute/solvent formation interaction > solute/solute + solvent/solvent broken interactions

endothermic (+ delta H solution)

solute/solvent formation interaction < solute/solute + solvent/solvent broken interactions

entropy

disorder; driving force toward a more random state

enthalpy

attractive forces between solute and solvent, like dissolves like and similar IMFs

miscible/imissible

ability to dissolve or not

solvation

process of solute dissolving - solute becoming surrounded by solvent molecules

shorter non polar chain

more soluble in H2O

% by mass

(mass of solute / mass of solute + solvent = solution) x 100 =

mole fraction (X)

moles of A / sum of moles of all components

molarity (M)

mol solute / L solution - temperature dependen

molality (m)

mol solute / kg solvent - temperature independent

solubility of solids increases (not all solids)

temperature increases

fractional crystalization

separating mixtures based on different solubilities - given amount needs to be less than graph amount to be soluble

solubility of gases decrease

temperature increases

henry’s law

gas solubility = pressure, so as pressure increases so does a gas’s solubility

colligative properties

only depend on amount of solute, not on the nature of solute properties

types of colligative properties

vapor pressure (lowering), boiling point elevation, freezing point depression, osmotic pressure

vapor pressure lowering

pressure exerted on a liquid, VP of a solution is always LOWER than the pure solvent

Raoult’s Law

P1 = X1 P1º

• P1: VP of solution

• X1: mole fraction of solvent

• P1º: VP of pure solvent

change in VP equation

Delta P = X2 P1º

• Delta P: change in VP

• X2: mole fraction of another species

• P1º: VP of pure solvent

Raoult’s Law for Volatile Mixtures - IDEAL

PT = XA PAº + XB XPº

• PT = total pressure

• XA/B = X mole fraction

• PA/Bº = given pressure of pure solvent

fractional distilation

separating liquid based on different boiling points

boiling point elevation

increase in BP when solute is added to solvent

BP elevation equation

Delta Tb = iKbm

• Delta Tb: change in BP

• i = Van’t Hoff factor, based on # of ions, 1 for molecular compounds

• Kb = molal BP elevation constant

• m = molality

  • pure solvent BP (100º for H2O) + Delta Tb = solution BP

freezing point depression

solution always less than pure solvent

FP depression equation

Delta Tf = iKfm

• Delta Tb: change in FP

• i = Van’t Hoff factor, based on # of ions, 1 for molecular compounds

• Kf = molal FP depression constant

• m = molality

  • pure solvent FP (0º for H2O) - Delta Tf = solution FP

osmotic pressure (pi)

pressure required to stop osmosis; at constant temp, pi is proportional to molarity

osmotic pressure equation

pi = iMRT

• pi: osmotic pressure

• i = Van’t Hoff factor, based on # of ions, 1 for molecular compounds

• M = molarity

• R = gas constant; 0.0821 atm/K mol

• T = temp in K

colligative properties of electrolyte solutions

must account for dissociation of solutes as well - use i measured (given) instead of calculated

colloid dispersions

• colloidal particles much larger than solute molecules

• colloidal suspension is not as homogenous as a solution

• Tyndall effect - scattered light through particles

chemical kinetics

change in concentration of reactants/products over time

reaction rate

the change in concentration with time (M/s or mol/Ls or mol L-1 s-1); can be - Delta [reactants] / Delta t OR Delta [products] / Delta t

initial rate

t = 0

instantaneous rate

t = x

average rate

slope

homogenous reaction

reactants in different phasesh

heterogenous reaction

reactants all same phase

concentration increases OR temperature increases

rate increases

coefficients in reaction rates: aA → bB

rate = -1/a Delta [A] / Delta t = 1/b Delta [B] / Delta t

a species is reacted at a rate of X M/s; given chemical equation

use stoich with reaction rate and mole ratios of the two species

rate law of aA + bB → cC + dD

rate = k[A]^x[B]^y

x + y exponents

• found experimentally

• usually small integers (1, 2, 0)

• x = order of the rxn with respect to A

• NOT THE COEFFICIENT

finding units of k

reorder rate law to single out k, substitute with units (rate = M/s, [ ] = M) and raise to the power if needed

initial rates to find rate law

• given data set

finding order of species:

• choose two experiments - if finding order of X, choose where X is changing and Y is staying constant

• rate 2 / rate 1 = eq for rate 2 / eq for rate 1 and substitute with given concentrations

• repeat for other species

finding k: plug in experiment with rate and concentrations and use solved orders

integrated rate laws

graph given, zero/1st/2nd order

zero order k units

M/s or Ms-1

zero order integrated rate law

[A]t = -kt + [A]0

zero order straight line plot

[A]t vs. t

zero order and 1st order slope

slope = -k

zero order half life

t1/2 = [A]0 / 2k

1st order k units

1/s or s-1

1st order integrated rate law

ln[A]t = -kt + ln[A]0

1st order straight line plot

ln[A]t vs t

1st order half life

t1/2 = 0.693/k

2nd order k units

1/Ms or M-1s-1

2nd order integrated rate law

1/[A]t = kt + 1/[A]0

2nd order straight line plot

1/[A]t vs t

2nd order slope

slope = +k

2nd order half life

t1/2 = 1/k[A]0

integrated rate law example

• you will collect [A] vs. time

• you will manipulate [A] into ln [A] and 1/[A] to see which one is straight

• then solve for k or half life from there

collision theory of chemical kinetics

the rate of rxn depends on the frequency of effective collisions (why rate increases with concentration)

activation energy (Ea)

the minimum energy required to initiate rxn; differance between transition state and reaction

Delta H rxn

difference between product and reactant

exothermic graph

- Delta H rxn, heat goes out, more REACTANTS than products

endothermic graph

+ Delta H rxn, heat goes in, more PRODUCTS than reactants

arrhenius equation - dependence of rate constant on activation energy and temp

k = Ae ^ - Ea / RT

• k: rate constant

• A: frequency factor (constant for each system)

• Ea: activation energy (J/mol)

• R: gas constant (8.314 J/Kmol)

• T: temp (K)

linear arrhenius equation

ln k = -Ea/R x 1/T + ln A

• k: rate constant

• Ea: activation energy (J/mol)

• R: gas constant (8.314 J/Kmol)

• T: temp (K)

• A: frequency factor (constant for each system)

arrhenius equation at 2 temps

ln k1/k2 = Ea/R (