Intermolecular Forces
What is the difference between intramolecular forces and intermolecular forces?
- intermolecular = between MOLECULES
- intramolecular = within molecules/between ATOMS
What is k?
rate constant
- can be solved for using rate law or it may be given
In GENERAL what is K?
Equilibrium constant
- concentration of products over reactants raised to their exponents
Set up an ICE table for the following scenario
What is the pH of 0.672 [HCl]?
HCl is a strong acid so 0.672=[H+]
So this is a trick question no ICE table is needed
- simply take the -log of 0.672 to find the pH
What is the formula for molarity and molality?
Molarity = M = mol solute/L solution
Molality = m = mol solute/kg solvent
What is the strongest type of intermolecular forces?
Hydrogen bonds
- ie. between water molecules
- occur due to polarity
Name two factors that can impact the rate of the reaction
- concentration: the more particles in the system, the more likely it is for the particles to collide and participate in a reaction
- temperature: the faster the particles are moving, the more likely it is for the particles to collide and participate in a reaction
What does it mean for a reaction to be at equilibrium?
the rate of "forward" reaction is equivalent to the rate of "backward" reaction
- forward = reactants -> products
- backward = products -> reactants
Set up an ICE table for the following scenario
What is the pH of 0.75 [HF]?
*you would be given the Ka to actually solve the problem*
HF is a weak acid
HF + H2O -> H+ + F-
I 0.75. _ 0. 0
C. -x. _. +x. +x
E. 0.75-x. _. x. x
What is one example of a colligative property?
Any physical property that is impacted by the solubility of the solution
- osmotic pressure -> pi=MRT
- vapor pressure -> delta P = Xsolute x P*solvent
- freezing point -> change in fp = iKfm
- boiling point -> change in bp = iKbm
What is the weakest type of intermolecular force and between what type of molecules do these occur?
*the type of force has multiple names*
London Dispersion/Van Der Waals Forces
- occur between nonpolar covalent molecules
ie. CH3CH2CH3 & CH3
What is the general formula for rate law?
Rate=k[A]^m[B]^n
- A and B are the reactants
- n and m are the coefficients within the chemical equation
moles OH- = moles H+
What is the Hendersnn Hasselbalch equation?
*yes that's really how you spell it lol*
used to find the pH of weak acids
- often used for buffer solutions
pH=pKa + log [base]/[acid]
What is the most important thing to remember about the behavior of STRONG acids and bases?
they fully dissociate into ions in water so the initial molarity of the solution = [H+/OH-]
Which of the following combinations will have the highest solubility?
a) CH3OH in H2O
b) HCl in H2O
c) MgCl2 in CH3CH2OH (ethanol)
a because both of these molecules are polar and "like dissolves like"
- in b and c there is an ionic solute in a polar covalent solvent
*remember H2O is the universal solvent*
If the rate is first order with respect to a given reactant, what does that mean?
- if the concentration doubles, the rate doubles
- if the concentration quadruples, the rate quadruples ect.
What is Kw?
Kw = 1.0 x 10^-14 = [H+][OH-]
Set up an ICE table for the following scenario
What is the pH of the following titration rxn: 30.0mL of 0.100 [NaOH] is added to 40.0mL of 0.100 [CH3COOH]?
solve for moles of CH3COOH and OH-
0.100M x 0.030L = 0.003mol
0.100M x 0.040L = 0.004mol
CH3COOH + OH- -> H2O + CH3COO-
0.004 0.003. _. 0
- 0.003 -0.003 _. + 0.003
0.001 0. _ 0.003
- you would be given the Ka
pH = -logKa + log [0.003]/[0.001]
What is Van't Hoff factor (i)?
a variable used in colligative properties to express the number of ions that a solute will dissolve into in solution
- normally 1 because we usually are working with covalent compounds
Which of the following molecules will exhibit stronger intermolecular forces and therefore have a higher bp and lower fp?
CH3NH2 or CH3F
CH3NH2 because it can make H bonds with itself since there are hydrogens bonded to N
- the strongest bonds CH3F can form is dipole-dipole
- also remember that molecules with a higher molar mass will have higher bp and lower fp because there are more opportunities for bonding in larger molecules
rate=k[NO2][O2]
this is a second order rxn so the integrated rate law is ... 1/[At] = kt + 1/[Ao]
Ammonia (NH3) has a Kb of 5.9 x 10^-4. What is the pH of 1.50M solution of NH3?
1. Is NH3 an acid or base?
2. Is it weak or strong?
NH3 is a weak base b/c it doesn't have OH
NH3 + H2O -> NH4+ + OH-
I 1.5. - 0. 0
C. -x. - +x. +x
E. 1.5-x. _. x. x
0.00059 = x^2 / 1.5 (make the assumption)
x^2 = .000885
x = 0.0297 = [OH-]
pOH = -log(0.0297) = 1.53
pH = 14 - 1.53 = 12.5
Set up an ICE table for the following scenario
PbF2 is shaken with H2O at 25*C and the solubility= 0.64g/L. What is the Ksp of the solution?
PbF2 -> Pb^2+ + 2F-
__. 0. 0
__ +x. +2x
__. x. 2x
Ksp=[Pb^2+][F-]^2
0.64g x 1mol/245.2g = 0.00261mol = [Pb^2+]
F- = 2(0.00261) = 0.00522
Ksp=[0.00261][0.00522]^2 = 7.1 x 10^-8
What is entropy?
the disorder with a substance
ie. the entropy of a gas will be much higher than a solid because the particles are moving much faster and therefore their movement is much less predictable