Colligative Properties
When the concentration of solute INCREASES, what happens for each property?
Freezing point depression, Boiling point elevation, Vapor pressure, Osmotic pressure
Freezing point depression (FP lowers)
boiling point elevation (BP raises)
vapor pressure (VP lowers)
osmotic pressure (π increases)
What are the units of k when the overall reaction order is 2?
M-1 time-1
Using the following reaction, if the rate of appearance of H2O is 0.0034 M/s, what is the rate of disappearance of O2?
C3H8 + 5O2 → 4H2O + 3CO2
0.00425 M/s
What sign is S for the following process?
4Fe(s) + 3O2(g) --> 2Fe2O3(s)
Negative
Place these liquids in order of increasing solubility in water. dimethyl ether (CH3OCH3), propane (C3H8), ethanol (CH3CH2OH)
propane < dimethyl ether < ethanol
Rank from LOWEST TO HIGHEST for vapor pressure of water:
A 1 mole of CH3OH in water
B 1 mole HCl in water
C 1 mole Mg(NO3)2 in water
C < B < A
A reaction has a half-life of 0.32 min. How long will it take the reaction to have 3.13% left?
1.6 minutes
100 - 50 - 25 - 12.5 - 6.25 - 3.125 = 5 half lives
5 * 0.32 = 1.6 min
Given the rate law:
RATE = k [red dye][OCl-]
What plot vs. time would yield a linear plot for red dye?
ln [red dye] vs. time
1st order in red dye.
Given the reaction:
A + 2B --> C
And the following ∆Gºf values (kJ/mol):
24.2 33.0 173.4
What is ∆Gºrxn? Is it spontaneous?
+83.2 kJ/mol
Non-spontaneous
This water treatment method applies pressure in order to purify water aboard ships
Reverse Osmosis (RO)
What is the Kb of a solvent, given that when in a 3.0 molal solution, the change in boiling point increases by 5.15ºC?
1.72 ºC/m
Given the reaction A-->B,
and k=0.28s-1; [A]0=0.42 M
What is [A]t=24s?
5.067E-4 M
The reaction A + 2 B → C has the rate law:
rate = k[A][B]
By what factor does the rate of reaction increase when both [A] and [B] are doubled?
4x
Given a reaction at 298K, A + B --> C,
∆Hºrxn = +27.4 kJ/mol;
∆Gºrxn = -42.8 kJ/mol
What is ∆Sºrxn?
+236 J/molK
What must the signs of ΔH and ΔS be if a reaction is spontaneous at all temperatures?
∆H negative
∆S positive
What is the molality of an aqueous solution, if the new freezing point is -3.8ºC? Kf of water = 1.86ºC/m
2.04 m
If k=0.040M-1s-1 and given
[A]t=23s= 0.20M, the initial concentration for the reaction A-->B is?
0.245 M
Trial [A] (M) [B] (M) Initial rate (M/s)
1 [0.020] [0.010] [0.050]
2 [0.020] [0.020] [0.100]
3 [0.060] [0.020] [0.900]
What is the overall order of reaction?
RATE = k [A]2[B]
Overall order = 2 + 1 = 3
Calculate ΔS°sxn (T = 298K and P = 1 atm) for the synthesis of N2O + NO2 ⟶ 3 NO if the rxn is at equilibrium.
The standard enthalpies (∆Hfº) for the compounds are
N2O = 87 kJ/mol, NO2 = 54 kJ/mol, and NO = 92 kJ/mol
∆Hºrxn = products - reactants = 135 kJ/mol
∆Gº = ∆Hº - T∆Sº ==> ∆S = ∆H/T
∆Sº = 135000/298 = 453 J/K
What does sarin bind to when it acts as a nerve agent?
acetylcholinesterase - the enzyme that allows acetylcholine to break down, which prevents muscles from relaxing.
A 0.55 g sample of a non-electrolyte is dissolved in 5.31 g of lauric acid (Kf = 3.9ºC/m). The freezing point depression is determined to be 4.20ºC. What is the molar mass of this compound?
96.2 g/mol
What is Ea given the reaction
A-->B,
k1=4.75E-4 s-1 at 290K
k2=1.63E-3 s-1 at 303K
69.2 KJ/mol
Trial [A] (M) [B] (M) Initial rate (M/s)
1 [0.020] [0.010] [0.050]
2 [0.020] [0.020] [0.100]
3 [0.060] [0.020] [0.900]
What is the rate constant k?
12,500 M-2s-1
Below what temperature does the following reaction become nonspontaneous?
2HNO3(aq) + NO(g) → 3NO2(g) + H2O(l)
ΔSºrxn = 287.5 J/molK
ΔHºrxn = 136.5 kJ/mol
474.8 K
How does distillation work?
Heat water to evaporate it and then collect the condensed pure water