Mystery
Which intermolecular forces would be present between an acetate ion and cyclohexane? Select all the apply.
a) Hydrogen bonding
b) dipole-dipole
c) dipole-induced dipole
d) London Dispersion forces
e) ion-induced dipole
c,d,e
Classify a process for which ΔS of the system is negative.
a) Spontaneous
b) reversible
c) impossible
d) not enough info
d) not enough info
Which will favor solubility of covalent compounds?
a) stronger solvent-solvent IMFs
b) stronger solvent-solute IMFs
c) stronger solute-solute IMFs
b) stronger solvent-solute IMFs
What is the value of the can't Hoff factor i for potassium carbonate when it dissolves in water?
a) 1
b) 2
c) 3
4) 4
c) 3
Which of the following will form an ideal solution?
a) C2H5OH and water
b) HNO3 and water
c) CHCl3 and CH3COCH3
d) C6H6 and C6H5CH3
d) C6H6 and C6H5CH3
The bonding interactions among the molecules will be the same strength and type before and after mixing (
A reaction has ΔrG∘ = -2.68 x 104 kJ/mol. How can we best describe this reaction?
a) spontaneous
b) non-spontaneous
c) at equilibrium
d) unknown
d) unknown
Remember that the degree symbol means standard free energy, which only tells us if the reaction favors products or reactants, not whether it is spontaneous or not.
An insoluble salt has a hydration enthalpy greater in magnitude than its lattice enthalpy. What are the signs of standard Gibbs energy, enthalpy and entropy of solution?
ΔG°= +
ΔH°= -
ΔS°= -
What is the freezing point of a solution in degrees C made by dissolving 24.0g of NaCl in 800mL of water?
-1.91 degrees C
Write the equilibrium expression for the following reaction:
HF(aq) + OH-(aq) ⇌ F-(aq) + H2O(l)
K= [F-] / [HF][OH-]
We mix two solvents with identical IMFs types and strengths. What is the value of ΔS of the system and ΔS of the surroundings (positive, negative, zero, or not enough info)?
ΔS universe > 0 (mixing is spontaneous)
ΔH = 0
therefore:
ΔS system > 0
ΔS surroundings = 0
A compound boils at 87∘C and has a heat of vaporization of 59 kJ/mol. Calculate its ΔvapS∘ in kJ/mol K.
ΔvapS∘= 59/332 = 0.178 J/mol K = 178 kJ/mol K
Which molecule would you predict to be the most soluble in water?
a) chloroethane
b) ethanol
c) ethanal
d) ethylene glycol
d) ethylene glycol
Which aqueous solution would be predicted to have the lowest melting point?
a. 0.20 M glucose
b. 0.10 M NaNO3
c. 0.10 M MgO2
d. 0.05 M Na3PO4
c) 0.10 M MgO2
After finishing the Gibb's Free Energy lab, you graph your data. On your graph, you have (1/T) on the x-axis (reciprocal Kelvins) and lnKeq on your y-axis. The equation of the linear fit is y = (8.48 x 103)x -579. Calculate the value of ΔrS∘ and ΔrH∘. Don't forget units!
ΔrH∘= -70.5 kJ/mol
ΔrS∘= -4813 J/mol K
We mix water vapor at 150 degrees C with liquid water at 100 degrees C. Which numbers do we need to calculate the final temperature of the mixture (Select all that apply)?
a) specific heat of liquid water
b) specific heat of water vapor
c) heat of vaporization
d) mass of liquid
e) mass of vapor
b,c,d,e
Which salt will most likely have a negative value for ΔsolutionS∘?
a) NaCl
b) CaCl2
c) MgO
d) Li2S
c) MgO (small radius, big charge)
Which of these salts would be most likely to have a negative value for ΔsolnS∘?
a) CaCl2
b) KCl
c) CaO
d) BaS
c) CaO
Higher charge density --> more negative ΔsolnS∘
Therefore you want big charge, small size
An aqueous solution of CaCl2 boils at 109.3 degrees C. At what temperature will it freeze? Kb(H2O) = 0.512 deg/m. Kf(H2O) = 1.86 deg/m.
-33.8 degrees C
You combine a 106mL solution of 1.75M HClO4 and a 118mL solution of 1.25M Ca(OH)2, both with initial temperatures of 25 degrees C. The change in enthalpy of the reaction is -57.3kJ/mol. To this combined solution, you add 20g of ice at an initial temperature of -50 degrees C. What is the final temperature of the solution?
Tf = 24.8 degrees C
Consider ΔlatticeS∘, ΔsolnS∘, ΔhydrationS∘, and ΔlatticeH∘, ΔhydrationH∘ , and ΔsolutionH∘ for an unknown salt. What are the predicted signs for each of these values (positive, negative, or unknown)?
ΔlatticeS∘ : positive
ΔsolnS∘ : unknown
ΔhydrationS∘: negative
ΔlatticeH∘ : positive
ΔhydrationH∘ : negative
ΔsolutionH∘ : unknown
1. Which molecule would be predicted to have the largest value for ΔvapH∘?
2. Which would be the most soluble in H2O?
3. Which would be the most soluble in benzene?
a) cyclopentane
b) cyclopentanol
c) cyclopentanone
1. b) cyclopentanol
2. b) cyclopentanol
3. a) cyclopentane
A solution of 35.7 g of an unknown organic compound in 220.0g of chloroform has a boiling point of 64.5 °C. What is the molar mass of this compound? The normal boiling point of chloroform is 61.17°C and the Kb=3.80 deg/m.
1.8 × 102 g/mol