Exam 2 Jeopardy!

Thermodynamics

100

These laws state that energy can only be converted from one form to another, and that the disorder of the universe is always increasing for all spontaneous processes.

What are the first and second laws of thermodynamics.

200

If enthalpy<0 and entropy<0, would you expect the reaction to be spontaneous?

Spontaneous at low temps, non-spontaneous at high temps

300

The volume of 0.100 mol of helium gas at 27°C is increased isothermally from 2.00 L to 5.00 L. Assuming the gas to be ideal, calculate the entropy change for the process.

ΔSgas = 0.100 mol (8.314 J/mol-K) ln(5.00L/2.00L) = 0.762 J/K

400

Calculate the value of ΔS when 1.00 mol of CH3OH(l) is vaporized at 64.7°C. Normal boiling point=64.7oC, and its molar enthalpy of vaporization is ΔHvap = 71.8kJ/mol.

71800J/(64.7 + 273.15)K = 213 J/K

500

Calculate the ΔH°, ΔS°, and ΔG° of the following reaction: 2CH3OH(g) + H2(g) -> C2H6(g) + 2H2O(g). ΔH°(CH3OH, g) = -201.2 kJ/mol, ΔS°(CH3OH, g) = 237.6 J/mol-K, ΔG°(CH3OH, g) = -161.9 kJ/mol ΔH°(H2, g) = 0 kJ/mol, ΔS°(H2, g) = 130.58 J/mol-K, ΔG°(H2, g) = 0 kJ/mol ΔH°(C2H6, g) = -84.68 kJ/mol, ΔS°(C2H6, g) = 229.5 J/mol-K, ΔG°(C2H6, g) = -32.89 kJ/mol ΔH°(H2O, g) = -241.82 kJ/mol, ΔS°(H2O, g) = 188.83 J/mol-K, ΔG°(H2O, g) = -228.75 kJ/mol

ΔH° = 2(-241.82) + -84.68 – (0 + 2*-201.2) = -165.92 kJ ΔS° = 2(188.83) + 229.5 – (130.58 + 2*237.6) = 1.38 J/K ΔG° = 2(-228.57) + -32.89 – (0 + 2*-161.9) = -166.23 kJ

Aqueous Equilibirum

100

You add a little bit of sodium acetate to an acetic acid solution. How would you expect the addition to affect the equilibrium of acetic acid (HC3H3OO→←H++C3H3OO-)?

You would expect equilibrium to shift to the left, favoring the protonated acid due to the increase in C3H3OO- in solution.

200

Will KC3H3OO be more or less soluble in HCl than in water?

It will be more soluble because the acetate ion is slightly basic and will therefore react with the acidic hydrogen in HCl.

300

Ka=6.8*10-4 for HF. What is the pH of a solution that is 30mL 0.01M HF and 30mL 0.01M NaF?

x(x+0.005)/(0.005-x)=6.8*10-4

400

How many moles of NaHCO3 and Na2CO3 are required to prepare 1.00 L of a buffered solution with pH = 9.50 and a total concentration of carbonate and hydrocarbonate 0.100 M; Ka=5.6·10-11?

0.0849mol CO32-; 0.0151mol HCO3-

500

For H5IO6, Ka1 = 2.8·10-2, Ka2 = 5.3·10-9. What is the pH of a 0.01M H5IO6 solution after 0.01mol NaOH has been added?

pH=4.91

Acid/Base Chemistry

100

Water is technically a weak acid. Would you be able to titrate water with a very strong base? Why or why not?

You would not be able to, because Ka for water is less than 10-8

200

You have 300mL of 0.01M HCl solution. How much 0.05M NaOH solution do you need to reach the equilibrium point?

6.0mL

300

You have 300mL of 0.01M HCl solution. What is pH of the solution after you have added 3.0mL of 0.05M NaOH?

3.31=pH

400

You have a 300mL of 0.01M acetic acid solution (Ka=1.8*10-5). What is the pH at the equilibrium point?

(x2)/(0.001-x)=Kb

500

You have 300mL of 0.01M acetic acid solution (Ka=1.8*10-5). What is the pH after you have added 5.0 mL of 0.05M NaOH?

pH=4.05

Solubility

100

Why is CaCO3 more soluble in water than you would predict from tabulated values?

CO32- is slightly basic, so it can react with water; the anion and cation can also form ion pairs

200

If the molar solubility of CaF2 at 35oC is 1.24 * 10-3 mol/L, what is the Ksp at this temperature?

Ksp = 7.63 * 10-9

300

Will Ag2SO4 (Ksp = 1.5 * 10-5) precipitate when 100 mL of 0.050M AgNO3 is mixed with 10 mL of 5.0 * 10-2 M Na2SO4 solution?

Q < Ksp -> no precipitation

400

Calculate the concentration of Cu2+ in 1.0 L of a solution that contains a total of 1 * 10-3 mol of copper(II) ion and that is 0.10M in NH3. (Cu(NH3)42+ Kf = 5 * 1012)

[Cu2+] = 2 * 10-12 M

500

The Ksp of Ba(IO3)2 at 25oC is 6.0 * 10-10. What is the molar solubility of Ba(IO3)2?

5.3 * 10-4 mol Ba(IO3)2/L

Misc.

100

What does it mean when G>0, G<0, and G=0?

G>0; reverse process is spontaneous and is the amount of work necessary for the forward reaction to occur; G<0, forward process is spontaneous and can do work, G=0, process is at equilibrium and no work can be obtained.

200

When CH3OH(l) is at its normal boiling point, does its entropy increase or decrease?

Goes from (l) -> (g) – entropy increases

300

Will Ca(OH)2 (Ksp = 6.5 * 10-6) precipitate from solution if the pH of a 0.050M solution of CaCl2 is adjusted to 8.0?

Q < Ksp -> no precipitation

400

A solution contains 0.05 M Ba2+; Ksp(BaSO4) = 1.1·10-10; how much SO42- is needed to precipitate out the Ba2+?

2.2*10-9M

500

Calculate the solubility of Mn(OH)2 (Ksp =1.6 * 10-13) in grams per liter when buffered at pH 7.0.

1.4 * 103 g/L