EXAM 2 REVIEW

Define this

100

Define Bond Strength

Energy to break bonds

200

Define Equilibrium

equilibrium is when the forward and reverse rate if reaction are equal.

300

Compare Kc and Kp

Kc = [C]^c[D]^d / [A]^a[B]^b

Kp = (P_C)^c(P_D)^d / (P_A)^a(P_B)^b

400

Define what it means to be an a chemistry student

yeah..... i ran out of stuff (or did I.. dun Dun DUUUNN!!!)

500

What is a van't Hoff factor?

represents the number of dissociation of a compounds when dissolved (usually in water)

van't Hoff

100

Identify the solute with the highest van't Hoff factor.

A) nonelectrolyte  

B) KI  

C) MgSO4  

D) CaCl2  

E) AlCl3

E) AlCl3

200

Identify the solute with the lowest van't Hoff factor.

A) nonelectrolyte

B) KI

C) MgSO4

D) CaCl2

E) AlCl3

A) nonelectrolyte

300

Choose the aqueous solution below with the highest freezing point. These are all solutions of nonvolatile solutes and you should assume ideal van't Hoff factors where applicable.

A) 0.200 m Mg(ClO4)2

B) 0.200 m Na3PO3

C) 0.200 m HOCH2CH2OH

D) 0.200 m Ba(NO3)2

E) These all have the same freezing point

C) 0.200 m HOCH2CH2OH

400

Which of the following compounds has a van’t Hoff factor a 4? Select all that apply.

NaHCO3

Na2SO4

FeBr3

AlCl3

NH4HSO4

FeBr3

AlCl3

500

Which of the following is the van’t Hoff factor of the ionic compound CH3COONa

1

2

3

4

2

It's Hot and It's Cold

100

Write the Equation for Freezing Point Depression and Boiling Point Elevation

Freezing point depression: (delta)Tf = i(Kf)m

Boiling Point Elevation: (delta)Tb = i(Kb)m

200

When 20.0 grams of an unknown nonelectrolyte compound are dissolved in 500.0 grams of benzene, the freezing point of the resulting solution is 3.77 °C. The freezing point of pure benzene is 5.444 °C and the Kf for benzene is 5.12 °C/m. What is the molar mass of the unknown compound?

Answer: Molar mass = 122.34g/mol

Use (delta)Tf = i(Kf)m equation,

then given grams/ found moles = Molar Mass

300

What is the freezing point of a solution of ethyl alcohol, that contains 20.0 g of the solute (C2H5OH), dissolved in 590.0 g of water? Kf for water is 1.86 °C/m.

Answer: delta Tf solution = -1.37*C

400

How many grams of pyrazine (C4H4N2) would have to be dissolved in 1.50 kg of carbon tetrachloride to lower the freezing point by 4.4 °C? The freezing point constant for carbon tetrachloride is 30. °C/m.

 Answer: grams of pyrazine = 17.62g

500

What is the boiling point elevation when 11.4 g of ammonia (NH3) is dissolved in 200. g of water? Kb for water is 0.52 °C/m.

Answer: delta Tb = 1.74*C

Rate of Rxn

100

Calculate the rate at which B and C are formed if A is consumed at 3.6x10^-4 M/s

   2A → 4B + C 

B=1.8x10^-4 M/s C = 7.2x10^-4 M/s

200

The half-life of cobalt-60 is 5 years. If you have 10 grams of Co-60, how much do you have after 15 years?

A: 1.25g

300

Americium-242 has a half-life of 6 hours. If you started with 24g and you now have 3g, how much time has passed?

A: 18 hours

400

Calculate the rate constant at 35*C for the hydrolysis of sucrose given that the rate constant is equal to 1x10^-3 M-1s-1 at 37*C. The Ea = 108KJ/mol.

Ln(K2/K1) = Ea/R * (1/T1 - 1/T2)

   Ln(1x10^-3 / K1) = 108000/8.314 * (1/308 - 1/310)

   K1 = 0.000761 = 7.62 x 10^-4M-1s-1

500

2 NOBr (g) → 2 NO (g) + Br2 (g)

is a second order reaction with respect to NOBr. k = 0.810 M-1⋅s-1 at 10o C. If [NOBr]o = 7.5 × 10-3 M, how much NOBr will be left after a reaction time of 10 minutes? Determine the half-life of this reaction.

A: 1.6x10^-3M after 10 mins; t(½) ~ 160s

 http://www.csus.edu/indiv/m/mackj/chem142/kinetics.pdf 

Equilibrium

100

 For the following reaction, 2 SO2(g) + O2(g) ⇆ 2 SO3(g), the equilibrium constant at 727*C is 261. Calculate the equilibrium constant for the following reactions.

a) 2 SO3(g) ⇆ 2 SO2(g) + O2(g)

b) SO2(g) + ½ O2(g) ⇆ SO3(g)

a) 2 SO3(g) ⇆ 2 SO2(g) + O2(g)

~ reversed the initial reaction

Kc = (1/261) = 0.00383

b) SO2(g) + ½ O2(g) ⇆ SO3(g)

~ multiply the coefficients by ½

Kc = (261)^(½) = sqrt(261) = 16.2

200

T/F: the equilibrium constant formula only includes gases

False, also includes aqueous solutions

300

T/F: Kc can rarely be found with math without having done an experiment

False - K cannot be found without having done an experiment

400

The equilibrium constant for the reaction shown here is Kc =200. A reaction mixture at equilibrium contains [H] = 25M and [H2O] = 0.15M. What is the concentration of O2 in the mixture?

4H + O2 ⇆ 2H2O

~Kc = [H2O]^2 / ([H]^4)([O2])

[O2] = [H2O]^2 / ([H]^4)Kc = 2.88x10^-10M

500

Use the data to find the equilibrium constant (Kc) for the reaction A(g) ⇆ 2B(g) + C(g)

  A(g) ⇆ 2X(g) + C(g) Kc1 = 1.78

  B(g) ⇆ X(g) Kc2 = 23.6

~ nothing changes with the first reaction. The second reaction is reversed and multiplied by coefficient of 2.

  A(g) ⇆ 2X(g) + C(g) Kc1 = 1.78

  2X(g) ⇆ 2B(g) Kc2 = (1/23.6)^(2) = 0.001795

Kc = 1.78 x 0.001795 = 3.2x10^-3

(from 3.01.18)