Final Exam Review #3
Supplemental Instruction
Iowa State University / Leader: / Allison
Course: / Chem 163
Instructor: / Dr. Appy
Date: / 12/14/14
  1. Define and state the ΔErxn for each:
  2. Exothermic:energy-releasing, ΔErxn < 0
  3. Endothermic:Energy-absorbing, ΔErxn > 0
  4. Use the chart to answer the following questions:

Reaction / Energy of Reactants (kJ/mol) / Energy of Products (kJ/mol) / Energy of Transition State (kJ/mol)
1 / 50 / 60 / 70
2 / 20 / 10 / 90
3 / 10 / 20 / 90
  1. Indicate whether the reactions are endothermic or exothermic.

Reaction 1: Endothermic

Reaction 2: Exothermic

Reaction 3: Endothermic

  1. Determine the value of ΔErxn.

Reaction 1: 60 kJ/mol – 50 kJ/mol = 10 kJ/mol

Reaction 2: 10 kJ/mol – 20 kJ/mol = -10 kJ/mol

Reaction 3: 20 kJ/mol – 10 kJ/mol = 10 kJ/mol

  1. Determine the value of Ea.

Reaction 1: 70 kJ/mol – 50 kJ/mol = 20 kJ/mol

Reaction 2: 90 kJ/mol – 20 kJ/mol = 70 kJ/mol

Reaction 3: 90 kJ/mol – 10 kJ/mol = 80 kJ/mol

  1. In the reaction of X + Y --> Z, the energy of the reactants is 60 kJ/mol, and the energy of the products is 90 kJ/mol. The energy of the transition state is 130 kJ/mol.
  2. Is the reaction endothermic or exothermic?

Endothermic

  1. What is the Erxn?

90 kJ/mol – 60 kJ/mol = 30 kJ/mol

  1. What is the Ea?

130 kJ/mol – 60 kJ/mol = 70 kJ/mol

  1. Catalysts speed up reactions by:
  2. Providing an alternative mechanism for a reaction
  3. Lowering the Ea for the reaction
  4. Remaining active throughout the chemical reaction
  5. All of the above are correct.
  1. The slow step in the mechanism for the production of NO2F from NO2 and F22 is 2NO2 + F2 --> NO2 F + F. Write the predicted rate law for the reaction.

The predicted rate law for the reaction contains the reactants with their respective coefficients as exponents. The predicted rate law is therefore the reaction rate = k[NO2]^2[F2]

  1. Write the equilibrium constant expression for the reaction

H2 (g) + I2 (g) <--> 2 HI (g)

Keq = [HI]^2

[H2]x[I2]

  1. Write the Keq for the following reaction and solve for the Keq with the following concentration at equilibrium
  2. CH4 + 2O2 -> CO2 +2 H2O

0.234 0.20 0.378 0.209

Keq= [0.378] x

[0.234] x [0.20]= 0.35

  1. Using Le Chatelier’s principle:
  1. Concentration
  2. If we increase the concentration of the reactants, which way will the equilibrium switch?To the right/products
  1. If we increase the concentration of the products, which way will the equilibrium switch?To the left/reactants
  1. Will the Keq change?No
  1. Temperature
  2. Which way will the equilibrium switch if we increase the temperature?To the left/reactants
  1. If we decrease the temperature?To the right/reactants
  2. Will the Keq change?YES
  1. Pressure
  2. If we increase the pressure which way will the equilibrium switch?Shift to the side with less moles
  3. If we decrease the pressure?Shift to the side with more moles
  4. Will the Keq change?No
  1. Describe the difference between electrolytes and nonelectrolytes:
  2. Answer the following questions:
  3. Is the compound H2SO4 molecular or ionic?

Molecular

  1. How did you decide on your answer to part (a)?

The formula has no metals in it, just nonmetals.

  1. Based on your answer to part (a), would you call H2SO4 an electrolyte or a nonelectrolyte?

Most molecular compounds are nonelectrolytes

  1. An aqueous solution of H2SO4 causes a light bulb to light. What does this tell you about H2SO4?

If the bulb lights up, it means that it is an electrolyte.

  1. What is the difference between a strong electrolyte and a weak electrolyte?

Strong: completely dissociates into ions upon dissolving in water

Weak: one that only partially dissociates into ions upon dissolving in water

  1. What is the difference between a strong acid and a weak acid?

Strong: water-soluble compound that dissociates extensively in water to give large numbers of H30+ ions

Weak: water-soluble compound that dissociates only partially in water and produces only a few H3O+ ions.

  1. Brønsted-Lowry definition of an acid:

Anything that donates a proton

  1. Brønsted-Lowry definition of a base:

Anything that accepts a proton

  1. In the reaction NH3 + PH3 --> NH2- + PH4+ which reactant is the Brønsted-Lowry acid and which is the base?

Because it accepts a proton, PH3 is the base. Because it donates the proton, NH3 is the acid

  1. Write the formula of the salt formed from the combination of H3PO4 and LiOH.

Anion: PO4 3-

Cation: Li+

Salt: Li3PO4

  1. Calculate the [OH-] in a solution in which [H3O+] = 2.3 x 10^-4

For Hydrogen:

Useful Equations and Constants:

1 mi = 5280 ft

1 in = 2.54 cm

1 mL = 1 cm3

d = m/V

K = ºC + 273.15 ºF = 32 + (9/5)ºC ºC = (5/9)(ºF – 32)

q = mCsΔT

avg. atomic mass = m1f1 + m2f2 + …..

E = hc/λ

c = 3.00 x 108 m/s

h = 6.626 x 10-34 J*s

1 eV = 1.602 x 10-19 J

1 m = 109 nm

F = kq1q2/r2

1 mole = 6.022 x 1023 things

% yield = (actual yield)/(theoretical yield) x 100%

PV = nRT

PiVi/(niTi) = PfVf/(nfTf)

MM = mRT/(PV)

MiVi = MfVf

R = 0.0821 L*atm/(mol*K)

STP = 0 °C and 1 atm

K = °C + 273.15

ΔTf,b = Kf,b x moles of solute / (Kg solvent)

P = F/A

Kw = [H3O+][[OH-] = 10-14

pH = -log[H3O+]