Exam 3 Review

Review Notes

Keq info

-Large Keq = strong acid or strong base

-Small Keq = weak acid or weak base

-Reverse reaction rate = (1/Keq)

Intramolecular forces

-LDF, dipole-dipole, hydrogen bonding

  • Hydrogen bonding
  • H with N, O, F

Melting point increases with intramolecular forces

pH equations

-pH scale

The only thing that can change the equilibrium constant: changing temperature

Molecular Solids

-Held together by weak intermolecular forces

-London forces (N2), dipole-dipole, H-bonding (H2O)

-Low melting points

Non-molecular Solids

-Held together by chemical bonds

-Ionic (NaCl, 800C), network covalent (diamond, quartz 1700C), metallic (Au)

-High melting points

Strong Acids: HCl, HBr, HI, HNO3, H2SO4

Weak Acids: HF, HClO, CH3COOH, H2CO3, H3PO4

Strong Base: -OH group

Weak Bases: NH3, HCO3-, H2PO4

  1. T / F In general, boiling point increases with polarity.
  2. T / F intramolecular bonds are stronger than intermolecular interactions.
  3. Equilibrium:the forward reaction rate is the same as the reverse reaction rate

Chapter 7

  1. In which of the following are there no dipole-dipole forces between molecules? Explain.

a. AsH3* a, b, and e are all nonpolar (LDF)

  1. CO2

c. H2O*c and d have lone pair electrons and therefore

d. SeCl2 are polar and have dipole-dipole forces
e. SO3

*look at intermolecular forces; all molecular compounds have LDF

  1. Which of the following would you expect to have the highest boiling point? Explain.
  2. Propane, C3H8*a and b are nonpolar (LDF)
  3. Carbon dioxide, CO2
  4. Ethyl alcohol, CH3CH2OH* -OH group = hydrogen bonding
  5. Methyl fluoride, CH3F* polar, dipole-dipole forces
  1. Which of the following do you expect to be nonmolecular solids?
  2. Sodium hydroxide, NaOH* ionic
  3. Solid ethanol, CH3CH2OH
  4. Iron, Fe* metal
  5. Solid silane, SiH4
  1. Arrange these substances in order of increasing melting point: CH3OH, SiO2, C2H6, NaCl.

C2H6 – molecular, nonpolar bonds, LDF

CH3OH – molecular, H-bond

NaCl – ionic solid, nonmolecular (800C)

SiO2 – network covalent solid, nonmolecular (1700C)

Chapter 8

  1. Balance the following equations and classify the reaction they represent as combination, decomposition, single-replacement, or double-replacement:

Fe + CdCl2 FeCl3 + Cd

2 Fe + 3 CdCl2 2 FeCl3 + 3 Cd (single-replacement)

H3PO4 + Ca(OH)2 Ca3(PO4)2 + H2O

2H3PO4 + 3Ca(OH)2 Ca3(PO4)2 + 6H2O (double-replacement)

Chapter 15

  1. Classify each substance as strong electrolyte, weak electrolyte, or nonelectrolyte:
  1. CH3COOHweak electrolyte
  2. KCH3COOstrong electrolyte
  3. H2SO4strong electrolyte
  4. CH2Cl2nonelectrolyte
  5. NH3weak electrolyte
  6. H3PO4weak electrolyte
  7. ZnSO4strong electrolyte
  1. The pH of a solution is -1. What are the H3O+ and OH- concentrations?

[H3O+] = 10 – pH = 10 – (- 1) = 101 = 10 M

[OH-] = 10 – 14 / 10 1 = 10 – 15 M

  1. The [H3O+] concentration of concentrated hydrochloric acid is 12.1 M. What are the pH and OH- ion molar concentration?

pH = - log 12.1 = -(+1.08) = -1.08

[OH-] = 1.0 x 10 – 14 / 12.1 M = 8.26 x 10 – 16 M

Chapter 14

  1. Write the equilibrium constant expression for:
  2. SiCl4(l) + 2 H2O(g)  SiO2(s) + 4 HCl(g)

Keq = [HCl]4 / [H2O]2

  1. H2(g) + CO2(g)  CO(g) + H2O(l)

Keq = [CO] / [H2] [CO2]

  1. TiCl4(g) + 2 Mg(s)  Ti(s) + 2 MgCl2(s)

Keq = 1 / [TiCl4]

  1. Ni(OH)2(s)  Ni2+(aq) + 2 OH-(aq)

Keq = [Ni 2+ ] [OH-]2

  1. The equilibrium constant for the synthesis of methanol,

CO(g) + 2H2(g)  CH3OH(g)

Is 4.3 at 250C and 1.8 at 275C.

  1. Does this reaction shift to the left or to the right when the reaction mixture is heated? Explain how you know.

4.3 at 250C and 1.8 at 275C means that in adding heat the reaction shifts slightly to the left.

  1. Is this reaction endothermic or exothermic? Explain how you know.

Exothermic. The reaction mixture (the products) have a higher temperature than the reactants. By adding heat on the product side, the reaction responds by shifting to the left.

Week 8 Practice Problems

  1. Write the balanced equilibrium equations for the dissociation of phosphoric acid in water.

H3PO4 (aq) + H2O (aq)  H2PO4- (aq) + H3O+ (aq)

H2PO4- (aq) + H2O (aq)  HPO42- (aq) + H3O+ (aq)

HPO42- (aq) + H2O (aq)  PO43- (aq) + H3O+ (aq)

Week 9 Practice Problems

  1. Baking soda (sodium bicarbonate) decomposes when it is heated:

2 NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g) ∆Erxn = 136 kJ/mol

  1. Write the Keq for the above reaction.

Keq = [CO2] [H2O]

  1. Predict if the reaction will shift to the left or right when the reaction is disturbed by the following:
  2. CO2 is removed

It will shift to the right

  1. CO2 is added

It will shift to the left

  1. Reaction is heated

It will shift to the right

  1. An equilibrium mixture at a certain temperature contains 8.3 x 103 M PCl5, 1.5 x 10 -2 M PCl3 and 3.2 x 10 -2 M Cl2. Calculate the equilibrium constant Keq for the reaction:

PCl5 (g)  PCl3 (g) + Cl2 (g)

Keq = [PCl3] [Cl2] / [PCl5]

Keq = (1.5 x 10 -2 M) (3.2 x 10 -2 M) / (8.5 x 103 M) = 5.8 x 10-8