Lewis Structures & Enthalpy Change Exercises

Topics being Covered in the Worksheet:
1. Lewis Structures
2. Bond Order, Bond Length, and Bond Energies
3. Enthalpy Change via Bond Energy
4. Polarity
5. VSEPR
6. Formal Chargeshe questions include tables to fill them the worksheet

Instructions for Working out the Worksheets:

Work in groups of 4 on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help. Your TA will come around when needed to help guide you if needed.

Round Robin Instructions:

  1. Each group member will be assigned a number, starting with #1 and ending with the number of people in the group.
  2. Student #1 will read the question aloud and define the information needed to solve the problem, create an outline on how you can solve the problem.
  3. When the group agrees that the necessary information is complete, student number two will do the first step. When the group agrees that the step is correct, student number three will do the next step. Continue this way until the group agrees that the given answer had been correctly drawn and identified.
  4. Student #2 will start the next question by reading it aloud as in #1. Follow this pattern for all the questions in the session.

Topics being Covered in the Worksheet:

1.     Lewis Structures

2.     Bond Order, Bond Length, and Bond Energies

3.     Enthalpy Change via Bond Energy

4.     Polarity

5.     VSEPR

6.     Formal Charges

  1. Complete the table which will go over topics 1 and 2. Using the covalent radii table.

Molecule

Lewis Structure

Bond of

Interest

Bond

Order

Bond

Length

Bond

Energy

(kJ/mol)

H2H-H436
Cl2Cl-Cl243
H2OO-H464
H3CCH3C-C346
H2CCH2C-C615

H2CCH 2

Molecule

Lewis Structure

Bond

C-C of

Interest

Bond  

Order

Bond  

Length

Bond

Energy 615

(kJ/mol)

HCCHC-C835
CO2C-O804
H2COC-O799
N2N-N945
O2O-O498
  1. In the following problems you will be solving mathematical problems to help you understand topic 3. Make sure you have the correct significant figures for each problem

 

Average Bond Energies (kJ/mol)

H–H436 kJ/molC–H413 kJ/molC=C614 kJ/mol
H–Cl431 kJ/molC–C348 kJ/molC!C839 kJ/mol
H–F567 kJ/molC–N293 kJ/molC=O799 kJ/mol
N–H391 kJ/molC–O358 kJ/molO=O495 kJ/mol
N–O201 kJ/molC–F485 kJ/molC!O1072 kJ/mol
O–H463 kJ/molC–Cl328 kJ/molC=N615 kJ/mol
O–O146 kJ/molC–S259 kJ/molN=N418 kJ/mol
F–F155 kJ/molCl–Cl242 kJ/molN!N941 kJ/mol
C!N891 kJ/mol

Estimate the enthalpy change (!Hrxn) of the following reactions using the bond energies above.

                                                                                         Cl                            O

 

1.             H H + Cl Cl ! H Cl + H Cl

H H

   4.          H C Cl + O !                   C Cl +

Cl                                 Cl

H

H Cl

2  .        HH  C C HH  + F F ! H CF  CF  H                     5.       H CH  H + OO  OO  !  O C O +    HH  OO  HH

                       H H                              H       H

  1. H C O H + H C O H ! H C O C H + H O H

                       H H                                  H       H

  1. In the following problems you will be determining which is most polar and explain the reasoning for the choice, to help you understand topic 4.
    • carbon disulfide                  OR             sulfur difluoride
  • nitrogen trichloride    OR             oxygen dichloride
  • boron trihydride          OR             ammonia
  • chlorine                   OR             phosphorus trichloride
  • silicon dioxide          OR             carbon dioxide
  • methane                  OR             CH2Cl2
  • silicon tetrabromide   OR             HCN
  • nitrogen trifluoride     OR             phosphorus trifluoride

 

  1. In the following problems draw and name the Lewis structure and VSPR structure of the following. This will help with topics 1 and 6.
MoleculesLewis Structure & NameVSEPR Structure & NameFormal

Charge of

Central Atom

H2CS
N2O5
BF3
NO2-
CCl4
PF5
ICl3
XeF2
MoleculesLewis Structure & NameVSEPR Structure & NameFormal

Charge of

Central Atom

ClF5
SF6
XeF4
BrF5
XeCl3
C2H6O
C6H6

(C’s form a ring)

CH2O
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