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Sunday, October 13, 2013

Chemistry assignments that use Molecule Calculator (MolCalc)


1. One of the reviewers of our J. Chem. Ed. paper on MolCalc included the following tutorial: Molecular Orbital Calculations of Molecules I.Diatomics, Triatomics and Reactions

2.  n-Butane can exist in two different conformations called gauche and anti (Google butane and conformation).  Use Molecular Calculator to estimate the fraction of molecules in the gauche conformation at 25 C. ΔH  can be computed as the difference in heat of formation.

3. Estimate ΔH  the for the following reaction at 25 C

NH2CHO + H2O NH3 + HCOOH

a. Using bond energies
b. Using Molecule Calculator

4. How does the molecular structure determine the rotational entropy?  Find out by constructing a molecule with the largest possible rotational entropy using Molecule Calculator.  The largest value I could find was 133 J/molK.  Can you beat that?

5. How well do the simple solvation models work?
a. Estimate the solvation energy of NH+4 using MolCalc?
b. What is the polar solvation energy of NH+4 in water at 25 C assuming that it is spherical?

6. Why do ionic compounds dissolve in water?  Use MolCalc to estimate ΔG at 25 oC for the following equilibrium 
 
N(CH3)+4Cl  N(CH3)+4 + Cl

a. in the gas phase
b. in aqueous solution

7. Solvent screening: charge-charge interactions are weaker in aqueous solution than in the gas phase.  Compute the difference in G at 25 C between these two molecules using MolCalc
  
a. in the gas phase
b. in aqueous solution

8. Build a molecule with a solvation energy that is as close to 0 as possible.  The closest I got is -1.3 kJ/  How close can you get? 

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