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discussion key 12.6.11

# discussion key 12.6.11 - the expression where n 1,2 is the...

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Discussion Section Problems 12.6.11 1) To calculate interactions between neutral species (atoms or molecules) you can use the Lennard-Jones equation. Suppose two He atoms interact according to the Lennard Jones equation a )Calculate the potential energy of interaction V(r) if the two He atoms are separated by 2.50x10 -10 m. From the sign of this value for V(r), is the interaction repulsive or attractive? Assume the well depth and Answer: V(r)= 9.94 x 10 -26 J. Because r< σ , V(r)>0 so the interaction is repulsive. b) Repeat the calculation for r=3.50x10 -10 m. Is the interaction attractive or repulsive at this distance? Answer: V(r)= -7.31x10 -26 J. V(r)<0 so interaction is attractive. 2) To calculate interactions between ions in free space (i.e. NOT in solution) you can use

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Unformatted text preview: the expression where n 1,2 is the positive or negative integer charge of the ion, e.g. for Na + interacting with Cl-, n 1 =+1 and n 2 =-1. To do these calculations you need the free space permittivity constant and the unit charge . a) Using your values for and e, calculate . Solution: b) Calculate the Coulombic interaction V(r) between two Ca 2+ ions separated by r=2x10-9 m. Solution: c) Calculate the interaction per mole of Ca 2+ pairs Solution: 3) Using the Table of bond enthalpies provided, calculate the reaction enthalpy for: Note : O 2 is O=O and CO 2 is O=C=O. Bond C-H C-O O=O O-H C=O Enthalpy (kJmol-1 ) 413 358 495 467 799 Solution: Calculate total enthalpy of bonds broken: Now calculate the enthalpy of bonds formed: Final calculation:...
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