Electrostatic energy of two opposite charges in water and in a vacuum

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SUMMARY

The discussion focuses on calculating the electrostatic energy of two opposite charges, e and -e, separated by 7 angstroms in both water and a vacuum. The relevant equations are E = -\frac{e^2}{4\pi \varepsilon D r^2} for electrostatic energy and the Bjerrum length, λ_B = \frac{e^2}{4\pi \varepsilon k_B T}. The dielectric constant (D) is 80 for water and 1 for vacuum, confirming that the Bjerrum length is not the distance between the charges but a measure of interaction strength in a medium. The final energy expressions incorporate these constants and the distance between charges.

PREREQUISITES
  • Understanding of electrostatics and Coulomb's law
  • Familiarity with dielectric constants and their significance
  • Knowledge of Bjerrum length and its application in electrostatics
  • Basic principles of thermodynamics, particularly k_B and T
NEXT STEPS
  • Explore the derivation and implications of Bjerrum length in different solvents
  • Study the effects of temperature on electrostatic interactions in various media
  • Learn about the role of dielectric constants in electrostatic energy calculations
  • Investigate the applications of electrostatic energy in biological systems
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Students and researchers in physics and chemistry, particularly those studying electrostatics, molecular interactions, and thermodynamic properties of solutions.

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Homework Statement



Compare the electrostatic energy of two opposite charges e and -e, a distance 7 angstroms apart in water at room temperature and that in vacuum (express the energy in terms of Bjerrum length)

Homework Equations



E = 1/(4(p\pi\epsilonD)*(-e^2)/r^2 ?

The Attempt at a Solution



First of all is this the right equation to use? If so, is the Bjerrum length the distance between the charges? And for a vacuum is the dialectic constant (D) just 1?
 
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Electrostatic energy is:E=-\frac{e^2}{4\pi \varepsilon D}
Bjerrum length:
\lambda_B=\frac{e^2}{4\pi \varepsilon k_BT}
 
So, for water:
E=\lambdaKT/80?

And for a vacuum:
\lambdaKT?
 
No, we have:
\lambda_B k_BT=\frac{e^2}{4\pi\varepsilon}
so put it into formula for energy
 
I did do that, D=80 for water and D=1 for a vacuum
 
In my formula "D" denotes distance
 
Ok that makes sense, so D is dialectric constant and let's say r now is the distance, which is missing in the equations.
 

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