How to Convert Between Joules and Kilojoules in Quantum Theory

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SUMMARY

The discussion focuses on converting energy values from joules to kilojoules in the context of quantum theory, specifically regarding molecular vibrations with a period of 20 femtoseconds (fs). The relevant equation used is ΔE = h/t, where h is Planck's constant. The participant successfully calculated energy in joules but struggled with the conversion to kilojoules per mole, realizing the need to account for Avogadro's number to convert the energy per molecule to energy per mole. The correct conversion involves recognizing that 1 kJ equals 1000 J and applying this alongside Avogadro's number.

PREREQUISITES
  • Understanding of quantum mechanics concepts, particularly molecular vibrations.
  • Familiarity with Planck's constant (h) and its application in energy calculations.
  • Knowledge of unit conversions, specifically between joules and kilojoules.
  • Awareness of Avogadro's number for mole calculations.
NEXT STEPS
  • Study the application of Planck's constant in quantum energy calculations.
  • Learn about Avogadro's number and its significance in chemistry.
  • Research detailed methods for unit conversion in physical chemistry.
  • Explore molecular vibration theory and its implications in quantum mechanics.
USEFUL FOR

Students in chemistry or physics, particularly those studying quantum mechanics and energy calculations, as well as educators looking to clarify concepts related to molecular vibrations and energy conversions.

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Homework Statement



Calculate the size of the quantum involved in the excitation of a molecular vibration of period 20 fs. Express the results in joules and kilojoules per mole.

Homework Equations



ΔE = h/t

The Attempt at a Solution


I converted fs to seconds and used the above equation to figure out the answer in terms of joules, no problem. I have checked my answer for this, so I know it is correct. I also know what the answer is in terms of kilojoules per mole, but I can't for the life of me figure out exactly how to convert between the two. It doesn't seem as though I'm given enough information in the problem to do this conversion. I assumed that I would need to use the fact that 1000J=1kJ, but that doesn't seem to match up with the answer sheet that I was given.
 
Last edited:
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You know energy required to excite one molecule. How many molecules in a mole?
 
That was so simple! Thanks!
 

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