Perfect gasses temperature vs kinetic energy per molecule

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SUMMARY

The discussion focuses on the relationship between temperature and kinetic energy in perfect gases, specifically through the ideal gas law, PV = RnT. It is established that the average kinetic energy (KE) per molecule is given by the formula KE = (3/2) * (PV/n), which accounts for translational motion. Additionally, the discussion highlights that the traditional expression for kinetic energy is KE = (3/2) * N * k * T, where k is Boltzmann's constant (1.38E-23 J/K). This indicates that kinetic energy is directly proportional to temperature, with three modes of motion contributing to the overall energy.

PREREQUISITES
  • Understanding of the ideal gas law (PV = RnT)
  • Basic knowledge of kinetic energy concepts
  • Familiarity with Boltzmann's constant (k = 1.38E-23 J/K)
  • Concept of translational motion in physics
NEXT STEPS
  • Study the derivation of the ideal gas law and its applications
  • Learn about the different modes of molecular motion (translational, rotational, vibrational)
  • Explore the implications of Boltzmann's constant in thermodynamics
  • Investigate the relationship between temperature and energy in various states of matter
USEFUL FOR

This discussion is beneficial for students studying physical chemistry, physics enthusiasts, and anyone seeking to understand the fundamental principles of thermodynamics and kinetic theory in gases.

madah12
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Homework Statement


I have been wondering about temperature and it's relation to kinetic energy I didn't study thermodynamics so I hope that replies could be simplified.I am trying to think about the perfect gas law to relate kinetic energy per molecule to temperature, and I want to know if I have a somewhat close understanding.


Homework Equations


PV=RnT


The Attempt at a Solution


PV=RnT
I am thinking that P*V expresses the energy stored in the gas molecules since P =F/A and V=m^3 so P*V=F*m which is the unit of work so W=RnT
and since the work expresses the change of kinetic energy
deltaK= RnT
(delta K)/n = RT
so this gives me the intuition that since the change of kinetic energy per molecule is equal to a constant times the temperature so its proportional to it. I didn't study thermodynamics and only basics of physical chemistry so probably there are things I missed but is my intuition at least correct?
 
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Your intuition (or subconsciously-remembered info) is in the right direction
... but the PV is related to the Work that can be done on the Area (2-d),
not the entire molecule KE , which comes from motion in all 3 dimensions.
So, the KE per molecule (an average, of course) is actually 3/2 * PV/n .
... this is translational KE of the molecule's center-of-mass, not including
rotational KE and vibrational KE of the atoms relative to that c.o.m.

It is more traditional to write KE = 3/2 N kT , with N being the number of molecules,
and k is Boltzmann's konstant = 1.38E-23 J/K , which is R/N_avagadro .
The "3" signifies that there are 3 modes of motion which contribute to this KE ; every mode (including means rotations and vibrations also, if they occur) in a molecule holds E(average) = 1/2 kT .
 

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