Molecular Vibrations: Mechanism, Energy Source & More

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Discussion Overview

The discussion revolves around the mechanisms of molecular vibrations, the sources and destinations of energy associated with these vibrations, and the relationship between molecular behavior and temperature/pressure. It explores theoretical concepts, quantum mechanics implications, and the nature of thermal energy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that molecular vibrations are driven by coulomb forces and can be understood through the concept of a quantum oscillator.
  • One participant suggests that the energy associated with molecular vibrations is intrinsic and does not change, while also noting that energy can be stored in electrons occupying different orbitals.
  • It is mentioned that molecules can exchange energy with their surroundings through collisions or interactions with radiation.
  • There is a discussion about whether the frequency of molecular vibrations is dependent on temperature and pressure, with some suggesting that it is independent of surroundings but that the dominant frequencies depend on molecular energy, which is temperature-dependent.
  • Another participant introduces the Heisenberg Uncertainty Principle to explain why molecules cannot remain still, asserting that this leads to the concept of zero-point energy.
  • One participant critiques the relevance of the zero-point energy explanation, arguing it does not adequately address the nature of thermal energy.
  • There is uncertainty about the original question's intent, with some suggesting it may relate to zero-point energy while others believe it could be broader.
  • A later reply attempts to clarify the distinction between intrinsic vibrational energy, bond energy related to temperature/pressure, and zero-point energy, questioning the accuracy of these distinctions.

Areas of Agreement / Disagreement

Participants express differing views on the nature of molecular vibrations and the relevance of zero-point energy, indicating that multiple competing interpretations exist. The discussion remains unresolved regarding the clarity of the original question and the implications of thermal energy.

Contextual Notes

Some participants note that the original question may not be clearly defined, leading to varied interpretations of the concepts discussed. There are also references to complex relationships between energy types and molecular behavior that remain unexplored.

nuby
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I've heard molecules are constantly moving or vibrating. What is the mechanism behind this? Where does the energy come from, and go? Is it always a function of temperature/pressure?
 
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nuby said:
What is the mechanism behind this?

Generally speaking these oscillations are driven by coulomb forces. For more details you may want to read about quantum oscillator.

Where does the energy come from, and go?

Molecule that is excited just 'has' its energy, and its energy doesn't change. You may say that this energy is stored in vibrations.

Edit: it is a little bit more complicated, as the energy can be also stored in electrons occupying different orbitals, let's assume that electrons are not moving fom one orbital to another for now. Besides, to excite electron we usually need much more energy than to exctite bond vibrations.

Molecule can exchange energy with surroundings through collisions or interacting with radiation.

Is it always a function of temperature/pressure?

For a given molecule (to some extent for a given bond) frequency of the possible vibrations is independent on the surroundings. however, which frequencies dominate depends on the molecule energy, which in turn is a function of the temperature.
 
It may be useful to consider why molecules can't stay still. This phenomena is somewhat tricky to understand because it arises fully from quantum mechanics.

First, consider the Heisenberg Uncertainty Principle. This principle states that we cannot know the exact momentum and position of a particle simultaneously. If we know the exact position of a particle at a certain time, then we cannot know its precise momentum (i.e. speed and direction) and vice versa.

So, consider an unmoving particle. Since it is not moving, we know that it's momentum must be zero. Furthermore, because it is not moving, we would also know it's precise location. Therefore, an unmoving particle violates the Heisenberg Uncertainty principle and cannot exist even at absolute zero. This requirement for particles to have momentum (and therefore kinetic energy) at absolute zero is what is known as the infamous zero point energy.
 
Ygggdrasil: No offense, but that's a pretty useless answer.
It explains why molecules aren't still at Absolute Zero, which is an unattainable temperature. It doesn't really explain the why-and-hows of thermal energy in general.
 
Nah, Ygg can be right - it is 100% not clear what the OP asks about. Could be the original question is about the zero point energy. Could be it is not.
 
Ok, so here's my understanding now. Molecules just have an intrinsic vibrational energy that can be considered stored energy.. This energy can't be utilized, and is just "there"... It has no special name.

Then there is a bond energy "vibrational", (separate from above) that is a function of pressure/temperature.

Then a molecules zero-point-energy only exists when the molecules are at 0K ... Above 0K zero-point energy doesn't exist (or not measurable?)

Is this accurate?
 
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