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treddie
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What does it mean to heat an isolated atom with photons, from a hypothetical 0deg, to 100deg? What is happening in the atom's electron shells, and how long can the atom retain the heat?
The total energy of a molecule is potential energy (excited state) plus kinetic energy E (heat) (mv2/2). Put your hand in a hot oven and feel convection of heat (kinetic energy) in air. The momentum of gas molecules (=sqrt(2mE)) hitting walls of enclosures is what creates gas pressure.treddie said:Well, pretty much the only way a single isolated atom can gain energy is to absorb a photon, which increases the principal quantum number of one of its electrons. But the electron would almost immediately drop back down to the ground state (that's a probabilistic process, but the lifetime is very short). And besides, that doesn't really count as "heat." If you're really going to heat an atom up, it needs to be in some sort of potential that allows it to vibrate, or at least move around without leaving a confined area..
You are correct that the mean velocity is zero. If there are a billion atoms moving to the right, and a billion to the left, the average velocity is near zero. But the sum of the squares of the velocities of all molecules is a positive definite number, as is the average of the squares of all velocities. So the square root of the average is also positive definite. At low temperatures, nearly all the "heat" energy in gas molecules is kinetic energy. My equation above is just an extension of the ideal gas equation PV = nRT, covered in most high school and college freshmen physics books.treddie said:The equation "(1/2)Mv2 = (3/2)RT" seems confusing to me since I can't imagine that the overall velocity of a heated atom would be anything other than mean zero. We know that photons transfer momentum to atoms, but unless all of the photons are coming from a given direction, their directions of collision with the atom are random and should sum to mean zero. And when the atom is NOT in isolation, velocity would at least in part, depend on pressure, which is absent from the equation.
gonegahgah said:If you have two isolated photons that are traveling separate paths which during their journey come close enough to "freeze" together will heat radiation be released?
gonegahgah said:Oops! I meant atoms
mikelepore said:treddie, if I read you right, I think you said you expect a low temperature when the density is very low? That doesn't follow. The average kinetic energy of a group of particles doesn't become small just because there are few particles. Compare to other examples of averages -- the average speed of ten cars isn't necessarily smaller than the average speed of a thousand cars.
To refer to "the heat in" individual substances or locations is an incorrect use of the word. Things have internal energy. The word heat only refers to the transfer of energy from one body to another, for example, the conduction of heat from a higher temperature region to a lower temperature region.
Heat is a form of energy that is transferred from one object to another due to a difference in temperature. It affects isolated atoms by causing them to vibrate and move faster, which can change their physical and chemical properties.
Photons are particles of light that carry energy. They interact with isolated atoms by transferring their energy to the atoms, causing them to become excited and potentially change states.
Both heat and photons contribute to the overall energy of isolated atoms by providing them with energy to vibrate and move, as well as potentially causing them to change states and release energy.
High heat or intense photon exposure can cause isolated atoms to become highly excited and potentially ionized, meaning they lose or gain electrons. This can lead to changes in the atom's chemical properties and behavior.
Understanding the effects of heat and photons on isolated atoms is crucial in various fields such as materials science, chemistry, and engineering. It allows scientists to manipulate and control the properties of atoms, leading to advancements in technology and the development of new materials with unique properties.