5 ms·

For me it was this line: > In the natural world, evaporation occurs when sunlight warms the surface of the Earth, breaking the bonds which hold water molecules

For me it was this line: > In the natural world, evaporation occurs when sunlight warms the surface of the Earth, breaking the bonds which hold water molecules together. Which is... sort of not inaccurate, but feels like it implies a misleading concept, and makes me think the author copied it without understanding it.

thaumasiotes 3y ago
> Which is... sort of not inaccurate Really? Do puddles not dry up at night? My impression was that evaporation occurs because that's just the way liquid behaves. It's more important that water molecules are really small than that they experience sunlight. Temperature-based evaporation is "boiling", and sunlight doesn't make a meaningful difference there, as far as water goes...?
- Turing_Machine 3y ago
  The phrase "breaking the bonds which hold water molecules together" can be interpreted two different ways. 1) Breaking the covalent bonds that hold individual water molecules together, preventing them from splitting into two hydrogen and one oxygen atom. That's clearly not true. 2) Breaking the hydrogen bonds that stick one water molecule to another, keeping the water in liquid form. That's true. In any case, it's poorly phrased.
  - thaumasiotes 3y ago
    Is that right? Molecules with no polarity can still form liquids. It happens all the time; we call those liquids "hydrophobic" (or, most commonly, we call them "oils"). The hydrogen bonds aren't what's keeping the water in liquid form. Cooking oil, notably, will not evaporate the way water will -- if you spill it somewhere, the oil will mostly just stay wherever you left it until you clean it up -- but my understanding was that this is because oil molecules are huge and heavy while water molecules are tiny.
    - thedanbob 3y ago
      There are a number of forces that allow molecules to form liquids/solids, the hydrogen bond just happens to be the one that acts on water. If my memory serves it's the London force for non-polar molecules.
- IanCal 3y ago
  > Temperature-based evaporation is "boiling" I don't think that's true for naming, but regardless warmer water evaporates quicker. And the statement doesn't say evaporation doesn't occur for other reasons, though the wording feels like it implies it.
- quesera 3y ago
  > because that's just the way liquid behaves That's almost worse than the original! :) Water evaporates because their energy (heat) causes the molecules to bounce around and sometimes escape the cohesive attraction of their friends and into the air. More energy, more evaporation. This works well with small water molecules, less well with larger and heavier liquids.
  - BoiledCabbage 3y ago
    > escape the cohesive attraction of their friends Hmm, could you call this mysterious "cohesive attraction" > the bonds which hold water molecules together. ...? If not, then please do describe this cohesive attraction. I've come to realize some people just like to complain on the internet.
    - quesera 3y ago
      The "bonds which hold water molecules together" are, I think, the covalent bonds holding the Hydrogens to the Oxygen. Evaporation does not break those bonds, it's just the intact molecules energetically escaping the surface tension of the liquid. (Disclaimer: My high school chemistry books have not left their shelves in many years, except when moving.)
      - BoiledCabbage 3y ago
        "Surface tension in water owes to the fact that water molecules attract one another, as each molecule forms a bond with the ones in its vicinity." Surface tension is a bond that binds water mold together similar to how mortar holds bricks together in a wall. Mortar doesn't make the brick solid, but it holds the bricks together. People are reading bond in two different ways. Bond within a molecule vs bond between molecules. 1. https://www.usgs.gov/media/images/surface-tension-forms-a-strong-bond-surface-a-water-body#:~:text=Surface%20tension%20forms%20a%20strong,U.S.%20Geological%20Survey https://www.usgs.gov/media/images/surface-tension-forms-a-st...
        paholg 3y ago
- chlorion 3y ago
  Hair dryers and clothes dryers both operate by adding a bunch of heat to the thing they are trying to dry. I am not a physics expert but that seems to suggest that heat helps speed up evaporation!
bilsbie 3y ago
If the air can hold more water at its temperature it will pick up more water.
thesuperbigfrog 3y ago
It depends on the liquid's vapor pressure (https://en.wikipedia.org/wiki/Vapor_pressure https://en.wikipedia.org/wiki/Vapor_pressure) and temperature relative to the surrounding environment. I am very skeptical how much usable power could be generated using the 'drinking bird' approach. Show me the engine or generator that the drinking bird powers . . .

thaumasiotes 3y ago

> Which is... sort of not inaccurate Really? Do puddles not dry up at night? My impression was that evaporation occurs because that's just the way liquid behaves. It's more important that water molecules are really small than that they experience sunlight. Temperature-based evaporation is "boiling", and sunlight doesn't make a meaningful difference there, as far as water goes...?

Turing_Machine 3y ago
The phrase "breaking the bonds which hold water molecules together" can be interpreted two different ways. 1) Breaking the covalent bonds that hold individual water molecules together, preventing them from splitting into two hydrogen and one oxygen atom. That's clearly not true. 2) Breaking the hydrogen bonds that stick one water molecule to another, keeping the water in liquid form. That's true. In any case, it's poorly phrased.
- thaumasiotes 3y ago
  Is that right? Molecules with no polarity can still form liquids. It happens all the time; we call those liquids "hydrophobic" (or, most commonly, we call them "oils"). The hydrogen bonds aren't what's keeping the water in liquid form. Cooking oil, notably, will not evaporate the way water will -- if you spill it somewhere, the oil will mostly just stay wherever you left it until you clean it up -- but my understanding was that this is because oil molecules are huge and heavy while water molecules are tiny.
  - thedanbob 3y ago
    There are a number of forces that allow molecules to form liquids/solids, the hydrogen bond just happens to be the one that acts on water. If my memory serves it's the London force for non-polar molecules.
IanCal 3y ago
> Temperature-based evaporation is "boiling" I don't think that's true for naming, but regardless warmer water evaporates quicker. And the statement doesn't say evaporation doesn't occur for other reasons, though the wording feels like it implies it.
quesera 3y ago
> because that's just the way liquid behaves That's almost worse than the original! :) Water evaporates because their energy (heat) causes the molecules to bounce around and sometimes escape the cohesive attraction of their friends and into the air. More energy, more evaporation. This works well with small water molecules, less well with larger and heavier liquids.
- BoiledCabbage 3y ago
  > escape the cohesive attraction of their friends Hmm, could you call this mysterious "cohesive attraction" > the bonds which hold water molecules together. ...? If not, then please do describe this cohesive attraction. I've come to realize some people just like to complain on the internet.
  - quesera 3y ago
    The "bonds which hold water molecules together" are, I think, the covalent bonds holding the Hydrogens to the Oxygen. Evaporation does not break those bonds, it's just the intact molecules energetically escaping the surface tension of the liquid. (Disclaimer: My high school chemistry books have not left their shelves in many years, except when moving.)
    - BoiledCabbage 3y ago
      "Surface tension in water owes to the fact that water molecules attract one another, as each molecule forms a bond with the ones in its vicinity." Surface tension is a bond that binds water mold together similar to how mortar holds bricks together in a wall. Mortar doesn't make the brick solid, but it holds the bricks together. People are reading bond in two different ways. Bond within a molecule vs bond between molecules. 1. https://www.usgs.gov/media/images/surface-tension-forms-a-strong-bond-surface-a-water-body#:~:text=Surface%20tension%20forms%20a%20strong,U.S.%20Geological%20Survey https://www.usgs.gov/media/images/surface-tension-forms-a-st...
      - paholg 3y ago
chlorion 3y ago
Hair dryers and clothes dryers both operate by adding a bunch of heat to the thing they are trying to dry. I am not a physics expert but that seems to suggest that heat helps speed up evaporation!

bilsbie 3y ago

If the air can hold more water at its temperature it will pick up more water.

thesuperbigfrog 3y ago

It depends on the liquid's vapor pressure (https://en.wikipedia.org/wiki/Vapor_pressure https://en.wikipedia.org/wiki/Vapor_pressure) and temperature relative to the surrounding environment. I am very skeptical how much usable power could be generated using the 'drinking bird' approach. Show me the engine or generator that the drinking bird powers . . .