'Experiments' – Evaporation, boiling and Bubbles

‘Experiments’ – Evaporation, boiling and Bubbles. A video produced at Manchester Metropolitan University.
Video from SciTutors website.


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6 thought on “'Experiments' – Evaporation, boiling and Bubbles”

  1. 1. Petrol/gasoline has a high vapor pressure. Water's vapor pressure ranges from less than .1 to 14.7 psi from 32 to 212 degrees F. In contrast, gasoline is roughly 51 to more than 257 psi. Gasoline is straining to get free of its liquid prison. As long as there is some vapor pressure, some evaporation is happening. If vapor pressure exceeds atmospheric/surrounding pressure (14.7 psi, so gasoline's does), the substance will actually just boil, which is much quicker than just evaporation. Not sure if it's evaporation + boiling or just boiling for the gasoline but it's due to the vapor pressure anyway.
    2. Evaporation (& boiling), which is already fast in gasoline, will speed up considerably with more surface area and mixing (more opportunity for higher-energy gasoline to escape into its gaseous form). Just like sweating cools you down more when you are moving fast or someplace windy, quick evaporation/boiling of gasoline will cool the water at the bottom of the beaker down much more quickly. In addition, the water itself releases its high-energy particles through evaporation at the same time. It stands to reason that in this case very cool gasoline and cooled-off water combined can even have lost enough energy to bypass the freezing point energy barrier of water. You'd expect the same scenario without the pump to produce merely cold (say 40-degree F) water on the bottom of the beaker.
    3. Hot water (past 50 degrees F) is at most 4% lighter than cold water, so it floats to the top. Hot water has lower viscosity (about five times lower) than cold water, so it is more prone to moving around and creating bubbles as well as migrating to its proper position based on how heavy it is. The mist confuses me.
    4. Taking air out means reducing pressure to zero. Water no longer under pressure means its vapor pressure has effectively increased (p_v,effective = p_v,water – p_on.water). Normally the pressure on water is atmospheric pressure (14.7 psi). Thus, as we saw in experiment 1, the substance with effectively lower vapor pressure evaporates more readily. And when the effective vapor pressure is less than its surroundings, well, that is again the condition for boiling, due to the liquid's chance of changing to the gaseous state.
    5. Same as 4.
    6. Shaking produces bubbles/more surface area, and more pressure from the vapor produced. To return to equilibrium, once there's no barrier to it in the form of a seal on the can of pop, air / CO2 / pop will be forced out (reducing the pressure due to less stuff bouncing around). As for why it's foamy, well, the CO2 dissolved in the pop allows that shape to hold I believe. If this experiment was done with water instead, to get a similar effect you'd have to heat up one can and shake it up. You may get some foam but not too much unless the water is full of some other junk (not pure distilled). It'd just be a stream of water/steam/that sound I think.

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