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Science Student

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Meson (3/13)



  1. There is something deeply wrong with how I am trying to understand this. I know that the surface of the water exposed to the atmosphere doesn't matter because I have read it in multiple sources. But I don't understand why. When I look at the picture that you posted at the top, I see that there is a certain amount of surface area of water in the petri dish that is exposed to atmospheric pressure. So, the equation pressure = force/area leads me to believe that force = area*pressure which seems to mean that the more surface there is the more force will be applied to the water. Or as an example, if I apply x pressure to a 2m^2 side of a rock, then the force applied = 2m^2*x. But if I apply x pressure to a different side of the rock that is 3m^2, the force is greater f = 3m^2*x; this might move the rock where the other force might not. This is driving me crazy because I know I am wrong, but I feel like I am right.
  2. Oh I see. What about the size of the petri dish; do you think that the more surface for the atmosphere to push on, the more water weight that can be held up in the down glass upside down?
  3. I have read what you have in your second paragraph before, but I don't understand it. I understand that the atmospheric pressure acts on the surface of the water in the petri dish. So then why would water come out of an open test tube if the test tube was not submerged in the water of the petri dish? Does it have something to do with the surface of the water that the atmospheric pressure acts on? If so, then wouldn't this "10m rule" require a certain area of water that the atmospheric pressure must act on? The equation that I was hoping for to make sense of all of this would have a water surface variable included.
  4. As a thought experiment, I imagine having a full cup of water sealed with plastic saran wrap. I think that if I turned it upside down in a shallow puddle of water in a petri dish and slipped off the saran wrap, then the water would probably come out of the glass causing the petri dish to overflow. So how much water do I need for the atmospheric pressure to be enough to keep the water in the glass.
  5. But then why does the pressure change and not the temperature? Or why doesn't pressure and temperature change?
  6. Damn, I did not explain the issue properly. I should have asked how temperature can be a function of volume. In other words, how does decreasing the volume of a container increase the temperature of the gas? Or would it? In terms of V1/T1 = V2/T2, I don't think my air compressor heated up when it would take in and compress the air. Although I may not have noticed.
  7. I understand how pressure is a function of temperature, but not how temperature a function of pressure. My notes have: initial volume / initial temperature = final volume / final temperature. This seems to mean that adding pressure increases temperature. But how does pressure increase the average kinetic energy of the air molecules? I can understand how increasing the average kinetic energy of air molecules increases the pressure on the walls of the container. But vice versa doesn't make sense to me.
  8. Thank-you, and thank-you for giving your opinion about the link; that is helpful too.
  9. Thanks for your help, but it's just that my textbook doesn't seem to get into enough details for this question. I found an answer that seems correct at http://www.chemguide.co.uk/atoms/bonding/hbond.html about a third of the way down.
  10. Knowing the number of hydrogen bonds for these polar molecules is not something that is covered in the material before the question. However, I see that there would probably be more hydrogen bonds in HF per molecule than H2O because there are more lone pairs on F for hydrogen from the other hydrogen fluorides to bond to. This makes HF's boiling point even more counterintuitive to me.
  11. HF has 3 lone pairs and H2O has 2 lone pairs. H2O is a bent tetrahedral, and HF has only a single bond, so I am not sure what to call it. This question is in my textbook for grade 11 chemistry; it wants me to know why, but I can't find anything in the chapter that explains it.
  12. I checked the electronegativities of the intermolecular forces, and the difference between fluorine and hydrogen is 1.8, much higher than oxygen and hydrogen which is 1.2. So there must be another reason other than hydrogen bonding why H2O has such a higher boiling point than HF, which is only 19.5c. Also, why isn't HF called hydrogen monoflouride?
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