## Photon336 one year ago Question

1. Photon336

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2. Photon336

@Rushwr

3. Photon336

223. Vapor pressure and temperature are proportional b/c when you raise the temperature the fraction of molecules that can escape into the gaseous phases increases and therefore the vapor-presure goes rises. Hydrogen bonding, this would affect vapor pressure because it is a property that depends on Intermolecular forces. the presence of hydrogen bonding between molecules would require more energy to break those bonds and allow those molecules to get into the gaseous phase. (i'm guessing that this would lower the vapor pressure). The presence of solutes is a colliagitive property, one that depends on the number of molecules one dissolves into a solvent, rather than their identity. adding a solute would technically raise the boiling point because it would just take longer for those molecules to go from (l)-->(g). I think it would affect vapor pressure. External pressure: the vapor pressure continues to rise until it equals the external pressure, and boiling occurs. although the external pressure will dictate when a substance will boil, it does not have a direct effect on the vapor pressure in my opinion. I believe that the answer is External pressure

4. Photon336

@Bozhena thoughts on 221?

5. anonymous

I try to figure out which between A and D

6. anonymous

222. is D, Cus Carbonates, Phosphates,sulfides are insoluble

7. Photon336

224. This question relates to a gases solubility in water.. @rushwr thoughts? not sure..about gas suability in liquids? $HCl _{g} + H _{2}O(l) ---> H _{3}O ^{+} + Cl-$

8. Photon336

224. To me why would HCL exist primarily as molecules? it would most likely be H+ + Cl- to me A was false. B I believe that this is that answer because you've have in situ all the gas dissolved and reacted already so you would also have Cl- ions in your solution. C. from the formula I wrote above hydronium ion concentration would go up. Cl- does not raise the pH i think it's B.

9. Photon336

@Bozhena you were right 222. D 223. A 224. B

10. Photon336

how do we figure out whether a gas is soluble in a solution? (it's like dissolves like right?)

11. anonymous

The dissolving of a gas in water depends on the interaction between the molecules of the gas and the water molecules. As water is polar and HCl too they will interact with eachother

12. Photon336

Ah I see, the last question we have is 221, I will post some more for us to discuss

13. anonymous

221. D.

14. Rushwr

I'm sorry i couldn't join the convo sum problem with my internet connection @Photon336

15. anonymous

Here's a great example of how the external pressure is EXTREMELY important to vapor pressure! https://www.youtube.com/watch?v=pOYgdQp4euc

16. anonymous

that's so cool. But i dont get why it freez

17. Photon336

@Woodward that's a great video, how would you describe this?

18. anonymous

It freezes because of this fine equation: PV=nRT We know the room was kept at a constant temperature, the volume of that glass thing covering it was a constant, but they lowered the pressure! What does that mean? They had to have removed particles, it's the only thing left free in the equation! $P=n*\frac{RT}{V}$ So now what does removing particles do? Well now there's no longer anything for molecules in the water to hit up against, there's no more atmosphere! |dw:1438540793060:dw| The water molecules are now free to escape, there's no longer a counteracting external pressure. You gotta realize that water molecules are basically weightless on their own, so once they leave they leave into the air and the get sucked out with the pump allowing more to keep bouncing out. But what's left? Just the slow moving water molecules. So really most of the heat left with the ones that bounced out. Keep in mind that they froze into a solid but they're still about 273 Kelvin above absolute zero, so they're still warm in some sense!

19. anonymous

Anyways when you said you thought the answer was A, I knew it couldn't be further from the truth and had to show you something so you couldn't forget haha :P

20. anonymous

Here's another good video I just found of it if you're still curious, I don't want to distract you too much from studying haha: https://www.youtube.com/watch?v=I5mkf066p-U

21. sweetburger

What did you guys come up with as the answer for 223

22. sweetburger

Did you guys choose A? or did you come to another answer choice.

23. Photon336

@sweetburger I chose A, but @Woodward gave a better interpretation so I'm reading that now

24. sweetburger

My textbook states that vapor pressure is independent of atmospheric pressure.

25. Photon336

26. sweetburger

atmospheric/external pressure...

27. sweetburger

For 221 i do not think the answer could be either b or c due to the common ion effect

28. Photon336

the example woodward gives (to my knowledge) demonstrates the opposite.. like if you lower the external pressure seems to have an effect

29. sweetburger

Thats in a vacuum isnt it?

30. Photon336

yeah

31. sweetburger

yeah...

32. sweetburger

Were not looking to completely remove the atmosphere were saying if the atmospheric pressure were to change to increase/decrease would it have an effect on the vapor pressure of the liquid.

33. Photon336

like if i boiled water on top of a mountain, vs at sea level, the BP would be different.

34. sweetburger

Yea same idea as you.

35. Photon336

yeah.. guys how do i QUOTE someone?

36. sweetburger

What I meant to say is that it is easier to boil water on the top of a mountain than it is to boil water at sea level. *sorry previous post had a typo

37. anonymous

Right right, I am confusing the stuff, vapor pressure is not affected by external pressure. The reason it boils is because the vapor pressure doesn't depend on external pressure. It was always the same, it's just the external pressure it was pushing against has been removed. The answer is definitely A. Haha sorry for the confusion.

38. sweetburger

Yes, perfectly explained.

39. Photon336

I always thought that boiling occurred when they vapor pressure = external pressure, you mentioned that the external pressure was removed? once that happens.

40. Photon336

so.. the external pressure has been overcome once boiling has occurred?

41. anonymous

Exactly. So you could either give the liquid enough energy so that the molecules are moving fast enough that they can "jump off" into the air or you can remove some of the air and there's nothing holding them in anymore

42. anonymous

|dw:1438542280001:dw|

43. sweetburger

So at the top of the mountain it just takes less water molecules to escape the surface to cause the liquid to boil.

44. anonymous

It takes less heat, not less water molecules. So one molecule of water takes less energy to leave the cup of water into the air while on a mountain but if you were down lower where the pressure is higher, then it takes more heat to make that same molecule escape the rest of the water.

45. Photon336

Pressure goes down so, lower temp = less energy

46. Photon336

maybe I over simplified that

47. anonymous

Heat is Energy @sweetburger Yeah @Photon336 I don't know, since lower temp = less energy is always true because temperature is average kinetic energy of the particles, saying lower temperature means lower average kinetic energy.

48. sweetburger

@Woodward wasnt disputing that

49. anonymous

Yeah I was just trying to clarify cause I sorta just said "energy" and "heat" separately but I didn't want to confuse you haha

50. Photon336

energy/heat not necessarily the same, i believed i confused that with temperature

51. sweetburger

I was saying it takes less water molecules to reach the same atmospheric pressure and I was inferring that it is known that it takes heat for the water molecules to escape the surface of the liquid.

52. sweetburger

In regards to this post "So at the top of the mountain it just takes less water molecules to escape the surface to cause the liquid to boil. "

53. Photon336

okay.. that makes sense

54. Photon336

@Woodward the first video you showed. was the pressure decreased or increased? trying to look at the graph @Bozhena posted

55. anonymous

P decreased

56. Photon336

started off with liquid water, at constant volume, I see the pressure must have deceased to get it to solid ice eventually

57. Photon336

but in the first part it evaporated went from liquid to gas so under those conditions i'm assume you would have to increase the pressure to do that?

58. Photon336

Just trying to make sense of this and connect it to the phase diagram for water.

59. anonymous

I don't know if this graph completely explains the video, because this graph is from equilibrium thermodynamics but here we had an open system (we were removing particles from the system with the vacuum) so that's how we were able to maintain constant temperature and freeze it at room temperature. |dw:1438543223019:dw| See that's the line of constant temperature we travelled down

60. anonymous

Wait.... I don't think what I put is right hahaha Oh well I'll leave it up maybe we can find the error

61. Photon336

Well you decreased the the pressure at a low temperature (assuming under conditions of constant volume)

62. Photon336

no wait

63. Photon336

shouldn't the pressures be reversed?

64. Photon336

we started off with liquid so we would have had to increase the pressure under those conditions..

65. anonymous

Oh she flipped liquid with gas that's all: http://christophercapp.com/wp-content/uploads/2013/09/Triple-Point-Diagram-011.jpg

66. anonymous

My mistake, it too confusing, the diagram do not explain the phenomenon. So the best explenation is @Woodward. As the molecure had no more pressure they are free to go away. But to turn in to the gas they need to use they own evergy, so after some time than they boiling they loose a lot of Kinetic Energy and freez.

67. anonymous

|dw:1438543545122:dw| All good we're all confused here this is kinda fun figuring this out together @Bozhena @Photon336 @sweetburger

68. Photon336

yes haha

69. Photon336

Guys I will post another one and close this out soon

70. Photon336

last thing so this graph can't explain the phenomena for the vacuum totally because this is for an open system?

71. anonymous

nice ;) Sorry for the mess

72. anonymous

no, cuz it do not consider the lost of energy, in out case lost of kinetic energy.

73. Photon336

That's good to know

74. Photon336

yeah cuz we kept temperature constant

75. Photon336

Will post another question =D