***General question***

[m3lowrider]

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Really basic concept that I do understand, but Kaplan and Achiever/Destroyer explain this differently in questions. Kaplan explains that boiling point is the temp at which the vapor pressure exceeds the ambient pressure. Destroyer/achiever says that boiling pt is the temp at which vp and ap are equal. I know bp is when they are both equal but want to know why they are different.

thanks

 

[IdahoDoc]

Because Kaplan is wrong 👍

 

[DoCt0rPeTe]

destroyer is correct. however, you are at the bp if it is greater. so in a sense they are both correct.

but the def of bp is when vp is equal to external pressure.

vp pushes up. ambient p (ap for short) pushes down on the solution. thus, in order to get soln molecules into the gas phase, they must escape from the soln, so the vp must increase to a point that is greater than or equal to the ap in order for boiling to occur. (If the ap is greater, then it will just keep the molecules from escaping). At the exact moment when these pressures are equal, you are said to have reached boiling point. but that doesn't mean that something won't boil if vp is greater than ap.