00:03
Hi there.
00:04
To answer this question, we need to define what boiling point is.
00:10
So the boiling point of a substance is defined as the temperature at which the vapor pressure of the liquid equals the atmospheric pressure.
00:50
Okay, so we need to make these two equal for a solution or for a liquid to boil.
00:56
So we want the vapor pressure to equal the atmospheric pressure.
01:03
And there are actually two ways to achieve this.
01:07
We could heat the liquid to increase the vapor pressure, or we could decrease the atmospheric pressure until the two are equal.
01:27
So this explains why in the mountains water boils at a lower temperature, because when you're up in the mountains, there is lower atmospheric pressure.
01:37
So you don't have to heat the water to as high of a temperature for the vapor pressure to equal the atmospheric pressure.
01:43
So water boils in the mountains at a temperature below 100 degrees celsius.
01:49
When we talk about water boiling at 100 degrees celsius, that is the normal boiling point.
01:54
That is the boiling point at one atmosphere of pressure.
01:59
That is not always the boiling point.
02:02
That is just the boiling point when we have exactly one atmosphere of pressure.
02:06
Okay, so let's look for our correct answer here.
02:10
When liquid boils, which is true, the partial pressure of the gas phase molecules is constant.
02:17
No, not really.
02:20
The next one, the vapor pressure of the liquid equals the ambient atmospheric pressure...