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Boiling Point - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Boiling point is the particular temperature where vapor pressure equals to of a liquid equals to the surrounding environmental liquid. At this temperature the liquid begins to bubble as liquid below the surface turns to gas and escapes upwards.

Alright, so we're going to talk about boiling point and boiling boiling point is the, is the time and place where the liquid state of the substance goes into a gaseous state of that substance. We're going to call that, the time when it does that the boiling point. Alright. That happens when the vapor pressure equals the atmospheric pressure. So vapor pressure of the substance equals the atmospheric pressure of the atmosphere around it.

Let's take this beaker of water as an example. Okay, so at the surface of this water, at the surface of this liquid water, the water molecules are constantly going back and forth. It's from the liquid phase to the gaseous phase. Back and forth, back and forth. And if I increase the temperature, that vapor pressure is going to continously increase. The vapor pressure meaning the pressure of the water molecules going into the atmospheric pressure, to the atmosphere around it, sorry. So that continuously to the point where this vapor pressure equals the atmospheric pressure around it, we're going to call that boiling and what's going to happen at that point, not only are these surface water molecules going to get into the atmosphere but these guys down here are going to be released into the atmosphere as well which is what causes that rolling boil or that the bubbles from the bottom is the gaseous water molecules going and releasing from the liquid substance.

So the definition when vapor pressure equals atmospheric pressure, we're going to talk about the boiling point in different areas on earth Okay, so at sea level, where we typically are, where I live in DC, I live at sea level. So the atmospheric pressure or the pressure air pressure around me is one atmosphere. Okay? The boiling point at one atmospheric pressure is 100 degrees celsius. Okay?

So let's say I were to leave DC and go on to climb mount Everest. If I'm climbing up the top of mount of mount Everest, that's me with my American flag, and that happens the atmosphere is actually the the atmospheric pressure decreases meaning the number of air particles on top of me is actually less than they were at sea level. What's going to happen to the boiling point? Because, vapor pressure has to equal atmospheric pressure. The atmospheric pressure lowers. That means the vapor pressure doesn't have to go up as high, it means the boiling point is also going to lower. Okay?

Actually, in Denver, often known as mile high city, the boiling point of water is not 100 degrees celsius. It's 95 degrees celsius. And actually on top of mount Everest, it's even more drastic. The boiling point of water there is only 69 degrees celsius, you can believe that because it's so so so high and the atmospheric pressure is so so so low.

Alright, let's do the opposite. Let's maybe go down to the lowest point on the planet, which is the Dead Sea. The atmospheric pressure there is extremely high meaning there's a lot of air molecules pouring down on top of us. It's very high pressured down there. The boiling point too, also would be much higher because it's going to take a lot of energy for us to reach that atmospheric pressure for that vapor pressure of the water to reach the atmospheric pressure surrounding us. So the near the Dead Sea the boiling point is much much higher. It's around 176 degrees celsius, extremely high.

So let's think about how this may play effect in other areas. I'm going to talk about, let's say pressure cookers. If some of you guys have parents have pressure cookers at home, typically or these rice cookers, what happens in these cookers is that we increase the pressure within that cooker, okay? If we're increasing the pressure the boiling point is actually increasing so that water can get very very hot within that rice cooker or pressure cooker. So you can actually cook things at very high temperatures which is why they're so good and convenient to use when we're cooking.

So that's how pressure affects the boiling point of different substances.