Journal 9/29/15 Try to describe as best as you can what’s happening to water when you boil it. Objective Tonight’s Homework To learn how pressure deals with boiling temperature none

Notes on Boiling and Pressure So what happens to water molecules when you boil water? We know water turns from a liquid to a gas, but what’s actually going on?

Notes on Boiling and Pressure So what happens to water molecules when you boil water? We know water turns from a liquid to a gas, but what’s actually going on? All molecules move. Water molecules bounce around and hit each other all the time. Some of them even try to bounce up and out of the water. This is what you see when steam is rising off something. Water molecules escaping and going into the air.

Notes on Boiling and Pressure So why don’t we see all water steam all the time? 2 reasons: 1) Most of the water molecules don’t have enough energy to jump out into the air. 2) The air is made of molecules, too. These ones move faster and push water molecules back down!

Notes on Boiling and Pressure The higher you go from sea level, the thinner the air gets, and the more the water molecules can push back and escape. This is why water boils at 212° F at sea level, but only 203° F here in Colorado.

Notes on Boiling and Pressure This is where things get interesting. If we want water to boil, we can either heat it up until the water molecules have more energy than the air. OR We can lower the air pressure until the water is pushing up harder than the air is pushing down. With a low enough pressure, we can make cold water boil!

Notes on Boiling and Pressure The idea of cold water boiling is strange, but we can make it even weirder. If we can boil cold water, what about boiling freezing water? Can we make ice boil straight to steam? Yes! This is a process called “sublimation”. We can also turn steam straight to ice. This is called “deposition”.

Notes on Boiling and Pressure We can put all of this together into one graph. We make the graph have temperature on the bottom and pressure on the side. We call this graph a “Triple Point” Diagram.

Notes on Boiling and Pressure We can put all of this together into one graph. We make the graph have temperature on the bottom and pressure on the side. We call this graph a “Phase Diagram”. If we look closely, we have one special point where all 3 phases of water can happen at once. This is called the “Triple Point”. For water, this happens at 0 °C and a pressure of ATM (air only 0.6% as thick as what we breathe)

Notes on Boiling and Pressure Every substance out there has a phase diagram and a spot where it can be solid, liquid, and gas at the same time. Weird but true!

Videos on Boiling and Pressure This stuff is pretty cool visually, so let’s watch a few videos.

Exit Question What happens at a triple point? a) The amount of stuff we have triples b) All solids turn to liquids, all liquids turn to gas, all gasses turn solid c) A substance can be solid, liquid, and gas all at once d) A substance stops existing e) There is no such thing as a “triple point” f) Who knows. No one has ever done it.