Understanding CO2 and Water Phase Diagrams

In this video, we're going to talk about the phase diagrams for CO2 and water. But before we jump into that, there are a few things that we need to talk about. So let's go over phase changes. If you go from a solid to a liquid, what is this phase change called? Going from a solid to a liquid, this is called melting. Think of ice. When ice melts into water, it converts from a solid to a liquid. Now what about the reverse, liquid to solid? So when water turns into ice, it's called freezing. Now what about going from a liquid to a gas? Going from a liquid to a gas is known as vaporization. Now what about gas to a liquid? This is called condensation. Now let's say if you place a cold glass cup in a humid environment, you'll notice that water condenses on the outside of the cup. You'll see like water droplets. That's the water vapor in the air condensing into a liquid. Now what about the conversion from a solid directly into a gas, skipping the liquid phase? This is known as sublimation. A good example of sublimation is dry ice, CO2. If you ever watch a YouTube video on dry ice, if you see solid CO2, notice that it converts directly into a gas. It doesn't liquefy. room temperature or rather at 1 ATM at normal pressure it goes directly from a solid to a gas that's why it's called dry ice now if you think about the other one gas to a solid this is simply the reverse of sublimation this is called deposition that's when the gas goes directly back into the solid form Now let's start with the phase diagram for CO2. So on the x-axis we have the temperature and the pressures on the y-axis. Typically the graph looks something like this. So that's just a rough sketch. So here we have the solid, here is the liquid phase, and here is the gas phase. And here is the standard pressure at 1 atm. The point where the solid, liquid, and gas phases coexist is called the triple point. The line between the solid and liquid phase is known as the melting point line because to go from a solid to a liquid it's melting and going backwards from a liquid to a solid is freezing now the line between the liquid and gas phase is called the boiling point curve going from a liquid to a gas we set its out vaporization and gas to a liquid is a connotation Now, at 1 atm, if you increase the temperature for CO2, notice that it goes directly from a solid to a gas. So, CO2 sublimes. Notice that at 1 atm, the pressure is below the triple point. If the pressure was above the triple point, it would go from a solid to a liquid to a gas. But at standard pressure, it's below the triple point, so that's why CO2 sublimes from a solid to a gas. As the temperature increases. Now, here's a question for you. Which phase has a higher density? The liquid phase of CO2 or the solid phase? Because for some materials, the liquid has a greater density, and for other materials, the solids have a greater density. So how can you tell based on the phase diagram? Well, pick a point. Let's start with the liquid phase. As you increase the pressure, the density of the material increases because you're compacting the atoms together. As you squeeze the liquid into the atom, the density of the material increases. atoms into a tighter space there's more mass per unit volume and so it has a higher density so as we increase the pressure notice that we're gonna go from the liquid to the solid phase so we're gonna freeze the substance and that means that the solid phase is at a higher pressure than the liquid phase so in the case of co2 because the the melting point curve has a positive slope the density solid co2 is greater than that of liquid co2 at higher pressures now there's another point of interest and it's called the critical point the critical point is location where you are beyond the temperature and pressure of that point you can have a supercritical fluid a supercritical fluid is a fluid that has properties of a gas and a liquid. It's not exactly a gas and it's not exactly a liquid but it's in between the two. Like a gas it has a lower density than a liquid but like a liquid it can dissolve certain materials. Like a gas it can effuse through different materials. So it has properties of both. Notice that beyond critical temperature which is this point you can no longer liquefy a gas by increasing the pressure if you increase the pressure the gas will go directly to the supercritical phase it won't go into liquid phase gas can be liquefied when the temperature is below the critical temperature if it's above it you're gonna go straight to the supercritical fluid rather than liquefying the gas at high pressure now let's go over the phase diagram for water So it's a little different for H2O than it is for CO2. For one thing, notice that the melting point line has a negative slope instead of a positive slope. As you move towards the right, the line decreases. Now this is still going to be the solid phase, this is the liquid, and this is the gas. phase and this time the pressure of one ATM is above the triple point so because standard pressure is above the triple point as you increase the temperature for let's say ice ice is going to melt into a liquid and as you continue to increase the temperature the liquid will vaporize into a gas so at a pressure of 1 ATM you can increase the temperature and get all three phases of water now if you decrease the pressure below the triple point when you heat up the solid it will sublime directly into a gas So sublimation can occur when the pressure is below the trouble point. Now let's talk about the density of water. Which phase has a higher density? Ice or liquid water? So if we start at this point, and if we increase the pressure, if we go vertically upwards in the phase diagram, notice that we're going to travel from the solid to the liquid. So that means that the liquid is at a higher pressure, and therefore... is more dense than the solid. So liquid water has a higher density than ice. That's why ice floats on water. Now this is still the critical point. And above this region, or in this region, you have the supercritical fluid again. So the temperature at the critical point is called the critical temperature, which is whatever that value is. And the pressure that corresponds to the critical point is the critical pressure. Now, what is the difference between the boiling point of H2O and the normal boiling point of H2O? The boiling point of water can vary, and it's anywhere along this line. However, the normal boiling point of H2O is the boiling point of H2O. normal boiling point is a specific location on that line. The normal boiling point occurs when the pressure of the atmosphere is 1 atm. So this particular point is the normal boiling point of water. whereas anywhere along this line is called the boiling point curve. Now, the normal melting point occurs at a pressure of 1 atm. So, this is the normal melting point. And this is called the melting point curve. So, if you hear the word normal attached to melting point or boiling point, the pressure has to be 1 atm.

In this video, we're going to talk about the phase diagrams for CO2 and water. But before we jump into that, there are a few things that we need to talk about. So let's go over phase changes.

If you go from a solid to a liquid, what is this phase change called? Going from a solid to a liquid, this is called melting. Think of ice. When ice melts into water, it converts from a solid to a liquid.

Now what about the reverse, liquid to solid? So when water turns into ice, it's called freezing. Now what about going from a liquid to a gas? Going from a liquid to a gas is known as vaporization. Now what about gas to a liquid?

This is called condensation. Now let's say if you place a cold glass cup in a humid environment, you'll notice that water condenses on the outside of the cup. You'll see like water droplets. That's the water vapor in the air condensing into a liquid.

Now what about the conversion from a solid directly into a gas, skipping the liquid phase? This is known as sublimation. A good example of sublimation is dry ice, CO2.

If you ever watch a YouTube video on dry ice, if you see solid CO2, notice that it converts directly into a gas. It doesn't liquefy. room temperature or rather at 1 ATM at normal pressure it goes directly from a solid to a gas that's why it's called dry ice now if you think about the other one gas to a solid this is simply the reverse of sublimation this is called deposition that's when the gas goes directly back into the solid form Now let's start with the phase diagram for CO2. So on the x-axis we have the temperature and the pressures on the y-axis. Typically the graph looks something like this.

So that's just a rough sketch. So here we have the solid, here is the liquid phase, and here is the gas phase. And here is the standard pressure at 1 atm.

The point where the solid, liquid, and gas phases coexist is called the triple point. The line between the solid and liquid phase is known as the melting point line because to go from a solid to a liquid it's melting and going backwards from a liquid to a solid is freezing now the line between the liquid and gas phase is called the boiling point curve going from a liquid to a gas we set its out vaporization and gas to a liquid is a connotation Now, at 1 atm, if you increase the temperature for CO2, notice that it goes directly from a solid to a gas. So, CO2 sublimes. Notice that at 1 atm, the pressure is below the triple point.

If the pressure was above the triple point, it would go from a solid to a liquid to a gas. But at standard pressure, it's below the triple point, so that's why CO2 sublimes from a solid to a gas. As the temperature increases. Now, here's a question for you.

Which phase has a higher density? The liquid phase of CO2 or the solid phase? Because for some materials, the liquid has a greater density, and for other materials, the solids have a greater density. So how can you tell based on the phase diagram?

Well, pick a point. Let's start with the liquid phase. As you increase the pressure, the density of the material increases because you're compacting the atoms together. As you squeeze the liquid into the atom, the density of the material increases. atoms into a tighter space there's more mass per unit volume and so it has a higher density so as we increase the pressure notice that we're gonna go from the liquid to the solid phase so we're gonna freeze the substance and that means that the solid phase is at a higher pressure than the liquid phase so in the case of co2 because the the melting point curve has a positive slope the density solid co2 is greater than that of liquid co2 at higher pressures now there's another point of interest and it's called the critical point the critical point is location where you are beyond the temperature and pressure of that point you can have a supercritical fluid a supercritical fluid is a fluid that has properties of a gas and a liquid.

It's not exactly a gas and it's not exactly a liquid but it's in between the two. Like a gas it has a lower density than a liquid but like a liquid it can dissolve certain materials. Like a gas it can effuse through different materials. So it has properties of both. Notice that beyond critical temperature which is this point you can no longer liquefy a gas by increasing the pressure if you increase the pressure the gas will go directly to the supercritical phase it won't go into liquid phase gas can be liquefied when the temperature is below the critical temperature if it's above it you're gonna go straight to the supercritical fluid rather than liquefying the gas at high pressure now let's go over the phase diagram for water So it's a little different for H2O than it is for CO2.

For one thing, notice that the melting point line has a negative slope instead of a positive slope. As you move towards the right, the line decreases. Now this is still going to be the solid phase, this is the liquid, and this is the gas. phase and this time the pressure of one ATM is above the triple point so because standard pressure is above the triple point as you increase the temperature for let's say ice ice is going to melt into a liquid and as you continue to increase the temperature the liquid will vaporize into a gas so at a pressure of 1 ATM you can increase the temperature and get all three phases of water now if you decrease the pressure below the triple point when you heat up the solid it will sublime directly into a gas So sublimation can occur when the pressure is below the trouble point. Now let's talk about the density of water.

Which phase has a higher density? Ice or liquid water? So if we start at this point, and if we increase the pressure, if we go vertically upwards in the phase diagram, notice that we're going to travel from the solid to the liquid.

So that means that the liquid is at a higher pressure, and therefore... is more dense than the solid. So liquid water has a higher density than ice. That's why ice floats on water.

Now this is still the critical point. And above this region, or in this region, you have the supercritical fluid again. So the temperature at the critical point is called the critical temperature, which is whatever that value is. And the pressure that corresponds to the critical point is the critical pressure. Now, what is the difference between the boiling point of H2O and the normal boiling point of H2O?

The boiling point of water can vary, and it's anywhere along this line. However, the normal boiling point of H2O is the boiling point of H2O. normal boiling point is a specific location on that line.

The normal boiling point occurs when the pressure of the atmosphere is 1 atm. So this particular point is the normal boiling point of water. whereas anywhere along this line is called the boiling point curve. Now, the normal melting point occurs at a pressure of 1 atm.

So, this is the normal melting point. And this is called the melting point curve. So, if you hear the word normal attached to melting point or boiling point, the pressure has to be 1 atm.

Transcript for:Understanding CO2 and Water Phase Diagrams

Transcript for:
Understanding CO2 and Water Phase Diagrams