So I know that for water to boil the vapor pressure has to be equal to atmospheric pressure. Does this mean that as the pressure increases, a substance becomes more gaseous? Then why is CO2 liquid at high pressures?
In: Chemistry
>Does that mean that as the pressure increases, a substance becomes more gaseous?
No. The opposite. The higher the pressure, the more likely the fluid will become liquid or even solid.
For the water example, you’re trying to get the vapor pressure of the water to match the ambient pressure. If you’re increasing the pressure, you’re not increasing the vapor pressure, but the ambient pressure. You can only increase the vapor pressure of the water by heat. So if you increase the pressure in the container, like a pressure cooker, water must heat up further before it can boil; the vapor pressure has to go even higher than usual in order for it to meet the ambient (within the pressure cooker) pressure.
The same thing happens in the other direction for carbon dioxide. When the ambient pressure increases, the vapor pressure of the carbon dioxide is staying the same. Once the ambient pressure is higher than the vapor pressure, the carbon dioxide begins to condense into liquid; it is now below its boiling point.
Same for water. Increased pressure keeps it in a liquid state. This is why water boils in a vacuum because relative pressure is much lower.
The pressure of the system is what matters in relation to the fluid material.
As pressure increases, materials prefer to be denser states of matter. Ice may become water, while most liquids become solids, and gases become liquids or solids.
No, you have it backward. Higher pressure = you need more vapor pressure to boil = things tend to stay liquid at higher temps.
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