# Physical state given the critical temperature and critical pressure

• A13235378
In summary, the conversation discusses the use of the Antoine equation to find the saturation pressure of two substances, H2O and CH3OH, at a given temperature and pressure. The speaker also mentions they are having trouble finding the correct scale on a phase diagram to locate the point. They suggest using a log scale to plot the pressure.

#### A13235378

Moved from a technical forum, so homework template missing
Summary:: I have two substances H2O and CH3OH given at a temperature T and pressure P.

I also have critical temperatures and pressures.

How can I find the physical states of these substances.

My teacher recommended me to use the Antoine equation and find the saturation pressure, but I can't see how it can help me. I tried it on a phase diagram, but I couldn't find one that would provide the right scale. I can't find exactly where the point is.

You will have to provide a more complete description of the problem you are trying to solve.

A13235378 said:
Summary:: I have two substances H2O and CH3OH given at a temperature T and pressure P.

I also have critical temperatures and pressures.

How can I find the physical states of these substances.

My teacher recommended me to use the Antoine equation and find the saturation pressure, but I can't see how it can help me. I tried it on a phase diagram, but I couldn't find one that would provide the right scale. I can't find exactly where the point is.
Have your graphics package plot the pressure on a log scale.

## 1. What is the critical temperature?

The critical temperature is the temperature at which a substance transitions from a liquid to a gas phase at the critical pressure. Above this temperature, the substance cannot exist in a liquid state regardless of the pressure applied.

## 2. What is the critical pressure?

The critical pressure is the minimum pressure required to liquefy a gas at its critical temperature. At this pressure, the substance exists in a state where the liquid and gas phases are indistinguishable.

## 3. How does the physical state change at the critical temperature and pressure?

At the critical temperature and pressure, the substance exists in a state known as the critical point. At this point, the substance has properties of both a liquid and a gas, and there is no clear distinction between the two phases.

## 4. What happens if the temperature or pressure is above the critical point?

If the temperature is above the critical point, the substance will exist only in a gas phase regardless of the pressure applied. If the pressure is above the critical point, the substance will exist only in a liquid phase regardless of the temperature.

## 5. How is the critical temperature and pressure determined?

The critical temperature and pressure are determined experimentally by observing the behavior of a substance as temperature and pressure are varied. The critical point is where the substance undergoes a phase transition from a liquid to a gas, or vice versa, and the critical temperature and pressure can be calculated from these observations.