Phase Diagrams - Chemistry LibreTexts
equation of state is represented by a surface in a three dimensional system (P, V, T), but its two-dimensional projections, i.e., (P, T) or (P, V), are most often used. Phase Diagrams. The figure below shows an example of a phase diagram, which summarizes the effect of temperature and pressure on a substance in a closed. 2 Carbon Dioxide (CO2) pressure-temperature phase diagram showing the triple point . The results on the left figure were obtained for an Aspect Ratio of
A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance.
These diagrams indicate the physical states that exist under specific conditions of pressure and temperature, and also provide the pressure dependence of the phase-transition temperatures melting points, sublimation points, boiling points.
The physical state of a substance and its phase-transition temperatures are represented graphically in a phase diagram. The pressure and temperature axes on this phase diagram of water are not drawn to constant scale in order to illustrate several important properties. We can use the phase diagram to identify the physical state of a sample of water under specified conditions of pressure and temperature.
Note that on the H2O phase diagram, the pressure and temperature axes are not drawn to a constant scale in order to permit the illustration of several important features as described here. The physical properties of water under these conditions are intermediate between those of its liquid and gaseous phases. This unique state of matter is called a supercritical fluid, a topic that will be described in the next section of this module. These temperature-pressure data pairs correspond to the sublimation, or deposition, points for water.
Thus, if we place a frozen sample in a vacuum with a pressure less than 0. Freeze-dried foods, like this ice cream, are dehydrated by sublimation at pressures below the triple point for water.
Carbon dioxide (data page) - Wikipedia
Note that this curve exhibits a slight negative slope greatly exaggerated for clarityindicating that the melting point for water decreases slightly as pressure increases. Summary Skills to Develop To understand the basics of a one-component phase diagram as a function of temperature and pressure in a closed system. To be able to identify the triple point, the critical point, and four regions: The state exhibited by a given sample of matter depends on the identity, temperature, and pressure of the sample.
A phase diagram is a graphic summary of the physical state of a substance as a function of temperature and pressure in a closed system. Each region corresponds to the range of combinations of temperature and pressure over which that phase is stable.
The combination of high temperature and high pressure upper right corresponds to a supercritical fluid. The lines in a phase diagram correspond to the combinations of temperature and pressure at which two phases can coexist in equilibrium.
The solid and liquid phases are in equilibrium all along this line; crossing the line horizontally corresponds to melting or freezing. The line that connects points A and B is the vapor pressure curve of the liquid, which we discussed in Section It ends at the critical point, beyond which the substance exists as a supercritical fluid.
The line that connects points A and C is the vapor pressure curve of the solid phase. Along this line, the solid is in equilibrium with the vapor phase through sublimation and deposition. Because no more than three phases can ever coexist, a phase diagram can never have more than three lines intersecting at a single point.
File:Carbon dioxide pressure-temperature phase diagram.svg
In practice, however, the conclusions reached about the behavior of a substance in a closed system can usually be extrapolated to an open system without a great deal of error. Far more reproducible than the melting point of ice, which depends on the amount of dissolved air and the atmospheric pressure, the triple point The triple point also represents the lowest pressure at which a liquid phase can exist in equilibrium with the solid or vapor.
At pressures less than 0.P-T diagram ( Pressure-Temperature diagram) in Hindi Properties of pure substances-4)
When a solid is heated at constant pressure, it melts to form a liquid, which eventually boils to form a gas. Phase diagrams can be used in several ways. We can focus on the regions separated by the lines in these diagrams, and get some idea of the conditions of temperature and pressure that are most likely to produce a gas, a liquid, or a solid.
We can also focus on the lines that divide the diagram into states, which represent the combinations of temperature and pressure at which two states are in equilibrium. The points along the line connecting points A and B in the phase diagram in the figure above represent all combinations of temperature and pressure at which the solid is in equilibrium with the gas.
At these temperatures and pressures, the rate at which the solid sublimes to form a gas is equal to the rate at which the gas condenses to form a solid. It contains all of the combinations of temperature and pressure at which the liquid boils. At every point along this line, the liquid boils to form a gas and the gas condenses to form a liquid at the same rate. At every point along this line, the solid melts at the same rate at which the liquid freezes.