Pvt behaviour

PVT Behaviour prepared by Muhammad Awais Sharif..

1. PVT Behavior Prepared by: Awais Sharif Comsats Lahore

2. P-V-T Behavior of Pure Substances PT Diagram A typical P-T diagram showing the relationship between pressure and temperature of a pure substance is shown below:

3. PT Diagram The three lines 1-2, 2-3 and 2-C display conditions of P and T at which two phases may co-exist in equilibrium, and are boundaries for the single-phase regions of solid, liquid and vapor (gas).

4. Graph Explanation Line 1-2 is known as the sublimation curve, and it separates the solid from the gas regions. Line 2-3 is known as the fusion curve, and it separates the solid and liquid regions. Line 2-C is known as the vaporization curve, and it separates the liquid and the gas regions. All three lines meet at Point 2, known as the Triple Point. This is a point where all 3 phases can co-exist in equilibrium.

5. C ritical P ressure and Critical Temperature The pressure and temperature corresponding to this point(Critical Point) are known as the critical pressure PC and critical temperature TC respectively. These are the highest pressure and temperature at which a pure substance can exist in vapor-liquid equilibrium. The shaded area shows the area existing at pressure and temperature greater than P and T. This region is called the fluid region.

6. Explanation The gas region is sometimes divided into two parts, as indicated by the dotted vertical line through temperature TC. A vapor region is the region to the left of this line and represent a gas that can be condensed either by compression at constant temperature or by cooling at constant pressure. The region everywhere to the right of this line, including the fluid region, is termed supercritical.

7. P-V Diagram for Pure Substance The P-T Diagram does not provide any information about volume. It merely displays the phase boundaries on as a function of pressure and temperature. On the P-V Diagram, the triple point appears as a horizontal line, where all 3 phases co-exist at a single temperature and pressure.

8. P-V Diagram

9. P-V Diagram Isotherms are lines of constant temperature and these are superimposed on the P-V Diagram as shown in the Figure.

10. Explanation Point C is the critical point. VC is the critical volume at this point. The isotherm labeled T > TC does not cross a phase boundary. The lines labeled T1 and T2 are isotherms for subcritical temperatures, and they consist of 3 segments.

11. Continue.. The horizontal segment of each isotherm represents all possible mixtures of liquid and vapour in equilibrium, ranging from 100% liquid at the left end (curve B-C) to 100% vapour at the right end (curve D-C). Curve B-C represents saturated liquid at their boiling points, and curve D-C represent saturated vapours at their condensation points.

12. PV Diagram (Continue) Subcooled liquid and superheated vapour regions lie to the left and right, respectively. Subcooled liquid exists at temperatures below the boiling point for the given pressure. Superheated vapour exists at temperatures above the boiling point for the given pressure

13. PV Diagram (Continue) Isotherms in the subcooled liquid region are very steep, because liquid volumes change little with large changes in pressure. The horizontal segments of the isotherms in the 2-phase region become progressively shorter at higher temperatures, being ultimately reduced to a point at C, the critical point.