A phase diagram is a graphical representation of the physical states that a substance can exist in under different conditions of temperature and pressure. The phase diagram for naphthalene, also known as mothballs, is a useful tool for understanding the behavior of this substance under different conditions.
Naphthalene is a white, crystalline solid with a strong, musty odor. It is commonly used as a moth repellent, but it has also been used as a raw material in the production of dyes, plastics, and explosives.
The phase diagram for naphthalene shows that it has a melting point of about 80°C. At temperatures below this point, naphthalene exists in the solid state. As the temperature increases, the solid naphthalene begins to melt and transform into a liquid.
The phase diagram also shows that naphthalene has a boiling point of about 218°C. At temperatures above this point, the liquid naphthalene vaporizes and transforms into a gas.
The phase diagram for naphthalene also shows the effect of pressure on the physical state of the substance. At low pressures, naphthalene exists in the gas phase at temperatures above its boiling point. As the pressure increases, the boiling point of naphthalene increases, and the substance exists in the liquid phase at higher temperatures.
In summary, the phase diagram for naphthalene shows that it exists in the solid state at temperatures below its melting point, in the liquid state at temperatures between its melting and boiling points, and in the gas state at temperatures above its boiling point. The phase diagram also illustrates the effect of pressure on the physical state of naphthalene, with higher pressures causing the substance to exist in the liquid phase at higher temperatures.
The Binary Phase Diagram Naphthalene
The phase rule predicts that for two phases to co-exist in a one-component system only one of the two variables can be chosen independently. In this case extrapolate back as shown in Figure 5. What information does the slope of a line in a phase diagram convey about the physical properties of the phases it separates? Possible cases are: a The system is a single phase e. Then you can pick out the relevant thermocouple values form your plots and convert these to temperatures. The phase diagram of carbon dioxide shows that liquid carbon dioxide cannot exist at atmospheric pressure.
A binary system consists of two components that can form solid solutions which could cover from one range to another. Further cooling will gradually crystallize more and more solid until the liquid is completely gone. Eight tubes of designated weight percent of naphthalene are provided. To calibrate the thermocouples. Even clearing streets of snow by "salting" is an example of the practical use of the freezing point depression effect. New York: McGraw-Hill Higher Education.
The temperature then falls again in a regular manner although with a different slope than for the case of the liquid. These curves define the temperatures and pressure at which two phases can co-exist in equilibrium. Consequently, solid carbon dioxide sublimes directly to a gas. Due to these imperfections, thermocouples should be calibrated by measuring the voltage with the measuring thermocouple set in some constants temperature bath e. From this phase diagram, it also becomes clear that a mixture of the two components changes phase melts or solidifies over a range of temperatures, not at a single temperature as a pure substance. The one-component phase diagram for water. The Phase Diagram of Carbon Dioxide In contrast to the phase diagram of water, the phase diagram of CO 2 2 cannot exist at pressures lower than 5.
Along this line, the solid is in equilibrium with the vapor phase through sublimation and deposition. To accomplish that, fill a capillary tube with crystals about 3 mm high by placing the capillary tube open end down into the sample powder and tapping it to get the crystals into the tube. This graph is difficult to draw. For example if a salt solution is cooled sufficiently the system will exist as a mixture of salt crystals and ice crystals. It is simple to deduce the physical state of a binary system once the temperature and composition of the system have been defined. The melting points of the two pure components T m,A for A and T m,B for B are also noted.
Phase Equiliubrium of Naphthalene and Biphenyl Mixture Essay Example
Here there is no degree of freedom. Thermal analysis refers to techniques that is solely based on the idea of thermal control 1. The temperature can easily rise by a few degrees when the beaker is only half filled with ice. A A graphic summary of the physical state of a substance as a function of temperature and pressure in a closed system. Clamp the tubes and allow them to cool in air and start recording thermocouple voltages.
This is simply a saturated solution along with some precipitate. Ruoff Electrochemical Society Proceedings, 94-24, NJ, 1994 p. The cooling will only continue after the solid formation is complete. Phase diagrams contain discrete regions corresponding to the solid, liquid, and gas phases. Although this explanation is intuitively satisfying, it is incorrect, as we can show by a simple calculation. If the temperature is lowered until it reaches the line BC, the 2-phase region is entered. The theory is found on page 204 of Atkins.
For example, if the solid—liquid line slopes up and to the right, the liquid is less dense than the solid, while if it slopes up and to the left, the liquid is denser than the solid. At the eutectic temperature, the solution is saturated with respect to both components so that both a and b start to precipitate. The solid and liquid regions are separated by the melting curve of the substance, and the liquid and gas regions are separated by its vapor pressure curve, which ends at the critical point. To simplify matters the pressure is fixed at some value and a 2 dimensional temperature vs composition diagram is used. Handbook of Chemistry and Physics. The area below the horizontal line represents systems whose composition and temperature are such that the system exists as a physical mixture not a solution of solid A and solid B. A phase diagram is a diagram from which the physical state of a system may be deduced once the temperature, pressure and composition of the system have been defined.
With the data retrieved from the equation, the enthalpy of fusion can be calculated using the following equation, 1. It is much better to increase the temperature slowly than to try and cool the system down while looking through the magnifying glass of the apparatus. Cite this article Hidalgo-Ouesada, R. Do not stop taking readings at this point since the temperature should rise again. Phase Diagram of Naphthalene-Biphenyl Phase diagrams are of considerable practical utility. Zimmerman, in Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, edited by K.
Ruoff Electrochemical Society Proceedings, 94-24, NJ, 1994 p. With increasing temperature, the binary mixtures undergo structural changes corresponding to those of pure n-pentacosane, while naphthalene seems to retain its initial crystalline structure until fusion occurs. To simplify matters the pressure is fixed at some value and a 2 dimensional temperature vs composition diagram is used. Since the pressure is fixed in phase diagrams like the one above, only one degree of freedom is used up. The slope of the line separating two phases depends upon their relative densities. A phase diagram is a diagram from which the physical state of a system may be deduced once the temperature, pressure and composition of the system have been defined. The relation of cooling curves at different concentrations to the phase diagram.
