phase diagram

2006 Words5 Pages

Introduction:

Chemical equilibrium is a crucial topic in Chemistry. To represent and model equilibrium, the thermodynamic concept of Free energy is usually used. For a multi-component system the Gibbs free energy is a function of Pressure, Temperature and quantity (mass, moles) of each component. If one of these parameters is changed, a state change to a more energetically favorable state will occur. This state has the lowest free energy. When the free energy of all states are equal to each other, the system is at equilibrium. The Heat that is relased or absorbed during a state change absorbed is known as latent heat. For a binary mixture such as durene and naphthalene, the Clausius-Clapeyron equation (cf. Appendix) relates the latent heat of fusion or solidification to the rate of change of melting point with pressure. Also when a mixture is cooled its latent heat changes. Since the molar volume change resulting from state change (i.e liquid to solid) is minimal, phase equilibrium is independent of of pressure and depends only on composition and temperature. Therefore by studying a system at different temperatures and various compositions, it should be possible to observe and predict phase changes in that system.

Methods:

To complete the binary phase experiment, students first set up the experimental apparatus, which consisted of a stir plate, ring stand, Erlenmeyer flask, ice water bath, and a GLX temperature probe. The temperature probe was set to take a data point every second. A stir bar was added to the ice water bath to ensure a uniform temperature throughout the bath, and thus more uniform cooling of the samples. A beaker of boiling water was set up on a hot plate in order to melt the samples. After adjusting t...

... middle of paper ...

... lowest temperature where liquid phase is in equilibrium with solid phase.

Phase diagrams are means that can be used to graphically represent the thermal behavior of mixtures by studying the compositions and temperatures at which particular phases exist, equilibrium curves, and the eutectic point. The diagram has composition on the x axis and temperature on the y-axis at a specific pressure. The equilibrium curves are the phase boundaries of the system. All the systems system studied were at constant pressure, so according to Gibb's Phase rule the degree of the freedom of the system in this case is F = 1 + C - P = 3 - P. Therefore, there is a maximum of 3 phases present in the binary system. At the eutectic point, all 3 distinct phases are in equilibrium consequently the degree of the freedom of the system is now F = 3-3 = 0. In sum, the eutectic point is fixed.

More about phase diagram

Open Document