Freezing, Melting and Boiling Point                                        pv diagram
        Water is special because it can have three states of matter exist in equilibrium at one single temperature. This circumstance is called a triple point, where the phase change lines meet up at one point on a Pressure vs Volume graph. The temperature where the triple point of water is said to be 0.00 degrees Celsius. The triple point of water is used to define the kelvin, the base unit of thermodynamic temperature in the International System of Units (SI). "The triple point of water is the standard fixed-point temperature for the calibration of thermometers. This agreement also sets the size of the kelvin as 1/273.16 of the difference between the triple point temperature of water and absolute zero" (). All three states of matter can exist in equilibrium because of vapor pressure.
         Vapor pressure is defined as the pressure at which a gas coexists with its solid or liquid phase. It can also be defined as the pressure a gas would create if it occupied the total volume available. Dalton's law of partial pressures says that in a mixture of gases, each gas will exert its own pressure on the other gases in a confined volume. The total sum of the pressure is the sum of all individual partial pressures.


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Cohesion & Adhesion
Water & Light