Search results
Results From The WOW.Com Content Network
The degree of dissociation is the fraction of the original solute molecules that have dissociated.It is usually indicated by the Greek symbol .There is a simple relationship between this parameter and the van 't Hoff factor.
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
In case of very strong acids and bases, degree of dissociation will be close to 1. Less powerful acids and bases will have lesser degree of dissociation. There is a simple relationship between this parameter and the van 't Hoff factor. If the solute substance dissociates into ions, then
b c is the colligative molality, calculated by taking dissociation into account since the boiling point elevation is a colligative property, dependent on the number of particles in solution. This is most easily done by using the van 't Hoff factor i as b c = b solute · i, where b solute is the molality of the solution. [3]
The degree of dissociation is measured by determining the van 't Hoff factor i by first determining m B and then comparing it to m solute. In this case, the molar mass of the solute must be known. The molar mass of a solute is determined by comparing m B with the amount of solute dissolved.
Here K f is the cryoscopic constant (equal to 1.86 °C kg/mol for the freezing point of water), i is the van 't Hoff factor, and m the molality (in mol/kg). This predicts the melting of ice by road salt. In the liquid solution, the solvent is diluted by the addition of a solute, so that fewer molecules are available to freeze.
The standard enthalpy change can be determined by calorimetry or by using the van 't Hoff equation, though the calorimetric method is preferable. When both the standard enthalpy change and acid dissociation constant have been determined, the standard entropy change is easily calculated from the equation above.
i is the van 't Hoff factor, the number of particles the solute splits into or forms when dissolved. b is the molality of the solution. A formula to compute the ebullioscopic constant is: [2] = R is the ideal gas constant. M is the molar mass of the solvent.