The Thermodynamics Of Potassium Nitrate Essay

1221 Words Nov 15th, 2016 5 Pages
The Thermodynamics of Potassium Nitrate Dissolving in Water

Introduction:

This experiment focuses on thermodynamics or the study of heat and molecular randomness. It helps illustrate how and why potassium nitrate (KNO3) dissolves in water. When it dissolves, it dissociates into potassium (K+) and nitrate (NO3-) ions. These ions can also recombine into solid potassium nitrate. This reaction can reach a state where concentrations of ions remain constant or Ksp; which stands for the equilibrium concentration for the solubility product. The solubility of a compound changes with temperature, so Ksp changes too. Thermodynamics focuses on three large areas; which are enthalpy, entropy, and free energy. Enthalpy change or ΔH, for KNO3 dissolving in water provides the difference in energy between solid potassium nitrate and its dissolved ions. Heat must be added for KNO3 to dissolve. Entropy change or ΔS, indicates the relative disorder of the ions. Free energy change or ΔG indicates whether the process is spontaneous or not. This can be calculated from ΔG = -RTlnKsp where R is the constant 8.314 J/K*mol, T is the temperature in kelvins, lnKsp is the natural logarithm of the equilibrium constant of the solubility product. We relate this to the Gibbs-Helmholtz equation -RTlnKsp = ΔH – TΔS, which can be rearranged to form a straight line, such as y = mx + b. Measuring the solubility of potassium nitrate in water at several temperatures will allow Ksp, ΔG, ΔH, and ΔS to be…

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