The relationship between the solubility of potassium nitrate and the temperature of its solution is that as the temperature increases the solubility of potassium nitrate also increases. The solubility of potassium nitrate increases as the temperature increases because it is a solid and for most solids an increase in temperature results in greater solubility. This pattern occurs because increased temperature means increased molecular motion, which breaks apart the firm bonds holding the molecules in a solid together. When a solid comes in contact with a liquid solvent some of the molecules in a solid will break free and mix into the liquid. As more solute is added into the solvent, some of the molecules that broke free will return as they bump into the solid. When the solid has reached its maximum solubility the ratio between the number of molecules breaking free from the solid and attaching themselves to the solid is exactly the same. By increasing the temperature the molecules begin to move faster making it more likely for molecules on the surface of the solid to break free and less likely for molecules in the solution to become attached to the solid. Therefore, the addition of heat facilitates the dissolving reaction by providing energy to break the bonds in a solid and allowing the molecules to become detached.
The moment crystals begin to form, the saturation point of the solution is illustrated. When less solvent is present, the concentration of the solute quickly exceeds the solubility causing the excess solute to crystallize out.
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