Another example for crystalline candy is rock candy. To make rock candy, we use more sugar than it could dissolve in water at room temperature. For instance, we can add three cups of sugar into one cup of water. In order to allow all the sugar to dissolve, we have to boil the water to increase the temperature. By increasing the temperature, the dissolving process will simultaneously increase. The solution is heated until no more sugar can dissolve. Then, the sugary solution is left to cool down for several days to allow huge crystals of sugar to form.
So what happens when the solution finally cools down? Once it cools down, it becomes a supersaturated solution. A supersaturated solution is unstable as it contains more solute. As the temperature decrease, sugar crystals are formed. This crystallization process can be explained by the Le Châtelier’s principle; which states that if a system is shifted away from its equilibrium, the system will restores its equilibrium by reacting in opposition to the shift. Thus, a decrease in temperature causes a system to produce energy, to bring the temperature up. This is because when the chemical bonds are formed, energy is released. Therefore, more sucrose molecules will join the crystal in an attempt to increase the temperature. This explains the formation of crystals when the temperature decreases. In short, the lower the temperature, the more sucrose molecules join the sugar crystals, and that is how rock candy is made.