If a supersaturated sugar solution is allowed to evaporate slowly, sugar crystals form in the container. Hence, sugar molecules go from a disordered form (in solution) to a highly ordered, crystalline form. Does this process violate the second law of thermodynamics? Explain.

Answer 1

No, this process does not violate the second law of thermodynamics. The second law states that the entropy (disorder) of an isolated system will either remain constant or increase over time. In this case, the formation of sugar crystals corresponds to a decrease in the entropy of the sugar molecules as they go from a disorderly arrangement in solution to an orderly arrangement as crystals.

However, this process does not involve an isolated system. The solution, which contains sugar molecules, is in contact with its surroundings, such as air. When water evaporates from the solution, heat is transferred from the solution to the environment. This evaporation and heat transfer to the surroundings results in an increase of entropy in the environment.

When considering the total entropy change of both the solution and the environment, it is seen that the increase in entropy due to heat transfer to the environment is much larger than the decrease in entropy due to the ordering of sugar molecules into crystals. Consequently, the overall entropy of the combined system (solution and environment) increases, satisfying the second law of thermodynamics. Thus, the process does not violate the second law.