If a bowl of salt water is left in the sun long enough for the water to evaporate a layer of salt crystals will be left in the bottom of the bowl. Salt crystals are more ordered than dissolved ions.
a. Is this an increase or decrease in entropy? Support your answer.
b. How does this increase or decrease relate to the second law of thermodynamics?
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a. This process represents a decrease in entropy. Entropy is a measure of the randomness or disorder in a system. In the case of a bowl of saltwater, when it is left in the sun and the water evaporates, the dissolved salt ions come together and form salt crystals at the bottom of the bowl. The formation of these salt crystals represents a more ordered arrangement compared to the random distribution of dissolved ions in the water. Therefore, the system becomes more ordered, and as a result, the entropy decreases.
b. This decrease in entropy is in line with the second law of thermodynamics, which states that the entropy of an isolated system tends to increase over time. In this situation, as the water evaporates and the salt crystals form, the system becomes more ordered and less random. However, it is important to consider the overall system, which includes both the saltwater and its surroundings. The entropy of the entire system, including the heat transfer and energy changes involved in the evaporation process, will still increase due to the dissipation of heat into the surroundings. So, while the decrease in entropy of the saltwater system is occurring, it is counterbalanced by an overall increase in entropy of the entire system, satisfying the second law of thermodynamics.