Question

Consider a sealed container half-filled with water. Which statement best describes what occurs in the container?

a. Water evaporates until the air is saturated with water vapor; at this point, no more water evaporates.

b. Water evaporates until the air is overly saturated (supersaturated) with water, and most of this water recondenses; this cycle continues until a certain amount of water vapor is present, and then the cycle ceases.

c. The water does not evaporate because the container is sealed.

d. Water evaporates, and then water evaporates and recondenses simultaneously and continuously.

e. Water evaporates until it is eventually all in vapor form. Explain each choice, and justify the best choice. For those you did not choose, explain why they are incorrect.

Short answer

Consider a sealed container half-filled with water. Here, statement A best describes the container among the five statements.

Step-by-step solution

Explanation regarding part (a)

In this case, it has been stated that water will evaporate until the air becomes saturated with water vapor. And then, if the saturation point is reached, there will be no more evaporation of water. Generally, water will evaporate into the vapour phase and then that water in the vapor phase will condense back down into the liquid phase until equilibrium is achieved. If equilibrium is achieved, the air cannot hold any more water vapor and as a result, it becomes saturated with that water vapor. So, it seems that part A is an accurate explanation regarding the process.

Explanation regarding part (b)

Here, it depicts that the water evaporates until the air becomes supersaturated with water vapor and then water condenses back into the liquid state. This is a cycle of evaporation condensation that continues until a certain amount of water is present in the air, and then it ceases. If air becomes supersaturated with water vapor, then all of the liquid molecules are transferred into the air to a point where it achieves the saturation point. It results in the evaporation of the maximum amount of water vapor that air can hold. Since this container is only half filled, it seems that it would be unlikely to achieve supersaturation because we know that air, which is a gas, its particle spread out a lot further than the liquid form of water. If the air were able to hold more water vapour than its saturation state, then we would most likely have more than half of the container filled with air because then these gas particles spread out and fill a large portion of the volume. Therefore, this theory regarding part (b) is less likely than that of part (a).

Explanation regarding part (c)

In this case, it says that water will not evaporate as the container is sealed. Though the container is indeed sealed, there will be air in the other half of that container as this is not a vacuum. If there were no air in that container, then water will not evaporate. As air is present inside the container, water will naturally evaporate into the vapour phase. So, statement (c) does not make sense.

Explanation regarding part (d)

Here, for part d, it says that water will evaporate, and then it will continue a cycle of simultaneous evaporation and condensation. So, if we consider this case, that water will evaporate into the air, and then that vapor state of the water will re condense back down into the liquid state. And these will keep happening continuously. It cannot be true. This is a continuous cycle of evaporation and condensation, which is basically a form of rain inside the container, and it is known that this process does not occur naturally. Therefore, the theory regarding part (d) is not favourable.

Explanation regarding part (e)

In this case, it states that water evaporates until it is all in vapor form. This is similar to part b because, in part b, the air would become supersaturated with water vapor. But it is known that this does not make sense as the container is only half filled with air. If we take the extreme of this case, then the air would be against supersaturated because it would hold all of the initial half-filled liquid in this container, and it will exceed its saturation point. And it doesn't make physical sense for air to be able to hold all of that water vapor inside a container that only contains half air initially. So, it can be stated that part (e) also does not make any sense.