Question

You seal a container half-filled with water. Which best describes what occurs in the container? a. Water evaporates until the air becomes saturated with water vapor; at this point, no more water evaporates. b. Water evaporates until the air becomes 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. The water evaporates until it is eventually all in vapor form. Justify your choice and for choices you did not pick, explain what is wrong with them.

Short answer

The best answer is choice d. Water evaporates, and then water evaporates and recondenses simultaneously and continuously. This is because once the air becomes saturated, evaporation and condensation will occur simultaneously, maintaining the state of saturation.

Step-by-step solution

Understand Key Concepts

Before we analyze each choice, let's understand a few key concepts: 1. Evaporation: The process by which liquid water turns into water vapor. 2. Saturation: A condition where the air cannot hold any more water vapor at a given temperature and pressure. If there is more vapor than the air can hold, it will condense back into liquid water. Now we will examine each choice based on these concepts.

Analyze Choice a

Choice a states that water evaporates until the air becomes saturated, and then no more water evaporates. This choice is correct up to the point where it mentions saturation. When the air becomes saturated with water vapor, the rate of evaporation would equal the rate of condensation. However, the water will continue to evaporate and condense at an equal rate, maintaining the state of saturation. So, choice a is partially correct.

Analyze Choice b

Choice b suggests that water evaporates until the air becomes overly saturated (supersaturated), and most of the water recondenses. The cycle continues until a certain amount of water vapor is present, and then the cycle ceases. This choice doesn't account for the fact that the rate of evaporation and condensation will equalize once saturation is reached. So, choice b is incorrect.

Analyze Choice c

Choice c claims that water does not evaporate because the container is sealed. This is incorrect. Although the container is sealed, water molecules can still escape the liquid surface and become vapor. The sealing of the container would only affect the air's capacity to hold water vapor, not the evaporation process itself.

Analyze Choice d

Choice d states that water evaporates and then evaporates and recondenses simultaneously and continuously. This choice is accurate as it suggests that once the air becomes saturated, evaporation and condensation will occur simultaneously, maintaining the state of saturation. So, choice d is the correct answer.

Analyze Choice e

Choice e claims that water evaporates until it is eventually all in vapor form. This choice is incorrect because, in a sealed container, the air will become saturated at some point, and the rate of evaporation will equal the rate of condensation, meaning that not all the water will turn into vapor. In conclusion, the best answer is: d. Water evaporates, and then water evaporates and recondenses simultaneously and continuously.

Key concepts

Evaporation

Evaporation is the process where molecules at the surface of a liquid gain enough energy to enter the gaseous state. This transformation occurs when the molecules escape from the liquid's surface into the air. In our everyday environment, this process can happen from any liquid surface when exposed to air.

• Evaporation increases with higher temperatures because heat provides the energy needed for molecules to break free.
• It also depends on the surface area — the more exposed the surface, the more evaporation can occur.
• In a sealed container, though, as water evaporates, some vapor remains trapped, influencing evaporation greatly. This leads us to consider the concept of saturation.

Understanding evaporation is crucial for grasping how climates are regulated and how simple things, like a puddle drying up, happen. It's a key part of the water cycle, ensuring that water moves from lakes, rivers, and oceans into the atmosphere to form clouds.

Saturation

Once evaporation occurs, water vapor accumulates in the air above the liquid. Saturation is reached when the air can no longer hold any more vapor at the current temperature and pressure.

• This happens because air has a limited capacity for vapor; once that limit is reached, the air is saturated.
• At saturation, the rates of evaporation and condensation are equal. This balance means that the amount of water in the gaseous state hovers around a constant value.
• In practical terms, this is why your bathroom mirrors fog up when you shower; the air quickly becomes saturated with steam.

In a closed system, like a sealed container, saturation dictates when the water vapor stops accumulating, maintaining a dynamic equilibrium with the liquid water it came from.

Condensation

Condensation is the opposite of evaporation. It's when water vapor transitions back into a liquid state. This process becomes significant when saturation is reached.

• Once the air is saturated, any additional water vapor condenses as it loses energy.
• Condensation is what causes clouds to form, dew on grass in the morning, or even the water droplets on the outside of a cold beverage.
• In a sealed container, condensation balances evaporation, so water continuously shifts between the vapor and liquid states while the total amount in each state remains constant.

This cycle of evaporation and condensation is crucial in nature's patterns, helping to form precipitation and regulate temperatures.

Closed Container

A closed container creates a controlled environment, an important concept when studying evaporation and condensation. In a sealed container partially filled with water, several things occur:

• Evaporation still happens initially as the water molecules escape the liquid surface.
• The space above the liquid initially allows vapor to accumulate until the air becomes saturated with vapor.
• Once saturation is achieved, the processes of evaporation and condensation occur at equal rates, resulting in a stable equilibrium.
• The key point is that even though further vapor formation is limited by saturation, the molecules continue to exchange phases without net changes in their amounts.

This environment helps in illustration and experimentation, showing how equilibrium states are reached and maintained, integral to understanding physical chemistry and the behavior of substances in various conditions.