Problem 27 - Chemistry

Question

When wet laundry is hung on a clothesline on a cold winter day, it will freeze but eventually dry. Explain

Step-by-Step Solution

Answer

Wet laundry hung out on a cold winter day dries due to the process of sublimation, in which the ice crystals formed in the fabric transform directly into water vapor, bypassing the liquid phase. This occurs under certain temperature and pressure conditions, with low temperatures and atmospheric pressure facilitating sublimation. As the ice crystals sublimate, the water content in the laundry decreases until it eventually dries.

Step 1: Understand the states of water

First, we need to understand the three states of matter for water: solid (ice), liquid (water), and gas (water vapor). When water changes its state, it undergoes a phase change. There are different phase changes in which water can transform, such as melting, freezing, evaporation, and sublimation.

Step 2: Learn about sublimation

Sublimation is a process in which a solid substance directly transforms into its gaseous state without passing through the liquid phase. In the case of wet laundry, the water molecules in the clothing will undergo sublimation when exposed to the cold winter air.

Step 3: Understand the role of temperature and pressure

The process of sublimation occurs under certain temperature and pressure conditions. In winter, the temperature is often below the freezing point of water (0 degrees Celsius or 32 degrees Fahrenheit), and the atmospheric pressure is low. It's important to note that the lower the atmospheric pressure, the easier it will be for sublimation to occur.

Step 4: Recognize the role of ice crystals in sublimation

When wet laundry is hung out on a cold winter day, the water in the fabric will freeze and form ice crystals. These ice crystals are exposed to the cold, dry air. Due to the difference in vapor pressure between the ice and the air, the water molecules in the ice crystals will transform directly into water vapor, bypassing the liquid phase, through the process of sublimation.

Step 5: Observe the drying process of wet laundry

As the ice crystals sublimate, the water content in the wet laundry decreases over time. Eventually, the laundry will become dry as most of the water molecules have been transformed into water vapor and released into the air through the process of sublimation. In conclusion, the process of sublimation is responsible for the drying of wet laundry when hung on a clothesline on a cold winter day. Although the laundry initially freezes, the ice crystals directly transition into water vapor due to the temperature and pressure conditions, leading to the eventual drying of the laundry.

Key Concepts

Phase Changes

Water, like many substances, can exist in different states—solid, liquid, and gas. These states are affected by temperature and pressure, leading to various phase changes. Key phase changes for water include melting, freezing, evaporation, and sublimation. Each phase change involves a shift in energy and molecular arrangement, allowing for the transformation from one state to another.

• Melting: When a solid (ice) turns into a liquid (water) as the temperature rises.
• Freezing: The reverse of melting, where water turns into ice as the temperature drops.
• Evaporation: Liquid water turns into gas as it gains energy.
• Sublimation: The direct transition from a solid form (like ice) to a gaseous form (like water vapor) without becoming liquid first.

Understanding these changes helps explain natural phenomena, like how wet laundry can dry even in freezing temperatures.

Solid to Gas Transition

Sublimation is the process where a substance directly transitions from a solid to a gas without passing through the liquid phase. This can occur under specific conditions of low temperature and pressure. In nature, we often observe this when frost or snow gradually disappears even when the temperature remains below freezing.

When laundry is hung out in the cold, water in clothing may freeze into ice, becoming solid. Then, instead of melting into liquid water due to cold temperatures, these ice molecules can sublimate directly into water vapor. The transition is energy-intensive but is facilitated because the air surrounding the frozen laundry is typically cold and dry, aiding sublimation. This fascinating transition is integral in diverse environmental processes and industrial applications.

Drying Process

On a cold winter day, laundry can indeed dry outside despite freezing temperatures. This drying is facilitated by sublimation—a drying process where ice turns directly into water vapor. The frozen water molecules in the clothes respond to the surrounding cold, dry air, encouraging sublimation.

This process can be broken down into several important steps:

• Formation of Ice Crystals: Initially, water in the laundry freezes, forming ice.
• Exposure to Atmosphere: The ice is exposed to cold air with low atmospheric pressure, which helps initiate sublimation.
• Sublimation into Vapor: The ice crystals transform into water vapor and dissipate into the air, bypassing the liquid phase entirely.
• Evaporation Completes: Over time, the loss of water vapor from the fabric results in the laundry becoming dry.

This process elucidates how laundry can dry even when traditional drying methods seem unfeasible, illustrating the critical role of sublimation in our everyday lives.