Problem 99 - Chemistry Matter and Change

Question

What process takes place in each situation? (Chapter 12\()\) a. a solid air-freshener cube getting smaller and smaller b. dewdrops forming on leaves in the morning c. steam rising from a hot spring d. a crust of ice forming on top of a pond

Step-by-Step Solution

Answer

a. Sublimation b. Condensation c. Evaporation d. Freezing (solidification)

Step 1: a. Solid air-freshener cube getting smaller and smaller

In this situation, the solid air-freshener is gradually changing its state from solid to gas. This process skips the liquid state, and the transition directly occurs between solid and gas states. This process is known as sublimation.

Step 2: b. Dewdrops forming on leaves in the morning

The water vapor present in the atmosphere changes its state from gas to liquid when it comes into contact with the cold surface of leaves in the morning. This process, where gas turns into liquid, is called condensation. In this situation, dewdrops are formed on leaves due to the condensation process.

Step 3: c. Steam rising from a hot spring

In a hot spring, water is heated to high temperatures, causing the water molecules to gain energy and change their state from liquid to gas. This process of turning liquid into gas is called evaporation. In this situation, the steam is rising from the hot spring due to the evaporation process.

Step 4: d. A crust of ice forming on top of a pond

In this situation, the water in the pond loses heat energy to the surroundings, causing it to change its state from liquid to a solid (ice). This process where a liquid turns into a solid is called freezing or solidification. In this case, a crust of ice is formed on top of a pond due to the freezing process.

Key Concepts

Sublimation

Sublimation is a fascinating phenomenon where a substance transitions directly from a solid state to a gas state, bypassing the liquid phase entirely. It's like watching a magician make something vanish into thin air—a solid seems to disappear without ever becoming a liquid.

An everyday example of sublimation occurs with dry ice, which is solid carbon dioxide. When exposed to room temperature, dry ice turns into a cloud of CO2 gas, skipping the liquid form. But it's not just a party trick; sublimation has real-world applications, such as in freeze-drying food, where water is removed from frozen food through sublimation, preserving the food for longer periods by preventing microbial growth.

Condensation

Condensation is the process by which a gas turns into a liquid. It's essentially gas getting cold feet and deciding to settle down into liquid droplets. This phase change usually occurs when a gas cools to the point where it can no longer hold all its water vapor, which then condenses into liquid form.

A simple way to visualize condensation is when you see dew forming on grass in the early morning or when your bathroom mirror fogs up during a hot shower. The water vapor in the air meets the cooler surface of the grass or the mirror and turns back into liquid water, clinging to the surface in tiny droplets. This process not only makes our mornings prettier with dew but is also crucial for the water cycle, bringing water back to Earth's surface.

Evaporation

Evaporation is like the gentle escape of molecules from a liquid to a gas. It happens when the molecules at the surface of a liquid gain enough energy to break free and become a gas. This can happen at any temperature, not just at the boiling point, which is why even on a lukewarm day, you might find a puddle of water slowly shrinking.

The energy for evaporation can come from the sun or the surrounding air. When you sweat, your body uses evaporation to cool you down; the sweat on your skin absorbs your body heat and then evaporates, leaving you feeling cooler. Large-scale evaporation from oceans and lakes is also a key step in Earth's water cycle, replenishing the atmosphere with water vapor that eventually falls as precipitation.

Freezing

Freezing, also referred to as solidification, is what happens when liquid gets so cold that it becomes solid. Imagine water turning into ice—a transition we often see in our daily lives, from freezing trays in our freezers to entire lakes solidifying in winter.

During freezing, the energy (as heat) is removed from the liquid, which slows down the motion of molecules to the point where they lock into a solid structure. This change not only provides us with ice cubes to cool our drinks but is also essential in shaping Earth's landscapes, as water expands when it freezes, causing cracks in rocks and forming unique geological features over time.