Question

You may have noticed that when water boils, you can see bubbles that rise to the surface of the water. Which of the following is inside these bubbles? Explain. a. air b. hydrogen and oxygen gas c. oxygen gas d. water vapor e. carbon dioxide gas

Short answer

The correct answer is (d) water vapor. The bubbles formed during boiling are due to water molecules escaping the liquid phase and entering the gas phase, and the boiling process does not produce other gases like oxygen or carbon dioxide. Therefore, the bubbles primarily consist of water vapor.

Step-by-step solution

Understand the process of boiling water

When water is heated, the molecules absorb heat and gain energy. This leads to an increase in their kinetic energy, causing the molecules to vibrate and move around more rapidly. As the temperature of the water continues to rise, the molecules eventually have enough energy to break free from the liquid state and enter the gas phase. This process is known as boiling.

Understand the composition of the bubbles

The bubbles formed during boiling are due to water molecules escaping the liquid-phase and entering the gas-phase. When this happens, they combine to form pockets of gaseous water molecules, otherwise known as water vapor. Since the boiling process does not involve chemical reactions that would produce other gases like oxygen or carbon dioxide, the main component of these bubbles is water vapor.

Choose the correct option

From the understanding of the boiling process and the composition of the bubbles formed during boiling, we can now determine the correct option among the given choices: a. air b. hydrogen and oxygen gas c. oxygen gas d. water vapor e. carbon dioxide gas Based on our analysis, the correct answer is (d) water vapor, as the bubbles primarily consist of water molecules that have entered the gas-phase due to the boiling process.

Key concepts

Water Molecules

When we think about water, we imagine a cool glass of liquid that quenches our thirst or a calm lake. But let's dive into what's happening on a microscopic level. In its liquid form, water is composed of countless tiny particles called water molecules. Each water molecule consists of two hydrogen atoms and one oxygen atom, chemically bonded to form H₂O. These nifty little molecules love to move and wiggle around. They're always in motion, whether they're in your glass or swirling in the sea.

In their liquid state, water molecules are quite friendly. They stick relatively close together thanks to some fancy forces called hydrogen bonds. These bonds keep the molecules from flying apart, allowing water to maintain its liquid form until it's heated. Imagine these bonds as invisible strings that keep the molecules dancing together as partners.

Gas Phase

As you heat water, you're giving those water molecules a bit of a nudge. With enough heat, these little guys gain so much energy that they start bouncing around more vigorously than ever. Eventually, they reach a point where those hydrogen bonds aren't strong enough to hold them together anymore. This is when the molecules transition from the liquid state into the gas phase.

In the gas phase, water molecules are free from the close-knit structure of the liquid state. They drift apart, spreading out and filling the available space. This transition is what we observe as boiling. The change isn't a gradual slide but more of a liberation of the molecules, where they transform into a more energized and less ordered state.

Water Vapor

Once water molecules make their way into the gas phase, they form what we know as water vapor. Water vapor is simply gaseous water, but it can sometimes be a bit tricky to see. However, during boiling, we can observe it quite clearly when bubbles rise to the surface. These bubbles are collections of water molecules in vapor form.

This transformation into water vapor is a natural part of the boiling process. When you boil a pot of water and see those bubbles vigorously bubbling up, you’re witnessing water molecules escaping into a less dense and more expanded form. Unlike other gases, water vapor is purely the result of the water molecules themselves; no other substances are involved in this transition. So next time you observe boiling, remember: it's just water having some fun in the gas phase!

Kinetic Energy

Kinetic energy is a key player in the process of boiling. Simply put, it's the energy that an object has due to its motion. In the case of water molecules, kinetic energy is what drives them to move around and eventually break free from the liquid.

When you apply heat to water, you're essentially giving its molecules more kinetic energy. This makes them start to jiggle and dance more rapidly. With sufficient kinetic energy, the molecules overcome the attractive forces that keep them in liquid form. This is similar to dancers moving so energetically that they break out into a more spacious dance floor — in this case, entering the gas phase.

Without kinetic energy, water molecules wouldn't have the propensity to change states. It's the engine driving the transformation from liquid to gas, the key that unlocks water vapor from its liquid bounds.