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Evaporation as Physical Change — Reading Comprehension

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MS-PS1-4

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This middle school science passage examines the process of evaporation, a fundamental physical change where a liquid turns into a gas at the surface. Aligned to NGSS MS-PS1-4, the passage provides a mechanistic explanation of evaporation, including how temperature, surface area, humidity, and air movement influence the rate of evaporation. Students will connect observable phenomena—like puddles drying after rain—to the underlying science, and explore examples ranging from wet hair drying to clothes hanging on a line. The passage integrates academic vocabulary and multiple scientific concepts, while activities such as comprehension questions, writing prompts, and graphic organizers support deep understanding. Audio integration is included for accessibility. This resource is ideal for grades 6-8 science classrooms and helps students relate physical changes to everyday life, environmental issues, and larger scientific principles.

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what-is-vapor-pressure-2 — Diagram of evaporation and condensation creating vapor pressure

Evaporation is the process that changes a liquid into a gas at the surface of the liquid. This transformation can happen at any temperature, not just when the liquid is boiling. Evaporation is a key part of the water cycle and affects many everyday situations, such as drying wet clothes or the disappearance of puddles after rain. Scientists study this process to understand how matter changes state and how energy interacts with substances.

How Evaporation Works

During evaporation, molecules at the surface of a liquid gain enough energy to break free from the liquid and enter the air as a vapor. This energy usually comes from heat. However, only molecules at the surface with enough energy escape, so evaporation is called surface-level vaporization. The process occurs at all temperatures, but it happens faster when the liquid is warmer, because more molecules have enough energy to leave. For example, after a summer rain, a puddle can dry up in a few hours thanks to high temperatures and sunlight providing energy for evaporation.

Factors That Affect Evaporation

Several factors interact to influence the rate of evaporation. Temperature is the most significant: the higher the temperature, the faster evaporation occurs. Surface area matters, too—a shallow pan of water will evaporate more quickly than the same amount of water in a tall glass because more molecules are exposed at the surface. Humidity in the air slows evaporation, since the air is already holding water vapor. Air movement, like wind, increases evaporation by moving moist air away from the surface, allowing more molecules to escape. For example, laundry dries faster on a breezy day than on a still, humid one. Research shows that on a hot, dry, and windy day, a small puddle can lose up to 80% of its water in just a few hours.

Evaporation in Everyday Life and the Environment

Evaporation has important effects beyond just drying things. In the water cycle, evaporation from lakes, rivers, and oceans moves water into the atmosphere, where it later forms clouds and precipitation. This process helps regulate Earth's climate and weather. Evaporation also cools surfaces, such as when sweat evaporates from skin, lowering body temperature. In technology, cooling towers in power plants rely on evaporation to remove excess heat. However, rapid evaporation in hot regions can lead to water shortages, affecting agriculture and communities.

Understanding evaporation helps us manage water resources and solve real-world problems. It connects to the larger scientific principle of the conservation of mass, since the water does not disappear—it changes form and moves through systems.

Interesting Fact:
Evaporation can occur even from ice at temperatures below freezing, a process called sublimation!

What is evaporation?

The process where a liquid changes into a gas at the surface.When a liquid boils and turns into a gas everywhere.The process where a solid turns into a liquid.Condensation of gas into a liquid.

Where does evaporation take place in a liquid?

At the surface of the liquid.At the bottom of the liquid.Throughout the whole liquid at once.Only inside a container.

According to the passage, which factor does NOT speed up evaporation?

High humidityHigh temperatureLarge surface areaWindy conditions

What happens to the molecules during evaporation?

They gain enough energy to escape into the air as vapor.They lose energy and freeze.They gather at the bottom of the container.They mix with solids to form new substances.

What is one real-world example of evaporation mentioned in the passage?

Puddles drying after rain.Ice melting in a freezer.Clouds forming in the sky.Metal rusting in air.

What does the term 'surface-level vaporization' mean in context?

Only molecules at the surface of the liquid turn into gas.The entire liquid boils at once.The process of turning solids directly into gas.Vapor forming under the surface of a solid.

Which best describes the relationship between temperature and evaporation?

Higher temperature increases evaporation rate.Lower temperature speeds up evaporation.Temperature does not affect evaporation.Evaporation only happens at freezing temperatures.

Why does air movement increase evaporation?

It removes moist air from the surface, allowing more molecules to escape.It cools down the liquid, making molecules move slower.It adds more water to the liquid.It blocks sunlight from reaching the liquid.

Evaporation can only happen when water is boiling. True or False?

TrueFalse

Evaporation is important in the water cycle. True or False?

TrueFalse