What Is Vapor Pressure?

About this printable What Is Vapor Pressure science reading passage, NGSS-aligned (Grades 5-8)

This NGSS-aligned science passage explains the concept of vapor pressure in an age-appropriate, engaging way for middle school students. It introduces how vapor pressure forms when molecules of a liquid evaporate and exert pressure in a closed system. The passage covers how different liquids have different vapor pressures and how temperature influences evaporation and boiling. Real-world examples, like alcohol evaporating faster than water and water boiling at different temperatures at varying altitudes, help students understand key concepts. It also explores how vapor pressure plays a critical role in boiling and connects to air pressure. The passage aligns with MS-PS1-4 under Physical Science, helping students interpret and explain scientific phenomena related to states of matter and energy. This resource is ideal for science reading comprehension practice and supports understanding of core NGSS concepts.

Written by Neha Goel TripathiPublished by Workybooks

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Sample passage and quiz from What Is Vapor Pressure

Have you ever seen water slowly disappear from a cup left out for days? That’s not magic—it’s science! Even without boiling, water can turn into vapor. This process is called evaporation, and it's closely linked to something called vapor pressure.

Vapor pressure is the pressure caused by a liquid's vapor when the liquid and gas are in balance. When a liquid evaporates, its molecules escape into the air. These gas molecules bump into things around them, creating pressure. The more molecules that evaporate, the higher the vapor pressure becomes. If a liquid is in a closed container, the vapor collects above the liquid, and the pressure it causes is the vapor pressure.

Different liquids have different vapor pressures. For example, alcohol has a higher vapor pressure than water at the same temperature. That means alcohol evaporates faster. Liquids with high vapor pressure are usually more "volatile," meaning they change into gas easily. Temperature affects vapor pressure too. As heat increases, molecules move faster and more of them escape into gas form—so vapor pressure rises.

Vapor pressure also helps explain how boiling works. A liquid boils when its vapor pressure equals the air pressure around it. At sea level, water boils at 100°C (212°F) because its vapor pressure matches the outside air pressure at that temperature. But on a mountain, where the air pressure is lower, water boils at a lower temperature.

Fun Fact: In space, where there’s almost no air pressure, your sweat would boil right off your skin—even at body temperature!