Name: vapor pressure and boiling behavior
Uploaded: 2025-02-13T15:43:08.000Z
Duration: 1 min 28 s
Channel: JoVE

The vapor pressure, which influences boiling and cavitation, is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature and indicates the tendency of molecules to escape from the liquid surface.
In a closed, evacuated container, liquid molecules escape into space, raising the pressure until equilibrium is achieved, where the rate of molecules escaping equals the rate of returning. This equilibrium pressure is the vapor pressure.
Vapor pressure depends on temperature. As temperature rises, molecules gain kinetic energy, overcoming intermolecular forces and escaping into the vapor phase more easily, which increases vapor pressure.
For example, water at 100&#176;C has a vapor pressure of 101.3 kPa,&#160; which matches atmospheric pressure at sea level, causing it to boil. At higher altitudes, with lower atmospheric pressure, water boils at lower temperatures because its vapor pressure matches the reduced atmospheric pressure more quickly.
Monitoring vapor pressure is crucial in designing and operating pumps and turbines to prevent cavitation.
Cavitation occurs when local fluid pressure drops below the vapor pressure, forming vapor bubbles that collapse violently, damaging equipment.

vapor pressure of fluid

The vapor pressure of a fluid is a crucial concept in fluid mechanics, influencing phenomena such as boiling and cavitation. Vapor pressure refers to the pressure exerted by a vapor at a state of thermodynamic equilibrium with its corresponding liquid phase at a specific temperature. It represents the tendency of molecules to escape from the fluid surface into the vapor phase.
When a liquid is placed in a closed container with a small air space, and the space is evacuated, vapor molecules will escape from the liquid into the space. As more molecules escape, the pressure in the space increases until an equilibrium is reached, where the rate of molecules escaping the liquid equals the rate of molecules returning to it. This equilibrium pressure is the vapor pressure of the liquid.
Vapor pressure is temperature-dependent. As the temperature increases, the molecules&#39; kinetic energy increases, resulting in more molecules overcoming intermolecular forces and escaping into the vapor phase. It follows that the vapor pressure increases with temperature. For instance, water at 100&#176;C has a vapor pressure of 101.3 kPa (1 atm), allowing it to boil at standard atmospheric pressure. However, at higher elevations, where atmospheric pressure is lower, water boils at lower temperatures because its vapor pressure equals the reduced atmospheric pressure at the higher elevation.

Vapor Pressure of Fluid

The vapor pressure, which influences boiling and cavitation, is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature and ...

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Fluid Properties

KEY TERMS AND CONCEPTS

vapor pressure and boiling behavior

Vapor pressure and boiling behavior are closely linked in fluids. Vapor pressure is the pressure a vapor exerts when it is in thermodynamic equilibrium with its liquid at a given temperature. It shows how strongly molecules tend to leave the liquid surface and move into the vapor phase.

A closed container helps show how vapor pressure forms. If a liquid sits in a sealed space with a small air gap, and that space is evacuated, vapor molecules escape from the liquid into the empty space. The pressure rises as more molecules collect there. Soon, the rate of molecules leaving the liquid equals the rate returning to it. That balance creates the vapor pressure of the liquid.

Temperature changes vapor pressure. When temperature increases, the molecules gain kinetic energy. More molecules can overcome intermolecular forces and escape into the vapor phase. For that reason, vapor pressure increases as temperature increases.

Water gives a clear example. At 100°C, water has a vapor pressure of 101.3 kPa, or 1 atm. That is why it can boil at standard atmospheric pressure. At higher elevations, atmospheric pressure is lower. Water then boils at a lower temperature because its vapor pressure reaches the reduced outside pressure sooner.

Vapor Pressure and Boiling Behavior

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Vapor pressure and boiling behavior are closely linked in fluids. Vapor pressure is the pressure a vapor exerts when it is in thermodynamic equilibrium with its liquid at a given temperature. It shows how strongly molecules tend to leave the liquid surface and move into the vapor phase. A closed container helps show how vapor pressure forms. If a liquid sits in a sealed space with a small air gap, and that space is evacuated, vapor molecules escape from the liquid into the empty space. The...

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key terms and concepts

Learn how vapor pressure forms, why it rises with temperature, and how it explains boiling in water at sea level and higher elevations.

Vapor Pressure and Boiling Behavior | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

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Vapor Pressure and Boiling Behavior

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