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Lesson 8 - Understanding Atmospheric Pressure - Page 3 |
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Effects of Barometric Pressure on Vapor Pressure Atmospheric pressure can also alter a liquid's boiling point. When a liquid is heated, molecules escape from the surface into the atmosphere. The pressure of this vapor is called the liquid's vapor pressure. When the vapor pressure equals the pressure of the atmosphere bearing down on the surface of the liquid, the liquid boils. As altitude increases, atmospheric pressure decreases, so a liquid requires less energy for the molecules to reach escape velocity and boils at lower temperatures. |
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Effects of Barometric Pressure on Vapor Pressure
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Questions for Consideration: Q. What environmental exists where the atmospheric pressure is extremely low--perhaps there are no air molecules at all? Q.What would happen to a pan of water in such a zero atmospheric pressure? Q.What would happen to the liquids in a human body if the atmospheric pressure registered zero?
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History Notes The first known barometer was made by a scientist named Evangelisto Torricelli. Attempting to measure air pressure, Torricelli came up with the idea of using sealed tubes in a pan of mercury to see if the force from the air could move the mercury up into the tube. It worked, and eventually Torricelli could determine that atmospheric pressure will typically support a column of mercury about 30 inches (76 centimeters) high. Today meteorologists still use that measurement as the standard atmospheric pressure at sea level. |
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