Vapor Pressure The vapor pressure of a substance describes how readily molecules

Question

Vapor Pressure The vapor pressure of a substance describes how readily molecules at the surface of the substance enter the gaseous phase. At the boiling point of a liquid, the liquid's vapor pressure is equal to or greater than the atmospheric pressure exerted on the surface of the liquid. Since the atmospheric pressure at higher elevations is lower than at sea level, the boiling point of water decreases as the elevation increases. The atmospheric pressure at sea level is 760 mmHg. This pressure decreases by 19.8 mmHg for every 1000-ft increase in elevation. Elevation Pressure 0 ft 760 mmHg 1000 ft 740.2 mmHg 2000 ft 720.4 mmHg The boiling point of water decreases 0.05C for every 1 mmHg drop in atmospheric pressure.

What is the boiling point of water at an elevation of 1.00×104 ft ? Express your answer with the appropriate units using three significant figures.

Explanation / Answer

For every 1000 ft, the pressure decrease by 19.8 mm Hg

Pressure at an elevation of 10000 ft = 760 - 19.8 * 10 = 760 - 198 = 562 mm Hg

The difference in pressure = 198 mm Hg

For ever 1mm Hg drop in pressure, boiling point decreases by 0.05C

Decrease in boiling point = 198 mm Hg * 0.05C/mm Hg = 9.9C

Boiling Point of water = 100C - 9.9C = 91.1 C

Hence the correct answer with three significant digits is equal to 91.1C

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