Question

What is the boiling point of water at an elevation of 5000 ft ? Express your answer with the appropriate units using three significant figures.

Constants | Periodic Table

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 0.05∘C for every 1 mmHg drop in atmospheric pressure.

Answer 1

It is given that the pressure drop for every 1000 feet increase in elevation  is 19.8 mm Hg.

The pressure drop at an elevation of 5000 feet = 5 x 19.8 mm Hg = 99 mm Hg ( Atmospheric Pressure at an elevation of 5000 feet = 760mmHg-99mmHg =661mmHg)

The boiling point of water decreases by 0.05 C for every 1mmHg drop in atmospheric pressure.

The decrease in boiling point for a pressure drop of 99 mm Hg = 99 x 0.05 C = 4.95 C

Boiling point of water at a pressure of 760 mm Hg = 100 C

Boiling point of water at an elevation of 5000 feet ,where the atmospheri pressure is 661 mmHg = 100C - 4.95 C = 95.05 C