Question

Hikers were climbing Mount McKinley and pitched camp part way up. While boiling eggs in water for breakfast, they noticed that the temperature of the boiling water was 79.0 °C. What was the atmospheric pressure (in torr) at their elevation? (The ∆Hvap of water is 40.7 kJ/mol).1

Answer 1

We know that the boiling temperature of the water depends on the atmospheric pressure.

Here we will find that the atmospheric pressure is 760.62 torr.

To get the atmospheric pressure we need to analyze the given information.

Boiling temperature = 79.0°C

∆Hvap = 40.7 kJ/mol

The equation we need to use is:

$ln(p_1/p_2) = \frac{\Delta H}{n*R} (\frac{1}{T_1} - \frac{1}{T_2} )$

Where:

p₁ = 1 atm

p₂ = what we want to know.

n*R = 8.314 J/K*mol

T₁ = (100° + 273.15°) = 374.15°

T₂ = (79.0  + 273.15°) = 352.15°K

We can replace all that in the equation to get:

$ln(1 atm/p_2) = \frac{40.7 kJ/mol}{8.314 J/K*mol} (\frac{1}{374.15\°K} - \frac{1}{352.15\°K} ) = -0.000817\\\\p_2 = (1atm)/exp(-0.000817) = 1.000817 atm$

And we want this in torr:

1 atm = 760 torr.

Then 1.000817 atm = 760.62 torr.

This is the pressure at the mountain.

if you want to learn more, you can read:

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