13.6 Humidity, Evaporation, and Boiling

Freeze drying is a process in which substances, such as foods, are dried by placing them in a vacuum chamber and lowering the atmospheric pressure around them. How does the lowered atmospheric pressure speed the drying process, and why does it cause the temperature of the food to drop?

Dry air is 78.1% nitrogen. What is the partial pressure of nitrogen when the atmospheric pressure is $1 . \text{01} \times \text{10}^{5} \text{ N}/\text{m}^{2}$?

Pressure cookers increase cooking speed by raising the boiling temperature of water above its value at atmospheric pressure. (a) What pressure is necessary to raise the boiling point to $\text{120} . 0 º \text{C}$? (b) What gauge pressure does this correspond to?

What is the atmospheric pressure on top of Mt. Everest on a day when water boils there at a temperature of $\text{70} . 0 º \text{C}?$

What is the relative humidity on a $\text{25} . 0 º \text{C}$ day when the air contains $\text{18} . 0 \text{ g}/\text{m}^{3}$ of water vapor?

A deep-sea diver should breathe a gas mixture that has the same oxygen partial pressure as at sea level, where dry air contains 20.9% oxygen and has a total pressure of $1 . \text{01} \times \text{10}^{5} \text{ N}/\text{m}^{2}$. (a) What is the partial pressure of oxygen at sea level? (b) If the diver breathes a gas mixture at a pressure of $2 . \text{00} \times \text{10}^{6} \text{ N}/\text{m}^{2}$, what percent oxygen should it be to have the same oxygen partial pressure as at sea level?

Air in human lungs has a temperature of $\text{37} . 0 º \text{C}$ and a saturation vapor density of $\text{44} . \text{0 g}/\text{m}^{3}$. (a) If 2.00 L of air is exhaled and very dry air inhaled, what is the maximum loss of water vapor by the person? (b) Calculate the partial pressure of water vapor having this density, and compare it with the vapor pressure of $6 . \text{31} \times \text{10}^{3} \text{ N}/\text{m}^{2}$.

Late on an autumn day, the relative humidity is 45.0% and the temperature is $\text{20} . 0 º \text{C}$. What will the relative humidity be that evening when the temperature has dropped to $\text{10} . 0 º \text{C}$, assuming constant water vapor density?

What is the dew point (the temperature at which 100% relative humidity would occur) on a day when relative humidity is 39.0% at a temperature of $\text{20} . 0 º \text{C}$?

The boiling point of water increases with depth because pressure increases with depth. At what depth will fresh water have a boiling point of $\text{150} º \text{C}$, if the surface of the water is at sea level?

To get an idea of the small effect that temperature has on Archimedes’ principle, calculate the fraction of a copper block’s weight that is supported by the buoyant force in $0 º \text{C}$ water and compare this fraction with the fraction supported in $\text{95} . 0 º \text{C}$ water.

(a) How many moles per cubic meter of an ideal gas are there at a pressure of $1 . \text{00} \times \text{10}^{\text{14}} \text{ N}/\text{m}^{2}$ and at $0 º \text{C}$? (b) What is unreasonable about this result? (c) Which premise or assumption is responsible?

The temperature inside a supernova explosion is said to be $2 . \text{00} \times \text{10}^{\text{13}} \text{ K}$. (a) What would the average velocity $v_{\text{rms}}$ of hydrogen atoms be? (b) What is unreasonable about this velocity? (c) Which premise or assumption is responsible?