Question

Explain each of the following observations: a. Boiling water at sea level is hotter than boiling water in the mountains. b. Water used to sterilize surgical equipment is heated to \(120^{\circ} \mathrm{C}\) at \(2.0 \mathrm{~atm}\) in an autoclave.

Short answer

a. Higher atmospheric pressure at sea level increases boiling temperature. b. Elevated pressure in an autoclave raises boiling point to 120°C for sterilization.

Step-by-step solution

Understanding Boiling Point and Altitude

Boiling point is the temperature at which a liquid's vapor pressure equals the external pressure. At lower altitudes (sea level), atmospheric pressure is higher than at higher altitudes (mountains).

Boiling Water at Sea Level vs. Mountains

At sea level, the atmospheric pressure is higher, requiring water to reach a higher temperature (100°C) for its vapor pressure to equal the atmospheric pressure and boil. In the mountains, the atmospheric pressure is lower, so water boils at a lower temperature because it reaches equilibrium vapor pressure at a lower temperature.

Sterilization in an Autoclave

Autoclaves use higher pressures (2.0 atm) to increase the boiling point of water. When the pressure is increased from 1 atm to 2 atm, the boiling point of water also increases, allowing it to reach 120°C. This higher temperature is effective for sterilizing surgical equipment by killing bacteria and other microorganisms.

Summary

a. Water boils at a higher temperature at sea level due to higher atmospheric pressure. b. An autoclave uses elevated pressure to increase the boiling point of water to 120°C for effective sterilization.

Key concepts

boiling point

When we talk about the boiling point of a liquid, we are referring to the temperature at which the liquid's vapor pressure equals the external pressure surrounding the liquid. This means that at the boiling point, molecules within the liquid have enough energy to transition into the gas phase. The boiling point of water, for example, changes based on the atmospheric pressure around it.
At sea level, the atmospheric pressure is standard, which is why water boils at 100°C. However, if you were to climb a mountain, the atmospheric pressure decreases because there is less air overhead. Therefore, water will boil at a lower temperature in high-altitude areas because it takes less heat for the water vapor pressure to match the lower atmospheric pressure.

atmospheric pressure

Atmospheric pressure is the force exerted by the weight of the air above us. This pressure varies depending on altitude. At sea level, atmospheric pressure is about 1 atmosphere (atm), which is ideal for many everyday processes, including boiling water. As you go higher in altitude, such as in the mountains, atmospheric pressure decreases, making it easier for water to boil but at a lower temperature.
Understanding atmospheric pressure is crucial for many scientific applications. For instance, in cooking, you might find that food cooks differently at higher elevations because water boils at a lower temperature. This concept also plays a significant role in medical applications, like autoclave sterilization, which relies on increased pressures to achieve higher boiling points.

autoclave sterilization

Autoclaves are specialized devices used primarily for sterilizing medical and laboratory equipment. They work by increasing the pressure within a sealed chamber, which subsequently raises the boiling point of water used for sterilization.
For example, in an autoclave set to 2 atmospheres of pressure, the boiling point of water increases to about 120°C instead of the usual 100°C at standard atmospheric pressure. This higher temperature is crucial for effectively sterilizing surgical equipment. At 120°C, the heat is enough to kill bacteria, viruses, and spores that are otherwise resistant to lower temperatures.
Autoclave sterilization is a reliable method because it ensures that all parts of the equipment get exposed to the elevated temperature for a sufficient time, ensuring thorough sterilization.

vapor pressure equilibrium

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature. The concept of vapor pressure equilibrium is critical for understanding boiling points as it describes the point where the number of molecules entering the vapor phase equals the number returning to the liquid.
When heating a liquid, such as water, its vapor pressure increases until it reaches the same level as the external pressure. At this point, the liquid boils. Therefore, in an environment with lower atmospheric pressure, the vapor pressure equilibrium is achieved at a lower temperature, leading to a lower boiling point.
Similarly, in an autoclave, the pressure inside is increased, raising the temperature at which water reaches vapor pressure equilibrium. This method ensures a higher boiling point, which is useful for applications requiring sterilization.