Problem 5 - Chemistry for Allied Health

Question

Describe the relationship between boiling point and altitude.

Step-by-Step Solution

Answer

The boiling point decreases as altitude increases because atmospheric pressure is lower at higher altitudes.

Step 1: Define Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. At this point, the liquid turns into vapor.

Step 2: Understand Atmospheric Pressure Variation with Altitude

As altitude increases, atmospheric pressure decreases. This is because the higher you go above sea level, the less air there is above you, leading to decreased pressure.

Step 3: Relate Boiling Point to Atmospheric Pressure

Since the boiling point is where the vapor pressure of a liquid equals atmospheric pressure, a decrease in atmospheric pressure at higher altitudes means the boiling point is reached at a lower temperature.

Step 4: Apply the Concept

At sea level, atmospheric pressure is higher, so the boiling point of water is 100°C (212°F). At higher altitudes, such as in mountainous areas, the boiling point of water drops below 100°C due to the decreased atmospheric pressure.

Key Concepts

Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of the air above a given point on Earth. Imagine it as a blanket of air that is denser closer to the ground and thins out as you move higher up into the sky.

• At sea level, atmospheric pressure is at its highest because there is an entire column of air pressing down from above.
• As you ascend to higher altitudes, less air is present above, reducing the weight pressing down on you, and therefore, reducing atmospheric pressure.

You can think of it like a thick crowd at the base of a mountain thinning out the higher you climb.

Vapor Pressure

Vapor pressure is the pressure exerted by the vapor evaporating from a liquid's surface back into a gaseous state. This is a natural process that occurs as some molecules in a liquid with enough energy escape into the air, contributing to this vapor pressure above the liquid.

• A liquid will have a higher vapor pressure at higher temperatures as more molecules have the necessary energy to escape.
• In a closed system, vapor pressure will increase as more liquid transitions to a gaseous form, until it reaches equilibrium.

Vapor pressure is like the steam that rises from a hot cup of coffee, hinting at how ready your drink's molecules are to leave their liquid form.

Boiling Point

The boiling point of a liquid isn’t just about reaching a specific temperature. It's when the vapor pressure equals atmospheric pressure, allowing the liquid to transition entirely into vapor.

• At sea level, where atmospheric pressure is typically 101.3 kPa, water boils at 100°C (212°F).
• When vapor pressure is strong enough to overcome atmospheric pressure, bubbles form within the liquid, leading to boiling.

Imagine the bubbling pot of water on your stove – that's a battle between vapor pressure and atmospheric pressure won by the former!

Altitude Effect

The effect of altitude profoundly influences boiling points, primarily because higher altitudes mean lower atmospheric pressure. As a result:

• At lower atmospheric pressures found at high altitudes, the boiling point of a liquid is reduced.
• This means, for example, in mountainous regions, water can boil at temperatures significantly below 100°C.

Consider a mountaintop, where cooking times might be longer because boiling is achieved at lower, less intense temperatures. It's as if the boiling pot has less fuel for the fire, transforming liquid to gas more gently.