Question

At higher altitudes the boiling point of water lowers because (1) atmospheric pressure is low (2) temperature is low (3) atmospheric pressure is high (4) none of these

Short answer

The boiling point of water lowers because atmospheric pressure is low (Option 1).

Step-by-step solution

Understanding the Boiling Point

The boiling point of water decreases as the atmospheric pressure decreases. This is because boiling happens when the vapor pressure of the liquid equals the atmospheric pressure.

High Altitudes and Atmospheric Pressure

At higher altitudes, the atmospheric pressure is lower compared to sea level. This means that water will boil at a lower temperature because it reaches the vapor pressure needed to boil more quickly.

Eliminating Incorrect Options

Since the boiling point of water is directly related to atmospheric pressure, options (2) and (3) are incorrect because they either mention low temperature or high atmospheric pressure. Option (4) is incorrect because there is a correct reason.

Identifying the Correct Answer

Given that the correct reasoning is the atmospheric pressure being low, option (1) is the correct answer.

Key concepts

headline of the respective core concept

One fundamental idea profoundly impacting the boiling point of liquids, especially water, is the concept of atmospheric pressure. Atmospheric pressure is the force exerted onto a surface by the weight of the air above that surface. It varies with altitude, weather conditions, and temperature. At sea level, the atmospheric pressure typically is 1 atm (101.3 kPa). This pressure decreases as one goes up in altitude because there is less air overhead to exert force.Lower atmospheric pressure at high altitudes means that the air is 'thinner'. This thin air exerts less pressure on the surface of the water. As a result, the water molecules require less energy to escape into the air and form vapor. This lower energy threshold lowers the boiling point of water. In essence, at higher altitudes, the atmospheric pressure is insufficient to hold the water molecules tightly, causing them to turn into gas at lower temperatures. Therefore, understanding the atmospheric pressure is key to grasping why water boils at lower temperatures in elevated regions.

headline of the respective core concept

Vapor pressure is key in determining when a liquid will boil. It is the pressure exerted by the vapor when it is in equilibrium with its liquid phase. Boiling occurs when the vapor pressure equals atmospheric pressure. At higher altitudes, atmospheric pressure is low. This means the vapor pressure needed for water to boil is achieved at a lower temperature. In simple terms, vapor pressure is like the strength of water molecules escaping into the air. When these escaping molecules push as hard against the air as the air pushes back (atmospheric pressure), the liquid begins to boil. So, when you climb up a mountain, the air pushes back less, allowing water to boil at a lower temperature. This reduction in boiling point with altitude is a clear effect of vapor pressure being able to reach equilibrium with the atmospheric pressure sooner.

headline of the respective core concept

Boiling point depression at high altitudes can be understood by combining the concepts of atmospheric pressure and vapor pressure. The term 'boiling point depression' describes the phenomenon where the boiling point of a liquid is reduced when the atmospheric pressure is lower. Simply put, in the mountains or high-altitude areas, cooking and boiling take place at lower temperatures. Unlike freezing point depression, where solutes lower freezing points, boiling point depression deals mainly with atmospheric variations. At sea level, water boils at 100°C, but in elevated areas, it could boil at 90°C or even lower. Some key points to remember:

• Lower atmospheric pressure means lower boiling point.
• Water molecules need less energy to escape into vapor.
• Boiling point depression affects cooking times and processes in high-altitude regions.

This knowledge is crucial for adjusting recipes and understanding natural processes at different altitudes.