At higher altitudes, there is lower atmospheric pressure and the boiling point ________.

At higher altitudes, there is lower atmospheric pressure and the boiling point ________.

• A. fluctuates
• B. decreases
• C. stays the same
• D. increases

Answer: (B)

Boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding atmospheric pressure. At higher altitudes the air pressure is lower, so the vapor pressure needed to overcome that external pressure is reached at a lower temperature. In other words, less heat is required for the liquid to start boiling when the surrounding pressure is reduced, so the boiling point decreases. For example, water boils at 100°C at sea level, but at higher elevations it boils at temperatures well below that. This is why the boiling point decreases as altitude increases. It does not stay the same or increase with lower pressure, and it isn’t a matter of fluctuation.

Boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding atmospheric pressure. At higher altitudes the air pressure is lower, so the vapor pressure needed to overcome that external pressure is reached at a lower temperature. In other words, less heat is required for the liquid to start boiling when the surrounding pressure is reduced, so the boiling point decreases. For example, water boils at 100°C at sea level, but at higher elevations it boils at temperatures well below that. This is why the boiling point decreases as altitude increases. It does not stay the same or increase with lower pressure, and it isn’t a matter of fluctuation.