At high altitudes, the boiling point of water decreases because?

KPSC Staff Nurse - 2016

General Knowledge

Medium

Appeared in: KPSC Staff Nurse - 2016

Explanation

The boiling point is defined as the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure.
At higher altitudes, the atmospheric pressure is lower because there is less air in the column above, as stated in physics principles.
Therefore, less heat energy is required to bring the water's vapor pressure to this lower atmospheric pressure, causing it to boil at a temperature below the standard 100°C.

Option A: High atmospheric pressure increases, not decreases, the boiling point. More energy is required to overcome the greater external pressure.
Option B: The ambient (surrounding) temperature does not determine the boiling point. The boiling point is a physical property dependent on pressure.
Option D: Similar to the 'low temperature' option, the ambient temperature does not set the boiling point. The relationship is between the liquid's temperature and the external pressure.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Relationship between atmospheric pressure, altitude, and boiling point as background academic context rather than a clinical decision trigger.
The principle of pressure affecting boiling point is critical for understanding sterilization with an autoclave. Nurses must verify that the autoclave has reached the correct pressure (e.g., 15 psi) to ensure the steam temperature reaches 121°C for effective sterilization.
This knowledge is also relevant for patient education, for example, explaining to a patient on home oxygen why their humidifier might behave differently if they travel to a high-altitude location.
What if an autoclave cycle fails to reach the target pressure? If the pressure remains low, the steam temperature will not reach 121°C. This results in incomplete sterilization, creating a high risk of healthcare-associated infections (HAIs) from contaminated instruments.

How to Approach the Question

Identify the core scientific concept: The question asks for the reason behind a change in the boiling point of water.
Recall the definition of boiling point: It's the temperature where a liquid's vapor pressure equals the external atmospheric pressure.
Analyze the relationship between the variables mentioned: 'high altitude' and 'atmospheric pressure'. Remember that as altitude increases, atmospheric pressure decreases.
Synthesize the concepts: If atmospheric pressure is lower at high altitudes, then the temperature required for the vapor pressure to match it must also be lower.
Evaluate the options based on this logical deduction. The option 'The atmospheric pressure is low' directly provides the cause for the decreased boiling point.

Concept Tested & Keywords

Concept Tested: Relationship between atmospheric pressure, altitude, and boiling point.
Stem keywords: high altitudes, boiling point, water, decreases
Lead-in keywords: because
Negative lead-in flag: false

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 63-65