How is it possible that a substance like liquid nitrogen can boil even though it is very cold?

• A. Boiling occurs when the vapor pressure of the liquid equals the external pressure, regardless of the absolute temperature.
• B. Boiling only happens when a substance reaches room temperature.
• C. Boiling is caused by chemical reactions that occur at low temperatures.
• D. Liquid nitrogen boils because it absorbs heat and becomes warmer than its surroundings.

Answer: (A)

Verified step by step guidance

1. Understand the concept of boiling: boiling occurs when the vapor pressure of a liquid equals the external (atmospheric) pressure.
2. Recognize that vapor pressure depends on temperature, but boiling can happen at any temperature if the vapor pressure matches the external pressure.
3. Apply this to liquid nitrogen: even though it is very cold, it has a vapor pressure that reaches atmospheric pressure at its boiling point (around -196°C), causing it to boil.
4. Note that boiling is a physical change related to pressure and temperature, not necessarily to the liquid reaching room temperature or undergoing chemical reactions.
5. Conclude that liquid nitrogen boils because it absorbs heat from the surroundings, increasing its vapor pressure until it equals the external pressure, allowing bubbles of vapor to form and the liquid to boil.