Boiling requires the addition of heat.

• A. False
• B. Depends on the substance
• C. It is not required
• D. Only at high altitude

Answer: (A)

Boiling is determined by the liquid’s vapor pressure reaching the surrounding pressure, not simply by adding heat. You raise the temperature to the boiling point under a given pressure to supply the latent heat needed for the phase change, but you can also make a liquid boil by lowering the ambient pressure below its vapor pressure at its current temperature. For example, in a vacuum, water can begin to boil at room temperature because the pressure is low enough for its vapor pressure to exceed it. So the act of boiling does not inherently require heat input at all times; heat is typically involved when you want to drive the temperature up to the boiling point or sustain the phase change, but it’s not a universal prerequisite for boiling to begin.