The process whereby a liquid turns spontaneously into vapour is called

1. Analyze the question

The question asks for the specific term used to describe the spontaneous change of a substance from a liquid state to a gaseous (vapour) state.

2. Explain the concept

• Evaporation: This is a surface phenomenon where liquid molecules gain enough kinetic energy to escape into the atmosphere as vapour. It occurs at any temperature below the boiling point and happens spontaneously at the surface of the liquid.
• Boiling: This is a bulk phenomenon where the entire liquid turns into vapour at a specific temperature called the boiling point. It requires an external heat source to maintain the process.
• Regelation: This is the phenomenon where ice melts under pressure and refreezes when the pressure is removed.
• Sublimation: This is the process where a solid changes directly into a gas without passing through the liquid state (e.g., camphor or dry ice).

3. Show the solution

• Since the question specifies a spontaneous process where a liquid turns into vapour, we must look for the term that describes a natural, surface-level transition.
• Boiling is not spontaneous in the same sense because it requires the liquid to reach its specific boiling point through added heat.
• Evaporation happens naturally at the surface of a liquid at any temperature, making it the correct definition for the process described.

4. Identify the answer

Comparing our analysis to the options provided:

• A. regelation (Incorrect)
• B. evaporation (Correct)
• C. boiling (Incorrect - requires specific temperature/heat)
• D. sublimation (Incorrect - involves solids)

5. Tip

To remember the difference: Evaporation happens at the surface and at any temperature (think of a puddle drying up on a sunny day), while Boiling happens throughout the entire liquid and only at a fixed temperature (think of water in a kettle).