What is the term for the temperature at which a liquid changes to a gas?

• A. Boiling point
• B. Freezing point
• C. Melting point
• D. Condensation point

Answer: (A)

Boiling point is the temperature at which a liquid changes into a gas. At this temperature the liquid’s vapor pressure equals the surrounding pressure, so bubbles of vapor form inside the liquid and rise to the surface. Below this temperature, evaporation can occur at the surface, but the liquid doesn’t boil throughout. The boiling point depends on pressure: higher external pressure raises it, lower pressure lowers it. For pure water at 1 atmosphere, the boiling point is 100°C. The other terms describe different phase changes (freezing/melting solidify or melt, condensation is gas to liquid).