What is boiling point?

What is boiling point?

• A. The temperature at which ignition occurs
• B. The temperature at which vapor pressure is zero
• C. The temperature at which vapor pressure of the liquid is equal to the external pressure applied to it.
• D. The temperature at which a liquid becomes a solid

Answer: (C)

Boiling point is the temperature at which the liquid’s vapor pressure becomes equal to the pressure exerted on it by the surroundings. When that balance is reached, bubbles of vapor form throughout the liquid, not just at the surface, and the liquid boils. Because vapor pressure increases with temperature, heating continues until it matches the external pressure, which is why the boiling point depends on how hard the surroundings push on the liquid. At standard atmospheric pressure around 1 atm, the boiling point is the temperature where the liquid’s vapor pressure reaches that 1 atm. If you raise the surrounding pressure, the boiling point goes up; if you lower it, the boiling point goes down. Ignition temperature is about the substance catching fire, not about transforming to a vapor phase. A vapor pressure of zero would mean no vapor forms at all, which isn’t the case for liquids. A liquid turning into a solid describes freezing, not boiling.

Boiling point is the temperature at which the liquid’s vapor pressure becomes equal to the pressure exerted on it by the surroundings. When that balance is reached, bubbles of vapor form throughout the liquid, not just at the surface, and the liquid boils. Because vapor pressure increases with temperature, heating continues until it matches the external pressure, which is why the boiling point depends on how hard the surroundings push on the liquid. At standard atmospheric pressure around 1 atm, the boiling point is the temperature where the liquid’s vapor pressure reaches that 1 atm. If you raise the surrounding pressure, the boiling point goes up; if you lower it, the boiling point goes down.

Ignition temperature is about the substance catching fire, not about transforming to a vapor phase. A vapor pressure of zero would mean no vapor forms at all, which isn’t the case for liquids. A liquid turning into a solid describes freezing, not boiling.