Which term is the temperature at which a substance changes from a liquid to a gas?

Which term is the temperature at which a substance changes from a liquid to a gas?

• A. Freezing point
• B. Boiling point
• C. Melting point
• D. Absolute zero

Answer: (B)

When a liquid changes into a gas, the temperature at which this happens is called the boiling point. This occurs when the liquid’s vapor pressure rises to reach the surrounding pressure, so enough energy is available to overcome intermolecular forces throughout the liquid and create vapor bubbles. At standard atmospheric pressure, for example, water boils at 100°C, but the exact boiling point depends on the external pressure. This is different from the freezing point, which is the temperature at which a liquid becomes a solid, and from the melting point, which is the temperature at which a solid becomes a liquid. Absolute zero is the lowest possible temperature, 0 Kelvin, where molecular motion is minimal.

When a liquid changes into a gas, the temperature at which this happens is called the boiling point. This occurs when the liquid’s vapor pressure rises to reach the surrounding pressure, so enough energy is available to overcome intermolecular forces throughout the liquid and create vapor bubbles. At standard atmospheric pressure, for example, water boils at 100°C, but the exact boiling point depends on the external pressure.

This is different from the freezing point, which is the temperature at which a liquid becomes a solid, and from the melting point, which is the temperature at which a solid becomes a liquid. Absolute zero is the lowest possible temperature, 0 Kelvin, where molecular motion is minimal.