Question

which statement(s) are true for a liquid that is at its boiling point?
select all that apply
a the molecules all throughout the liquid have enough kinetic energy to enter the gas phase.
b the vapor pressure of the liquid and the atmospheric pressure are equal.
c the temperature is 100°c or higher.
d the vapor pressure of the liquid is lower than the atmospheric pressure.

Explanation:

• Option a: At the boiling point, not all molecules have enough kinetic energy to enter the gas phase. Only those with sufficient energy (which is a fraction of the total molecules) can do so. So, this statement is false.
• Option b: By definition, the boiling point of a liquid is the temperature at which its vapor pressure equals the external (atmospheric) pressure. So, this statement is true.
• Option c: The boiling point of a liquid is not always \(100^{\circ}C\). For example, the boiling point of ethanol is \(78.37^{\circ}C\) at standard atmospheric pressure. The value of \(100^{\circ}C\) is the boiling point of water at standard atmospheric pressure. So, this statement is false.
• Option d: When the vapor pressure of the liquid is lower than the atmospheric pressure, the liquid will not boil. Boiling occurs when vapor pressure equals atmospheric pressure. So, this statement is false.

Answer:

B. The vapor pressure of the liquid and the atmospheric pressure are equal.