Question

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

Explanation:

• Option a: The boiling point of a liquid is specific to the substance and pressure. For example, water boils at \(100^{\circ}C\) at 1 - atm pressure, but other liquids like ethanol have lower boiling points (\(78.37^{\circ}C\) at 1 - atm). So, the statement "The temperature is \(100^{\circ}C\) or higher" is false in a general sense for any liquid at its boiling point.
• Option b: When a liquid is at its boiling point, the vapor pressure of the liquid is equal to the atmospheric pressure. If the vapor pressure were lower than the atmospheric pressure, the liquid would not boil. So, this statement is false.
• Option c: At the boiling point, the average kinetic energy of the molecules is sufficient for the phase change. Molecules throughout the liquid (not just on the surface as in evaporation) have enough kinetic energy to enter the gas phase. This statement is true.
• Option d: By the definition of the boiling point, the vapor pressure of the liquid \(P_{vapor}\) and the atmospheric pressure \(P_{atm}\) are equal (\(P_{vapor}=P_{atm}\)). This statement is true.

Answer:

C. The molecules all throughout the liquid have enough kinetic energy to enter the gas phase; D. The vapor pressure of the liquid and the atmospheric pressure are equal.