Question

A liquid is in equilibrium with its vapor at its boiling point. On the average, the molecules in the two phases have equal:
A.Intermolecular forces
B.Potential energy
C.Total energy
D.Kinetic energy

Answer 1

Hint: Bubbles of vapour form inside the liquid at the boiling point and float to the surface. A liquid's boiling point varies according to the pressure applied.

Complete step by step answer:
Let’s first learn about boiling point and its properties;
The boiling point is the temperature at which the pressure imposed by the atmosphere on a liquid is equal to the pressure imposed by the liquid vapor. The addition of heat results in the conversion of the liquid into its vapour without increasing the temperature under this condition.
Now, regarding the question, there is a theory named “kinetic theory of gases”;
The kinetic theory of gases is a theory based on the simplified definition of a gas by molecule or atom, from which certain gas properties can be obtained.
According to this theory average kinetic energy of gas molecules are directly proportional to the absolute temperature of the system;
$\,(\varepsilon ) = \dfrac{3}{2}{k_B}T\,$
Where, $\,T\,$is the absolute temperature, $\,{k_B}\,$ is the boltzmann constant, $\,\varepsilon \,$ is the average kinetic energy.
Kinetic energy is thus directly related to temperature. As the liquid is in equilibrium with its vapor at the boiling point, the temperatures are the same. So, the molecules in two different phases have the same kinetic energy as at the same temperature.
While looking into the other options, we can see that the intermolecular forces are different at two phases even if they are in equilibrium. Potential energy and total energy are also different.
So, for this question option D is the correct answer.


Note:
The kinetic theory model represents a perfect gas and, especially at the limit of extreme dilution and high temperature, is a realistic approximation to a real gas. However, such a simplistic definition is not sufficiently accurate to account for the high-density behaviour of gases.