7. What assumption of the kinetic-molecular theory explains why a gas can expand to fill a container?

Gas molecules move at random with no attractive forces between them.

Explanation:

Kinetic-molecular theory is based on the following postulates, or assumptions.

Gases are composed of a large number of particles that behave like hard, spherical objects in a state of constant, random motion.

These particles move in a straight line until they collide with another particle or the walls of the container.

These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.

There is no force of attraction between gas particles or between the particles and the walls of the container.

Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.

The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.