Passage IV

Four 1800s scientists provide different gas models that attempt to explain what happens when a gas is released into an evacuated container and what happens when a gas in a closed container of fixed volume is heated.

Scientist 1

A gas is composed of small particles that repel each other. The particles are bound together in a 3-dimensional lattice, but are never in contact with each other. If a gas is released into an evacuated container, the particles in the lattice will move apart from each other until the gas completely fills the container, then stop moving. Thus, the particles can move only if the size of their container changes.

If a gas in a closed container of fixed volume is heated, the repulsive forces between particles will increase. This cannot change the distance between the particles in the gas lattice, but does cause the lattice to push harder against the container, and thus increases the pressure.

Scientist 2

Scientist 1's model is correct with only one exception. If a gas in a closed container of fixed volume is heated, the repulsive force between particles will decrease, causing the gas lattice to push less hard against the container.

Scientist 3

A gas is composed of small particles that repel each other. The particles are not bound to each other and are in constant, random motion. If a gas is released into an evacuated container, the random motion will cause the gas to spread out to fill the container. If gas particles are on path to collide, the repulsive force between the particles will push each particle into a new path. Thus, gas particles never collide.

If a gas in a closed container of fixed volume is heated, the speed of the gas particles will increase. Therefore, the number of particles colliding with the walls of the container will increase, which will cause the pressure to increase. Increasing the temperature has no effect on the repulsive force.

Scientist 4

Scientist 3's model is correct, except that gas particles do not repel each other. (Nor do they attract each other.) Thus, gas particles can collide with each other. When they do collide, the collisions are elastic because no energy is lost during the collision.