States of Matter Chapter 13

GASES Section 13.1

Kinetic-Molecular Theory Objects in motion have energy called kinetic energy. The kinetic-molecular theory describes the behavior of gases in terms of particles in motion. The model makes several assumptions about the size, motion, and energy of gas particles.

Particle Size Gases consist of small particles that are separated from one another by empty space. The volume of the particles is small compared with the volume of the empty space. Because gas particles are far apart, there are no significant attractive or repulsive forces among them.

Particle Motion Gas particles are in constant, random motion. Particles move in a straight line until they collide with other particles or with the walls of their container. Collisions between gas particles are elastic. An elastic collision is one in which no kinetic energy is lost. Kinetic energy may be transferred between colliding particles, but the total kinetic energy of the two particles does not change.

Particle Energy

Explaining the Behavior of Gases Kinetic-molecular theory can help explain the behavior of gases. For example, the constant motion of gas particles allows a gas to expand until it fills its container. What property of gases makes it possible for an air-filled flotation device to work?

Low Density – Density is mass per volume – A great deal of space exists between gas particles Compression and Expansion – Gases expand until they fill their container Diffusion and Effusion – Diffusion is the term used to describe the movement of one material through another from high to low concentration. – During effusion, a gas escapes through a tiny opening. – Graham’s law of effusion states that the rate of effusion for a gas is inversely