Kinetic Molecular Theory

The Kinetic Molecular Theory Gases consist of tiny particles (atoms or molecules). These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero).

The Kinetic Molecular Theory The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. The particles are assumed not to attract or to repel each other. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

The Kinetic Molecular Theory Click here to watch the animation. The animation shows the different movement of molecules in solid, a liquid, and a gas. The animation is a model. A model is a simplified approximation of reality.

Implications of The Kinetic Molecular Theory with respect to TEMPERATURE The temperature is directly proportional to the degree of motion of the particles in a substance. The temperature of a gas reflects how rapidly the individual particles are moving.

Implications of The Kinetic Molecular Theory with respect to TEMPERATURE At HIGH temperatures, the particles move very fast and hit the walls of the container frequently. At LOW temperatures, the particles move slowly and hit the walls of the container not as often.

Implications of The Kinetic Molecular Theory with respect to TEMPERATURE and PRESSURE Picture a rigid container – as the gas in the container is heated to a higher temperature, the particles move faster, hitting the walls more often. These impacts become more forceful as the particles move faster. Pressure is due to the collisions with the walls of the container. So as the temperature increases, the gas pressure also increases. Pressure is directly proportional to temperature.

Implications of The Kinetic Molecular Theory with respect to TEMPERATURE and VOLUME Picture a container with a movable lid with constant pressure – As the temperature increases, the particles move faster, causing the gas pressure to increase. Thus the volume of the gas will increase as we raise its temperature. Volume is directly proportional to temperature.

Real Gases So far, we have assumed that we are dealing with an ideal gas. Of course, there is no such thing as an ideal gas! But… real gases behave like ideal gases under many conditions.

Real Gases Real gases behave differently than ideal gases under conditions of HIGH pressure (small volume) and LOW temperatures. We typically deal with gases that have pressures near 1 atm, so we can safely assume ideal gas behavior in all of our calculations.