Chapter 10 Notes Kinetic Theory in Solids, Liquids and Gases

Kinetic Theory Kinetic Energy—Energy that an object has due to motion. The Kinetic Theory is that tiny particles form all matter, and they are constantly in motion.

Kinetic Theory and Gases 1)A gas is composed of particles that are small, hard spheres with insignificant volume and no particle interaction.

Kinetic Theory and Gases 2)Particles in a gas are in constant motion—they travel straight paths unless they collide with another particle or their container.

Kinetic Theory and Gases 3)All collisions are considered elastic—no energy is lost to friction.

Gas Pressure Kinetic theory explains the existence of gas pressure. Gas pressure—the force exerted by a gas per unit surface area.

Gas Pressure The force of one molecule hitting an object is relatively small, but the result of billions of particles of air hitting a surface at once is significant.

What is an absence of particles called? A vacuum! No particles = no pressure Atmospheric pressure is the amount of pressure from the particles in the atmosphere colliding with objects.

Barometers A barometer measures atmospheric pressure. The first barometers were made by inverting a tube full of mercury into a dish of mercury below. The atmospheric pressure pushes the mercury in the dish, allowing the mercury in the column to stay.

Kinetic energy and temperature When a substance is heated, a small amount of energy is stored (potential energy), but most energy absorbed speeds up particles, causing faster movement and more collisions. This is a rise in temperature.

A Kinetic Voyage from Ice to Steam Which phase of matter do you think has the most kinetic energy? The least?

Solids (least KE) The particles in the solid move, but don’t move around. They vibrate around a fixed point. Most solids are crystalline—they have definite repeating structure. Substances that have more than one crystalline structure are called allotropes.

Amorphous Solids Some solids (like glass) don’t have a definite structure—they are called amorphous.

The temperature at which a solid becomes a liquid is the melting point. As kinetic energy is added to a solid, eventually the particles have so much energy that they overcome the interaction between particles and vibrate and spin themselves right out of their structure. Melting Point

Liquids In a liquid, particles vibrate and spin as they move from place to place and slide past one another. There are still intermolecular forces holding them together.

Liquids (cont.) Both liquids and gases can flow, but liquids have viscosity. Viscosity—a liquid’s resistance to flow.

Going from Liquid to Gas There are two ways in which a liquid becomes a gas. 1)Evaporation—the particles with the highest amount of kinetic energy go from liquid to gas. This is a cooling process, because it lowers the overall KE of the liquid.

Going from Liquid to Gas 2)Boiling—the boiling point is the point at which the internal vapor pressure of a liquid is equal to the external pressure. (It is also a cooling process). The boiling point is a function of BOTH temperature AND pressure.

Gases (most KE) In a gas particles move independently of each other.

Phase Diagrams Sublimation—going directly from solid to gas Triple point—the one set of conditions where a substance can exist as a solid, liquid and gas simultaneously. Phase diagram for H 2 O

Phase Diagrams, cont’d. Critical temperature—the temperature at which no matter what the pressure, it will not be a liquid (it will be gaseous) Other books define it as the point at which a liquid and gas are indistinguishable.

In Review… What is the kinetic theory? What do we assume about collisions in gases? What is gas pressure? What is the phase with the most KE? What are most solids? What is the boiling point dependent on? What is the triple point? What is sublimation?