Chapter 13.1 The Nature of Gases

Kinetic Theory and a Model for Gases Kinetic energy is the energy of an object because of its motion. The kinetic theory - all matter is made of tiny particles that are in constant motion. The particles in a gas are considered to be small, hard spheres with an insignificant volume. The particles are far apart in gas, compared to a liquid or solid. There is empty space between the particles and particle motion is independent of other particles.

All collisions between particles in a gas are perfectly elastic All collisions between particles in a gas are perfectly elastic. This means that kinetic energy is transferred without loss from one particle to another, so that the total kinetic energy stays constant.

Gas Pressure Gas pressure is a result from the force exerted by a gas per unit surface area of an object. Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object. A vacuum is an empty space with no particles and no pressure.

Air pressure is a type of gas pressure Air pressure is a type of gas pressure. The air is exerting force on the Earth. Atmospheric pressure is the result of the collision of molecules and atoms in the air with objects. This pressure decreases as you climb a mountain because there is less air above you the higher you go. A barometer is used to measure atmospheric pressure.

Barometer

The SI unit for pressure is pascal (Pa) The SI unit for pressure is pascal (Pa). We can also use millimeters of mercury (mm Hg) and atmospheres. One standard atmosphere (atm) is the pressure required to support 760 mm Hg in a barometer at 25 degrees Celsius. 1 atm = 760 mm Hg = 101.3 kPa Remember standard temperature and pressure (STP) is a temperature of 0 degrees Celsius and a pressure of 101.3 kPa, or 1 atm.

Kinetic Energy and Temperature Any substance that is heated - the particles absorb energy and stores some of the energy. This stored energy does not raise the temperature it just speeds the particles up. The increased kinetic energy results in an increase in temperature.

Average Kinetic Energy We use the average kinetic energy of a substance because all of the particles in the substance move at different rates. There is a relationship between the average kinetic energy and temperature. As average kinetic energy increases the substances energy increases. A decrease in average kinetic energy is a decrease in temperature.

Absolute Zero Absolute zero is the temperature at which the motion of particles theoretically stops. There is no temperature lower than absolute temperature. Absolute zero has never be achieved in a lab.

Average Kinetic Energy and Kelvin Temperature The Kelvin temperature scale shows the relationship between temperature and average kinetic energy. The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles in the substance.