The Nature of Gases

States of Matter Solid – matter that has a definite shape and volume. Liquid – form of matter that flows, has a fixed volume, and takes the shape of it’s container. Plasma - typically an ionized gas. “Ionized" refers to presence of one or more free electrons. The free electrons make the plasma respond strongly to electromagnetic fields. GAS – form of matter that has no definite shape or volume; it adopts the shape and volume of it’s container.

Gases Kinetic Theory Gas Pressure Standard Temperature and Pressure Kinetic Energy and Kelvin Temperature

Kinetic Theory The energy an object has because of its’ motion. Tiny particles in all forms of matter are in constant motion. A gas is composed of particles, usually molecules or atoms. The particles in a gas move rapidly in constant random motion. These particles change direction only when they rebound from collisions with one another or with other objects (e.g., walls of a container). All collisions are elastic.

Gas Pressure Defined as the force exerted by a gas per unit surface area of an object. Atmospheric pressure results from collisions of air molecules with objects. (What holds these molecules in place?) Barometers are devices commonly used to measure atmospheric pressure. (DEMOS!) SI unit is the pascal (Pa), at sea level (one standard atmosphere) the pressure (STP) is 101.3 kPa = 760mm Hg = 14.7 psi = 1 atm at 25 oC.

Kinetic Energy and Kelvin Temperature When a substance is heated, the particles absorb energy, some of which is stored in the particles. Stored energy does not cause temp to increase (potential energy). Remaining energy speeds up the particles (kinetic energy) This increase in the Average Kinetic Energy causes the temperature of the substance to rise.

Sample Problem 10.1 S A M P L E R O B

Sample Problem 10.1 S A M P L E

Sample Problem 10.1 S A M P L E

Sample Problem 10.1 Convert to psi using the conversion that one atmosphere = 14.7 psi.

Discussion What else, besides a temperature change, will cause gas pressure to increase?

Discussion Points One Step Further Will the temperature of the substance always increase as energy is added to the substance? What are some practical examples of this phenomena? What happens to boiling points as the pressure is decreased? (e.g., Water)