1. Ch. 13 States of Matter
Ch The Nature of Gases

2. Kinetic Theory and a Model for Gases
Kinetic energy—the energy an object has because of its motion.
Assumptions about gases:
The particles in a gas are considered to be small hard spheres with an insignificant volume.
The motion of the particles in a gas is rapid, constant, and random.

3. All collisions between particles in a gas are perfectly elastic (no energy is lost).

4. 3 states of matter: solid, liquid, gas

5. Motion in gases vs solids
gases solids

6. Gas Pressure
Gas pressure results 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.
Vacuum—an empty space with no particles and no pressure.

7. Atmospheric Pressure—results from collisions of atoms and molecules in air with objects. Decreases with increasing elevation.
Barometers measure atmospheric pressure. Normal atmospheric pressure at sea level can push mercury up a vacuum tube to a height of 760 mm.

9. Pascal (Pa)—the SI unit of pressure. Very small unit. Normal atm
Pascal (Pa)—the SI unit of pressure. Very small unit. Normal atm. pressure is about 100,000 Pa.
One standard atmosphere (1 atm) = 760 mm Hg = kPa at 25C.
Pressure units conversion problems…

10. Kinetic Energy and Temperature
Higher temperature of a substance means there is a higher average speed, or kinetic energy, of its atoms or molecules.
At any given temperature, all substances, regardless of state, have the same average kinetic energy.
Temperature is directly related to the average kinetic energy of a substances’ particles.

11. Absolute zero—no particle motion; no kinetic energy. 0 K. -273. 15C
Absolute zero—no particle motion; no kinetic energy. 0 K C. Never produced in the laboratory.
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the substance.