The Kinetic Molecular Theory Review Notes Tuesday, April 3rd, 2018

Review Matter can exist in several states: Solids have a definite shape and volume, and are not compressible. Liquids have a definite volume but not a definite shape. They are not compressible. Gases do not have a definite shape or volume. Gases are compressible.

Particles in Solids, Liquids, and Gases The motion of gas molecules is rapid, constant, and random.

Chemical identity Temperature Pressure States of Matter The state (solid, liquid, or gas) of a substance depends on three things: Chemical identity Temperature Pressure

States of Matter In solids, attractive forces outweigh kinetic energy of particles. Particles stick together in rigid position. In liquids, attractive forces are balanced by kinetic energy. Particles stick together but can move past each other. In gases, kinetic energy outweighs attractive forces. Particles fly rapidly past each other as if there are no attractive forces between them.

The Kinetic Molecular Theory Kinetic molecular theory (KMT): Explains the observed properties of matter in its different states. Particles are in constant, rapid, random motion. The speed of this motion depends on temperature. Collisions between particles are elastic. (No kinetic energy lost).

The Kinetic Molecular Theory In a perfectly elastic collision, the kinetic energy of each molecule might change, but the total kinetic energy stays the same. Collisions between particles are elastic.

Pressure Pressure = force / area

Pressure One gas molecule exerts a tiny force against the side of a balloon.

Pressure When you have a huge number of gas molecules colliding against the sides of a balloon, the force adds up. Force spread out over the inner surface of the balloon is pressure.

Standard Pressure Standard Pressure = 1 atm Standard pressure is the normal air pressure at sea level.

Pressure Conversion Factors 1 atm = 760 mmHg 1 atm = 101.3 kPa 1 atm = 14.7 psi 1 atm = 760 torr

Atmospheric Pressure As you move upward through the atmosphere, the density decreases. This is because most air molecules are held close to Earth’s surface by gravity. As the density decreases, there are fewer molecules colliding with surfaces; hence, less pressure.

Temperature Temperature – measure of the average kinetic energy of a substance’s molecules. The molecules in a hot object are moving faster than the molecules in a cold object on average!

Temperature Absolute temp. is measured in Kelvins (K) To convert: No degree symbol! To convert: from °C to K. K = °C + 273 from °C to °F °F = 9/5 (°C) + 32 from °F to °C °C = 5/9 (°F – 32) EXAMPLE: Water boils at 100°C, or 373 K. Water freezes at 0°C, or 32°F. Avg. human body temp. is 97.8°F, or 36.5°C.

Standard Temperature Standard Temperature = 0°C. Also, 273 K. Absolute Zero = -273°C = 0 K. Lowest temperature. All molecular motion stops.

Kinetic Molecular Theory (KMT) explains why gases behave as they do deals w/“ideal” gas particles… 1. …are so small that they are assumed to have zero volume …are in constant, straight-line motion …experience elastic collisions in which no energy is lost …have no attractive or repulsive forces toward each other …have an average kinetic energy (KE) that is proportional to the absolute temp. of gas (i.e., Kelvin temp.) AS TEMP. , KE

Characteristics of Gases Gases expand to fill any container. random motion, no attraction Gases are fluids (like liquids). no attraction Gases have very low densities. no volume = lots of empty space Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Characteristics of Gases Gases can be compressed. no volume = lots of empty space Gases undergo diffusion & effusion. random motion Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem