The Nature of Gases Kinetic refers to motion Kinetic refers to motion The energy an object has because of it’s motion is called kinetic energy The energy an object has because of it’s motion is called kinetic energy The kinetic theory states that the tiny particles in all forms of matter are in constant motion! The kinetic theory states that the tiny particles in all forms of matter are in constant motion!

KMT – Kinetic Molecular Theory 1. All matter is composed of very tiny particles 1. All matter is composed of very tiny particles 2. Particles of matter are continually moving 2. Particles of matter are continually moving 3. The collisions of these particles are “elastic” (no loss of energy) 3. The collisions of these particles are “elastic” (no loss of energy)

The Nature of Gases Three basic assumptions of the kinetic theory as it applies to gases: Three basic assumptions of the kinetic theory as it applies to gases: #1. The particles in a gas are considered to be small, hard spheres with insignificant volume #1. The particles in a gas are considered to be small, hard spheres with insignificant volume #2. The motion of the particles in a gas are rapid, constant and random #3. All collisions between particles in a gas are perfectly elastic.

The Nature of Gases (no volume or shape) Gas Pressure –the force exerted by a gas per unit surface area of an object Gas Pressure –the force exerted by a gas per unit surface area of an object The result of simultaneous collisions of billions of rapidly moving particles. The result of simultaneous collisions of billions of rapidly moving particles. No particles present? Then there cannot be any collisions, and thus no pressure – called a vacuum No particles present? Then there cannot be any collisions, and thus no pressure – called a vacuum

The Nature of Gases Atmospheric pressure results from the collisions of air molecules with objects Atmospheric pressure results from the collisions of air molecules with objects Air exerts pressure on earth because gravity holds the particles in the air from Earth’s atmosphere. Air exerts pressure on earth because gravity holds the particles in the air from Earth’s atmosphere. Barometer is the measuring device for atmospheric pressure, which is dependent upon weather & altitude Barometer is the measuring device for atmospheric pressure, which is dependent upon weather & altitude

An Early Barometer 760 mm Hg = kPa = 1 atmosphere

The Nature of Gases For gases, it is important to relate measured values to standards For gases, it is important to relate measured values to standards Standard values are defined as a temperature of 0 o C and a pressure of kPa, or 1 atm Standard values are defined as a temperature of 0 o C and a pressure of kPa, or 1 atm This is called Standard Temperature and Pressure, or STP This is called Standard Temperature and Pressure, or STP

The Nature of Gases Absolute zero (0 K, or –273 o C) is the temperature at which the motion of particles theoretically ceases Absolute zero (0 K, or –273 o C) is the temperature at which the motion of particles theoretically ceases Kelvin = °C Kelvin = °C °C = Kelvin – 273 °C = Kelvin – 273 °C = (°F – 32) x.555 °C = (°F – 32) x.555

The Nature of Gases The Kelvin temperature scale reflects a direct relationship between temperature and average kinetic energy The Kelvin temperature scale reflects a direct relationship between temperature and average kinetic energy Particles of He gas at 200 K have twice the average kinetic energy as particles of He gas at 100 K Particles of He gas at 200 K have twice the average kinetic energy as particles of He gas at 100 K

The Nature of Liquids Liquid particles are also in motion. Liquid particles are also in motion. a phase of a substance that has a definite volume but no definite shape a phase of a substance that has a definite volume but no definite shape

The Nature of Liquids vaporization vaporization – conversion of a liquid to a gas by adding heat evaporation evaporation – conversion of a liquid to a gas at room temperature

The Nature of Liquids Evaporation of a liquid in a closed container is somewhat different Evaporation of a liquid in a closed container is somewhat different vapor pressurea measure of the force exerted by a gas above a liquid vapor pressure – a measure of the force exerted by a gas above a liquid An increase in the temperature of a liquid increases the vapor pressure. A decrease in the temperature decreases the vapor pressure.

The Nature of Liquids The boiling point (bp) the temperature at which the vapor pressure of a liquid is just equal to the external pressure. The boiling point (bp) the temperature at which the vapor pressure of a liquid is just equal to the external pressure.

Section 13.2 The Nature of Liquids Normal bp of water = 100 o C Normal bp of water = 100 o C However, in Denver = 95 o C, since Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa (Recipe adjustments?) However, in Denver = 95 o C, since Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa (Recipe adjustments?) In pressure cookers, which reduce cooking time, water boils above 100 o C due to the increased pressure In pressure cookers, which reduce cooking time, water boils above 100 o C due to the increased pressure

- Page 394 Not Boiling Normal Boiling kPa = 100 o C Boiling, 34 kPa = 70 o C

The Nature of Solids SOLID – a substance that has definite shape and volume SOLID – a substance that has definite shape and volume

The Nature of Solids Allotropes are two or more different molecular forms of the same element in the same physical state Allotropes are two or more different molecular forms of the same element in the same physical state ex. Carbon – graphite, diamond, Fullerene ex. Carbon – graphite, diamond, Fullerene Not all solids are crystalline, but instead are amorphous Not all solids are crystalline, but instead are amorphous

The Nature of Solids Crystalline Solid: Crystalline Solid: solids arranged in an orderly repeating 3-d pattern (ex. Diamonds, salt crystals, sugar crystals)

The Nature of Solids Amorphous Solids: a solid that lacks an ordered internal structure (ex. Rubber, plastic, silly putty)

Heating Curve

The Nature of Solids At the melting point, the disruptive vibrations are strong enough to overcome the interactions holding them in a fixed position At the melting point, the disruptive vibrations are strong enough to overcome the interactions holding them in a fixed position Melting point can be reversed by cooling the liquid so it freezes Melting point can be reversed by cooling the liquid so it freezes Solid liquid Solid liquid