The Nature of GasesThe Nature of Gases

KineticKinetic refers to motion refers to motion The energy an object has The energy an object has

because of it’s motion is called because of it’s motion is called kinetic energykinetic energy

The The kinetic theorykinetic theory states that the states that the tiny particles in tiny particles in all forms of matterall forms of matter are in are in constant motionconstant motion!!

KMT – Kinetic Molecular KMT – Kinetic Molecular TheoryTheory

1. All matter is composed of 1. All matter is composed of very tiny particles very tiny particles

2. Particles of matter are 2. Particles of matter are continually movingcontinually moving

3. The collisions of these 3. The collisions of these particles are “elastic” (no particles are “elastic” (no loss of energy)loss of energy)

The Nature of GasesThe Nature of Gases Three basic assumptionsThree basic assumptions of the kinetic of the kinetic

theory as it applies to gases:theory as it applies to gases:

#1#1. The particles in a gas are . The particles in a gas are considered to be small, hard spheres considered to be small, hard spheres with insignificant volumewith insignificant volume#2. The motion of the particles in a gas #2. The motion of the particles in a gas are rapid, constant and randomare rapid, constant and random#3. All collisions between particles in a #3. All collisions between particles in a gas are perfectly elastic.gas are perfectly elastic.

The Nature of Gases (no The Nature of Gases (no volume or shape)volume or shape)

Gas PressureGas Pressure –the force exerted by –the force exerted by a gas per unit surface area of an a gas per unit surface area of an objectobject The result of simultaneous collisions The result of simultaneous collisions

of billions of rapidly moving particles.of billions of rapidly moving particles. No particles present? Then there No particles present? Then there

cannot be any collisions, and thus no cannot be any collisions, and thus no pressure – called a pressure – called a vacuumvacuum

The Nature of GasesThe Nature of Gases

Atmospheric pressureAtmospheric pressure results from results from the collisions of air molecules with the collisions of air molecules with objectsobjects Air exerts pressure on earth because Air exerts pressure on earth because

gravity holds the particles in the air gravity holds the particles in the air from Earth’s atmosphere.from Earth’s atmosphere.

BarometerBarometer is the measuring device is the measuring device for atmospheric pressure, which is for atmospheric pressure, which is dependent upon weather & altitudedependent upon weather & altitude

An Early An Early BarometerBarometer

760 mm Hg = 101.3 kPa = 1 atmosphere

The Nature of GasesThe Nature of Gases

For gases, it is important to relate For gases, it is important to relate measured values to standardsmeasured values to standards Standard values are defined as a Standard values are defined as a

temperature of 0temperature of 0 o oC and a pressure of C and a pressure of 101.3 kPa, or 1 atm101.3 kPa, or 1 atm

This is called This is called Standard Standard Temperature and PressureTemperature and Pressure, or , or STPSTP

The Nature of GasesThe Nature of Gases

Absolute zeroAbsolute zero (0 K, or –273 (0 K, or –273 ooC) is the C) is the temperature at which the motion of temperature at which the motion of particles particles theoretically ceasestheoretically ceases

Kelvin = °C + 273Kelvin = °C + 273 °C = Kelvin – 273 °C = Kelvin – 273 °C = (°F – 32) x .555°C = (°F – 32) x .555

The Nature of GasesThe Nature of Gases

The Kelvin temperature scale The Kelvin temperature scale reflects a reflects a direct relationshipdirect relationship between temperature and average between temperature and average kinetic energykinetic energyParticles of He gas at 200 K have Particles of He gas at 200 K have

twice the average kinetic energytwice the average kinetic energy as particles of He gas at 100 Kas particles of He gas at 100 K

The Nature of LiquidsThe Nature of Liquids

Liquid particlesLiquid particles are also in motion. are also in motion. a phase of a substance that has a phase of a substance that has

a definite volume but no definite a definite volume but no definite shapeshape

The Nature of LiquidsThe Nature of Liquids

vaporizationvaporization – conversion of a liquid to a gas by adding heat

evaporationevaporation – conversion of a liquid to a gas at room temperature

The Nature of LiquidsThe Nature of Liquids

Evaporation of a liquid in a closed Evaporation of a liquid in a closed container is somewhat differentcontainer is somewhat different vapor pressurevapor pressure – a measure of the a measure of the

force exerted by a gas above a liquid 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 LiquidsThe Nature of Liquids

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

Section 13.2Section 13.2The Nature of LiquidsThe Nature of Liquids

Normal bp of water = 100 Normal bp of water = 100 ooCC However, in Denver = 95 However, in Denver = 95 ooC, since C, since

Denver is 1600 m above sea level and Denver is 1600 m above sea level and average atmospheric pressure is about average atmospheric pressure is about 85.3 kPa (Recipe adjustments?)85.3 kPa (Recipe adjustments?)

In In pressure cookerspressure cookers, which reduce , which reduce cooking time, water boils cooking time, water boils aboveabove 100 100 ooC C due to the increased pressuredue to the increased pressure

- Page 394

Not Boiling Normal Boiling Point @ 101.3 kPa = 100 oC

Boiling, but @ 34 kPa = 70 oC

The Nature of SolidsThe Nature of Solids

SOLIDSOLID – a substance that has – a substance that has definite shape and volumedefinite shape and volume

The Nature of SolidsThe Nature of Solids

AllotropesAllotropes are two or more different are two or more different molecular forms of the same molecular forms of the same element in the same physical stateelement in the same physical state ex. Carbon – graphite, diamond, ex. Carbon – graphite, diamond,

FullereneFullerene Not all solids are crystalline, but Not all solids are crystalline, but

instead are instead are amorphousamorphous

The Nature of SolidsThe Nature of SolidsCrystalline SolidCrystalline Solid:: solids arranged

in an orderly repeating 3-d pattern (ex. Diamonds, salt crystals, sugar crystals)

The Nature of SolidsThe Nature of Solids

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

Heating CurveHeating Curve

The Nature of SolidsThe Nature of Solids

At the melting point, the disruptive At the melting point, the disruptive vibrations are strong enough to vibrations are strong enough to overcome the interactions holding overcome the interactions holding them in a fixed positionthem in a fixed position Melting point can be reversed by Melting point can be reversed by

cooling the liquid so it cooling the liquid so it freezesfreezes Solid liquidSolid liquid