“states of matter” adapted from stephen l. cotton

““States of Matter”States of Matter”

adapted fromadapted fromStephen L. CottonStephen L. Cotton

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.

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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


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

Measuring PressureMeasuring Pressure

The first device for measuring atmosphericpressure was developed by Evangelista Torricelli during the 17th century.

The device was called a “barometer”

Baro = weight Meter = measure Torricelli

An Early An Early BarometerBarometer

760 mm Hg = 101.3 kPa = 1 atmosphere


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


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 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


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

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


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 Temp vapor pressure Temp vapor pressure


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

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Not Boiling Normal Boiling Point @ 101.3 kPa = 100 oC

Boiling, but @ 34 kPa = 70 oC

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Questions:

a. 60 oC b. about 20 kPa c. about 30 kPa

“states of matter” adapted from stephen l. cotton

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