The Nature of Gases Kinetic Kinetic – means motion Kinetic Energy Kinetic Energy – the energy an...

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The Nature of The Nature of Gases Gases Kinetic Kinetic – means motion Kinetic Energy Kinetic Energy – the energy an object has because of its motion. Kinetic Theory Kinetic Theory – all matter consists of tiny particles that are in constant motion.

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1. A gas is composed of particles u molecules or atoms u Considered to be hard spheres far enough apart that we can ignore their volume. u Between the molecules is empty space. The Kinetic Theory of Gases Makes three descriptions of gas particles

Transcript of The Nature of Gases Kinetic Kinetic – means motion Kinetic Energy Kinetic Energy – the energy an...

Page 1: The Nature of Gases Kinetic Kinetic – means motion Kinetic Energy Kinetic Energy – the energy an object has because of its motion. Kinetic Theory Kinetic.

The Nature of GasesThe Nature of Gases

Kinetic Kinetic – means motion

Kinetic EnergyKinetic Energy – the energy an object has because of its motion.

Kinetic TheoryKinetic Theory – all matter consists of tiny particles that are in constant motion.

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Kinetic Theory

Kinetic theory says that molecules are in constant motion.

Perfume molecules moving across the room are evidence of this.

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1. A gas is composed of particles molecules or atoms Considered to be hard spheres far

enough apart that we can ignore their volume.

Between the molecules is empty space.

The Kinetic Theory of GasesMakes three descriptions of gas particles

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2. The particles are in constant random motion.

Move in straight lines until they bounce off each other or the walls.

3. All collisions are perfectly elastic

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The Average speed of an oxygen molecule is 1656 km/hr at 20ºC

The molecules don’t travel very far without hitting each other so they move in random directions.

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Pressure Pressure is the result of collisions of the

molecules with the sides of a container. A vacuum is completely empty space -

it has no pressure. Pressure is measured in units of

atmospheres (atm). It is measured with a device called a

barometer.

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Barometer At one atmosphere

pressure a column of mercury 760 mm high.

Dish of Mercury

Column of Mercury

1 atm Pressure

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Barometer At one atmosphere

pressure a column of mercury 760 mm high.

A second unit of pressure is mm Hg

1 atm = 760 mm Hg Third unit is the

Pascal 1 atm = 101.3 kPa

760 mm1 atm Pressure

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Pressure units kilopascals – kPa 1 atm = 760 mm Hg = 101.3 kPa

Convert 743 mm Hg to atm

895 kPa to mm Hg

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Gas PressureGas Pressure

Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.

• e.g. – a helium-filled balloon maintains its shape because of the pressure of the gas within it.

• Vacuum – an empty space with no particles and no

pressure. (no particles, no collisions)

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Atmospheric PressureAtmospheric Pressure

Atmospheric pressureAtmospheric pressure results from the collisions of atoms and molecules in air with objects. • Atmospheric pressure decreases as you climb

a mountain because the density of Earth’s atmosphere decreases as elevation increases.

• less particles, less pressure

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The Nature of LiquidsThe Nature of Liquids Particles are in motion.

• Tends to pull them apart Attractive forces between molecules

keep them close together. liquids are much more dense than

gases. These are called intermolecular

forces.• Inter = between

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Vaporization - the change from a liquid to a gas below its boiling point.

Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).

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EvaporationEvaporation Molecules at the surface break

away and become gas.

Only those with enough KE escape

It requires energy.

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Solids Intermolecular forces are strong Molecules still move Can only vibrate and revolve in place. Particles are locked in place - don’t

flow. Melting point is the temperature where

a solid turns into a liquid. The melting point is the same as the

freezing point.

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Phase Changes

Solid

Liquid

Gas

Melting Vaporization

Condensation

Freezing

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Sublimation – the change of a substance from a solid to a vapor without passing through the liquid state.

Sublimation can occur because solids, like liquids, have vapor pressure.

Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.

SublimationSublimation

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For example:

• Solid carbon dioxide (dry ice) sublimes at atmospheric pressure.

• Used as a coolant. It does not produce a liquid as ordinary ice does when it melts.

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Liquid

Sublimation

Melting Vaporization

Deposition

Condensation

Solid

Freezing

Gas

Require energy

Release energy

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End of Chapter 13End of Chapter 13