3.1 Solids, Liquids, and Gases Kinetic Theory Kinetic energy: Energy an object has due to its motion.

Kinetic theory of matter: All particles of matter are in constant motion.

3.1 Solids, Liquids, and Gases Kinetic Theory

A ball thrown at 137 kilometers per hour has more kinetic energy than a ball thrown at 100 kilometers per hour. The kinetic theory was developed to explain the behavior of gases. It can also help to explain the behavior of liquids and solids.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases

Motion of billiard balls can be compared to motion of particles in a gas.

• Cue stick strikes a ball  Ball moves in straight line until it strikes something (side of table or another ball) • When moving ball strikes a ball at rest  First ball slows down; second ball begins to move.

Kinetic energy is transferred during collisions.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases

Photograph taken just after cue stick struck the white ball, which began to move. White ball moved in straight line until it collided with dark blue ball.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases Motion in Gases

Unlike billiard balls ,

particles in a gas are never at rest

. • Avg speed of gas particles at room temp = ~1,600 km/hr (1,600 km/hr = ~1,000 mph) • (Speed of sound is ~1,250 km/hr = ~770 mph) • Not all particles are moving at same speed.

Particles are constantly changing speed and direction through collisions

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases

Illustration shows paths of two atoms in a container of gas.

•

Atoms move in straight lines until colliding

(with each other or container) • If one atom loses kinetic energy, other atom gains kinetic energy  • no net change no overall energy.

Total kinetic energy of the atoms remains the same

.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases There are forces of attraction among the particles in all matter.

• Between collisions, why doesn’t one particle in a gas attract the other particles in the gas?

Gas particles far apart and moving fast



attractions are too weak to have an effect

. – Under ordinary conditions, scientists ignore the forces of attraction in a gas.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases Motion in Gases – Summary 1) Particles in a gas are never at rest

.

2) Atoms move in straight lines until colliding.

3) Total kinetic energy of atoms remains same

.

4) Gas particles far apart and moving fast



attractions are too weak to have an effect

.

• http://en.wikipedia.org/wiki/Image:Translational_motion.gif

3.1 Solids, Liquids, and Gases Explaining the Behavior of Gases Kinetic Theory of Gases

Kinetic theory explains general properties of gas: –

Constant motion of particles +

–

Minimal attraction between particles

 –

Gas fills a container of any shape or size.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Liquids

•

Particles in liquids have kinetic energy, too

•

All materials at a given temperature have the same average kinetic energy.

So, at room temp, why is mercury a liquid & helium a gas?

3.1 Solids, Liquids, and Gases Why Mercury a liquid instead of a gas at room temp

At room temp, why is mercury a liquid & helium a gas?

– Reminder: liquids have definite volume and gasses expand to fill the container •Mercury atoms much heavier than helium atoms • He atomic weight ~4 atomic units • Hg atomic weight ~200 atomic units (50X heavier)

To have same kinetic energy, mercury must move much slower than helium.

• Think of impact from bowling balls vs tennis balls • To have same impact, bowling balls move much slower • Average speed of mercury atom can only be 1/50 th speed of helium atom to have same kinetic energy.

3.1 Solids, Liquids, and Gases Why Mercury a liquid instead of a gas at room temp

•

To have same kinetic energy, mercury atoms must move much slower than helium atoms.

• Particles in liquid move slower than particles in gas.

• Particles in liquid are much closer than particles in gas.

•Unlike gasses,

attractions between particles in a liquid DO affect movement of the particles.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Liquids

• •

VARIABLE SHAPE

(not definite) because

particles Can flow to new locations.

Move in straight lines until they collide

(with walls or each other) - just like gasses •

FIXED VOLUME

because

Forces of attraction keep particles close together

unlike gasses

3.1 Solids, Liquids, and Gases Explaining the Behavior of Liquids

Kinetic theory explains general properties of liquids: –

Constant motion of particles

–

+ Forces of attraction limiting motion of particles

 –

Liquids:

• •

Conform to container’s shape Can’t expand volume to completely fill large container

3.1 Solids, Liquids, and Gases Explaining the Behavior of Solids Solids have definite volume and definite shape because particles vibrate around fixed locations.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Solids Vibration is a repetitive back-and-forth motion

. • Strong attractions restrict atoms’ motion •

Each atom stays in a fixed location relative to its neighbors

. • Each atom vibrates around its location, but it does not exchange places with a neighboring atom.

3.1 Solids, Liquids, and Gases Explaining the Behavior of Solids

During a movie people move around in their seats, but each person remains in essentially the same location.

“Particles” have “fixed” locations - total volume doesn’t change.

3.1 Solids, Liquids, and Gases Exit Slip Questions WRITE OUT QUESTIONS AND ANSWERS 1. Materials are classified as solids, liquids, or gases based on their: a) temperature and density characteristics

.

b) chemical composition.

c) shape and volume characteristics

.

d) reactivity.

3.1 Solids, Liquids, and Gases Exit Questions 2. Describe

gasses

based on the kinetic theory

:

a) Particles

of gas are

in motion part of the time and stationary part of the time

.

b) Particles fashion.

in a gas

are arranged in an orderly

c) Gas

particles are not affected by collisions

with other gas particles.

d) Forces of attraction

between particles can be

ignored under ordinary conditions.

3.1 Solids, Liquids, and Gases Exit Questions 3. When gas particles collide with each other:

a) Particles

change their paths

.

b) One

of the particles

stops moving

.

c) Net kinetic energy is changed

.

d) All of the above

.

3.1 Solids, Liquids, and Gases Exit Questions 4. Particles in a liquid: a) All

have exactly the

same kinetic energy

.

b) Are

not very strongly attracted

to each other.

c) Move in straight lines

until they collide with walls or each other.

d) Stay in fixed locations

relative to their neighbors.

3.1 Solids, Liquids, and Gases Exit Questions 5. Particles in a solid: a) All

have exactly the

same kinetic energy

.

b) Are

not very strongly attracted

to each other.

c) Move in straight lines

until they collide with walls or each other

d) Stay in fixed locations

relative to their neighbors.