3.1 Solids, Liquids, and Gases

Kinetic energy:

Energy an object has due to its motion.

Kinetic Theory

Kinetic theory of matter:

All particles of matter are in constant motion.

3.1 Solids, Liquids, and Gases

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.

Kinetic Theory

3.1 Solids, Liquids, and 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.

Explaining the Behavior of Gases

3.1 Solids, Liquids, and Gases

Photograph taken just after cue stick struck the white ball, which began to move.

Explaining the Behavior of Gases

White ball moved in straight line until it collided with dark blue ball.

3.1 Solids, Liquids, and 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

Explaining the Behavior of Gases

3.1 Solids, Liquids, and 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.

Explaining the Behavior of Gases

3.1 Solids, Liquids, and 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.

Explaining the Behavior of Gases

3.1 Solids, Liquids, and 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

Explaining the Behavior of Gases

3.1 Solids, Liquids, and 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.

Explaining the Behavior of GasesKinetic Theory of Gases

3.1 Solids, Liquids, and Gases

•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?

Explaining the Behavior of Liquids

3.1 Solids, Liquids, and Gases

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 1/50th

speed of helium atom to have same kinetic energy.

Why Mercury a liquid instead of a gas at room temp

3.1 Solids, Liquids, and Gases

•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.

Why Mercury a liquid instead of a gas at room temp

3.1 Solids, Liquids, and Gases

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

Explaining the Behavior of Liquids

3.1 Solids, Liquids, and Gases

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

Explaining the Behavior of Liquids

3.1 Solids, Liquids, and Gases

Solids have definite volume and definite shape because particles vibrate around fixed locations.

Explaining the Behavior of Solids

3.1 Solids, Liquids, and Gases

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.

Explaining the Behavior of Solids

3.1 Solids, Liquids, and Gases

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.

Explaining the Behavior of Solids

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 Questions2. 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 in a gas are arranged in an orderly fashion.

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.