Chapter 16

Solids, Liquids, and Gasses

Kinetic theory• Three assumptions of the Kinetic Theory

1) All matter is composed of small particles. (atoms, molecules, and ions)

2) These particles are in constant, random motion.

3) These particles are colliding with each other and the walls of their container.

Thermal Energy• You have a bowl of HOT soup. To cool it off

you might drop a cube of ice in the soup.

• Does the ice cube appear to move?

• The molecules in the ice cube are in constant motion.

• The more thermal energy… the more motion.

• All matter is in motion at a molecular level.

Average Kinetic Energy• Temperature is the term used to explain how

hot or cold an object is.

• Temperature is a measure of the average kinetic energy of a substance.

• Molecules of water will move slower at 0* C than at 100* C.

• The faster molecules are moving the warmer the substance will be.

• At -273.15 * C (0 kelvin) no more kinectic energy can be removed from a substance (absolute zero)

Solid State• An ice cube is an example of a solid.

• Solids have a definite shape and volume.

• The particles of a solid are packed closely together.

• Most solid materials have a specific geometric arrangement in which their molecules or atoms form when they are cooled from a liquid.

• Physical and chemical properties can often be attributed to this geometric arrangement.

Liquid State• What happens to a solid when thermal energy

(heat) is added to it?

• The particles of the solid start to move faster.

• The faster the particles move the farther apart they become.

• Soon the particles have enough energy to overcome the attractive forces that keep them close together and they move away from each other.

• Now the solid melts into a liquid.

• Melting Point- the temp at which a solid begins to melt or liquify.

• Heat of Fusion- the amount of energy needed to change an substance from the solid phase to the liquid phase at its melting point.

• Liquids have no definite shape but have a definite volume.

• The particles in a liquid are further apart and move faster than in solids of the same substances.

Gas State• Gasses do not have a fixed volume or shape.

• They can be compressed into whatever shape or volume the container they are in assumes.

• How does a liquid become a gas?

• Vaporization

• Vaporization can occur in two ways: evaporation and boiling.

• Evaporation occurs at the liquid’s surface and can happen below the liquids boiling point.

Boiling point• The second way a liquid can vaporize is by

boiling.

• Unlike evaporation, boiling takes place throughout the liquid.

• Boiling point- the temp at which the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of the liquid.

• Heat of vaporization is the amount of energy required for the liquid at its boiling point to become a gas.

• Diffusion- is the spreading of particles throughout a given volume until they are uniformly distributed.

• Diffusion occurs in solids and liquids but occurs most rapidly in gasses.

• If someone sprays perfume in the classroom, very soon most of the class can smell it no matter where they are.

• Why?

• Because the average oxygen molecule is traveling at 1053 mph

• This is why diffusion is fastest in gasses.

• Gasses will distribute themselves evenly in any container no matter how large or small.

• Plasma is the most common state of matter in the universe.

Thermal Expansion• The kinetic theory is used to explain the

behavior of particles in different states of matter.

• But it can also explain other characteristics of matter.

• Have you noticed the gaps in a side walk or bridge?

• These are called expansion gaps or joints.

• When concrete absorbes heat, it expands.

• This is because the molecules are moving faster and get farther apart.

• Thermal Expansion- an increase in the size of a substance when the temperature is increased.

• Expansion in liquids

• Thermal expansion takes place inside a thermometer.

• Expansion in gasses

• Hot air balloons

• Demonstration: thermal exspansion rings and bimetal strip

Behavior of Water• Water is the only exception to thermal

expansion.

• Because water is a polar compound it has a positive side and a negative side.

• This means that as water freezes the molecules line up to where there are only positives close to negatives.

• This allows spaces to reamain in the ice as it freezes.

• This is why water expands when it freezes instead of contracts like most other subsances.

Amorphous Solids• Ice melts at 0*C, gold melts at 1064*C and lead

melts at 327*C.

• But not all solids have a definite melting point.

• They just start to soften and turn into a liquid over a range of temps.

• These are called amorphous solids (without form)

• This is due to them not having a crystal structure.

• Two familiar amorphous solids: glass and plastic

Liquid Crystals• Normally the geometric arrangement of a solid

is lost when the substance goes from the solid state to a liquid state.

• Liquid crystals start to flow during the melting phase but do not lose their ordered arrangement completely.

• They retain their geometric order in specific directions.

• They are highly responsive to temp changes and electric fields.

• Liquid crystal displays (LCD) watches, calculators, and clocks.

Section 2Section 2

Properties of fluidsProperties of fluids

How do ships float?How do ships float?Aircraft carriers are huge and weigh thousands Aircraft carriers are huge and weigh thousands

of tons.of tons.So how do they float in the water?So how do they float in the water?There is a force pushing up on the ship that is There is a force pushing up on the ship that is

greater than the downward force that gravity greater than the downward force that gravity has on the ship.has on the ship.

BuoyancyBuoyancy- the ability of a fluid (liquid or gas) to - the ability of a fluid (liquid or gas) to exert an upward force on an object immersed in exert an upward force on an object immersed in it.it.

If the buoyant force is greater than or equal to If the buoyant force is greater than or equal to the weight, the object will float. If it is less than the weight, the object will float. If it is less than the objects weight, it will sink.the objects weight, it will sink.

Archimedes’ PrincipleArchimedes’ PrincipleArchimedes’ PrincipleArchimedes’ Principle- the buoyant force on an - the buoyant force on an

object is equal to the weight of the fluid object is equal to the weight of the fluid displaced by the object.displaced by the object.

If you place a block of wood in a bowl of water If you place a block of wood in a bowl of water it will push water out of the way as it sinks. But it will push water out of the way as it sinks. But only until the weight of the water displaced only until the weight of the water displaced equals the weight of the block of wood.equals the weight of the block of wood.

If the weight of the water displaced is less than If the weight of the water displaced is less than the weight of the object placed in it, the object the weight of the object placed in it, the object will sink.will sink.

DensityDensityWould a steel block the same size aws a Would a steel block the same size aws a

wood block float in water?wood block float in water?They both displace the same amount of water.They both displace the same amount of water.But the steel bar sinks while the wood floats.But the steel bar sinks while the wood floats.DensityDensity- mass per unit of volume.- mass per unit of volume.The more dense an object, the less likely it will The more dense an object, the less likely it will

be to float.be to float.But what about steel ships?But what about steel ships?The shape of the object plays an important rollThe shape of the object plays an important rollThe more area an object takes up the less The more area an object takes up the less

dense it becomes.dense it becomes.

Pascal’s PrinciplePascal’s Principle If you are under water, you can feel the If you are under water, you can feel the

pressure of the water all around you.pressure of the water all around you.PressurePressure- force exerted per unit area.- force exerted per unit area.Pascal’s PrinciplePascal’s Principle- pressure applied to a fluid is - pressure applied to a fluid is

transmitted throughout the fluid.transmitted throughout the fluid.When you squeeze the end of a balloon the When you squeeze the end of a balloon the

other end of the balloon expands.other end of the balloon expands.When you squeeze the end of the toothpaste When you squeeze the end of the toothpaste

tube, the toothpaste comes out the other end.tube, the toothpaste comes out the other end.

Bernoulli’s PrincipleBernoulli’s Principle It took humans thousands of years to learn to It took humans thousands of years to learn to

do what birds do instinctively… fly.do what birds do instinctively… fly.This ability is a property of fluids stated in This ability is a property of fluids stated in

Bernoulli’s principle.Bernoulli’s principle.Bernoulli’s PrincipleBernoulli’s Principle- as the velocity of a fluid - as the velocity of a fluid

increases, the pressure exerted by that fluid increases, the pressure exerted by that fluid decreases.decreases.

You can see bernoulli’s principle in action if you You can see bernoulli’s principle in action if you blow across the top of a sheet of paper.blow across the top of a sheet of paper.

The faster you blow the more the sheet wants The faster you blow the more the sheet wants to rise because the moving air above the sheet to rise because the moving air above the sheet exerts less pressure than the calm air below.exerts less pressure than the calm air below.

Now look at the shape of an airplane wing.Now look at the shape of an airplane wing.They are designed to create an area of low They are designed to create an area of low

pressure above the wing and high pressure pressure above the wing and high pressure below the wing.below the wing.

Now the faster the wing travels through the air, Now the faster the wing travels through the air, the more lift it will have.the more lift it will have.

Fluid FlowFluid FlowAnother property exhibited by fluids is their Another property exhibited by fluids is their

tendency to flow.tendency to flow.ViscosityViscosity- a fluid’s resistance to flow.- a fluid’s resistance to flow.The lower a fluid’s viscosity, the easier it flows.The lower a fluid’s viscosity, the easier it flows.The higher the viscosity, the slower it flows.The higher the viscosity, the slower it flows.Fluids vary in their tendency to flow because Fluids vary in their tendency to flow because

their structures differ.their structures differ.When a container is tilted to allow flow to begin When a container is tilted to allow flow to begin

the flowing particles will transfer energy to the the flowing particles will transfer energy to the particles that aren’t moving.particles that aren’t moving.

They are pulling each other, causing them to They are pulling each other, causing them to flow.flow.

If the flowing particles do not effectively pull the If the flowing particles do not effectively pull the other particles into motion, the fluid has a high other particles into motion, the fluid has a high viscosity. (high resistance to flow)viscosity. (high resistance to flow)

Basically, the higher the viscosity, the thicker Basically, the higher the viscosity, the thicker the fluid is.the fluid is.

temperature plays a roll in viscosity.temperature plays a roll in viscosity.The higher the temperature a fluid has, the The higher the temperature a fluid has, the

lower resistance to flow it will have (low lower resistance to flow it will have (low viscosity)viscosity)

The lower the temp, the higher the viscosity.The lower the temp, the higher the viscosity.

Section 2 QuizSection 2 Quiz1)1) the ability of a fluid (liquid or gas) to exert an the ability of a fluid (liquid or gas) to exert an

upward force on an object immersed in it is upward force on an object immersed in it is called ___________called ___________

2)2) the buoyant force on an object is equal to the the buoyant force on an object is equal to the weight of the fluid displaced by the object is weight of the fluid displaced by the object is called ___________ Principlecalled ___________ Principle

3)3) mass per unit of volume is _________mass per unit of volume is _________4)4) pressure applied to a fluid is transmitted pressure applied to a fluid is transmitted

throughout the fluid is _________ principlethroughout the fluid is _________ principle5)5) as the velocity of a fluid increases, the as the velocity of a fluid increases, the

pressure exerted by that fluid decreases is pressure exerted by that fluid decreases is ________ principle.________ principle.

1)1) BuoyancyBuoyancy

2)2) Archimedes’Archimedes’

3)3) DensityDensity

4)4) Pascal’sPascal’s

5)5) Bernoulli’sBernoulli’s

Section 3

• Behavior of gasses

Pressure = particle collisions• You learned from the kinetic theory that gas

particles are constantly moving and colliding with anything in their path.

• The collisions of air particles result in atmospheric pressure.

• Pressure- the amount of force per unit of area or P = F/A

• The SI unit of pressure is called the pascal (Pa)

• One pascal = one newton per square meter 1 N/m^2

• A pascal is a very small unit so we usually give most pressures in kilopascals (kPa). Or 1000 pascals.

• At sea level, atmospheric pressure is 101.3 kPa• The means 101,300 N on every square meter

(about the weight of a large truck)• When we contain a gas in a container like a tire

or balloon, they expand because of all the collisions of the air particles with the walls of the container.

• If you pump more air into the balloon there are more collisions pushing on the walls of the balloon and that makes it expand.

• If you pump more air into something that cannot expand, like an air tank, the increased air particles still slam into the walls but now instead of expanding the container, you increase the pressure inside the container.

Boyle’s Law• What happens if the amount of gas stays the

same but you decrease the size of the container?

• You know that the pressure of a gas depends on how often the particles strike the walls of their container.

• If you squeeze the gas into a smaller container the particles will strike the walls more often.

• This means the pressure will be increased.

Boyle’s Law• Boyle’s Law- if you decrease the size of the

container while the temp remains constant, the pressure will increase.

• So an increase in the size of the container while temp is constant will do what to the pressure?

• Decrease.

• Weather balloons are a perfect example.• P1V1 = constant = P2V2

Pressure-Temperature Law• You’ve seen the label keep away from heat on

spray cans.

• What happens if you heat an closed container?

• Because the can can’t expand, the pressure increases.

• If the pressure increases to a point where the can can’t contain the pressure it will explode.

Charles’s Law• If you’ve watched hot-air balloons being inflated

you know that gasses expand when they’re heated.

• Because particles in the hot air are farther apart than the particles in the cool air.

• Charles’s Law- as the temp of a gas increases the volume increases if the pressure remains constant.

• if the temp increases but the volume remains constant what will happen?

• The pressure will increase.

Quiz1) The collisions of air particles result in

________ __________

2) One pascal = one _______ per square meter

3) we usually give most pressures in ________

4) if you decrease the size of the container while the temp remains constant, the pressure will increase. This is called _________ Law

5) as the temp of a gas increases the volume increases if the pressure remains constant this is called _________ Law

1) Atmospheric pressure

2) Newton

3) Kilopascals

4) Boyles

5) Charles’s