C5.1 States of Matter: Liquids and Gases

G8 Physical Science

C5.1 Liquids and Gases

• Supplies: pencil and science notebook• Standards:

– 3d Students know the states of matter (solid, liquid, and gas, depend on molecular motion

– 3e Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.

– 5d Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.

C5.1 Liquids and Gases

• You will be taking notes using the Cornell Notes format or the Charting Notes format.

C5.1 Liquids and Gases

• Definitions• Fluid: a form of matter that flows when any

force is applied, no matter how small. Liquids and gases are fluids.

• Liquid: phase of matter that can flow and change shape but has constant volume

• Gas: phase of matter with high energy molecules that can expand to fill a container.

C5.1 Liquids and Gases

• More Definitions• Pressure: a distributed force per unit area that

acts within a fluid• Intermolecular Forces: forces between separate

atoms and molecules that are attractive at a distance but repulsive at close range.

• Melting Point: the temperature at which a substance changes from a solit to a liquid.

C5.1 Liquids and Gases

• Even More Definitions• Boiling Point: the temperature at which a

substance changes from a liquid to a gas.• Evaporation: change from liquid to gas at a

temperature below the boiling point.• Condensation: change from gas to a liquid at a

temperature below the boiling point.• Convection: the transfer of heat through the

motion of fluids such as air and water.

Liquids and Gases

• Atoms and molecules in liquids and gases

• Definition: a fluid is any matter that flows when any force is applied, no matter how small

Your Turn

• Write down the names of three liquids and three gases.

• You will use this later.

Pressure• When you apply force

to a fluid the force is distributed all over the fluid (pressure). This is what keeps ball round and allows air filled tires to support your bike.

• Pressure is caused by the collision of atoms

Your Turn

• When you apply force to one of your liquids, what happens?

• When you apply force to one of your gases, what happens?

• Do they react differently? Why or why not?

Intermolecular Force• Force 1: Holds the molecule

together• Force 2: Intermolecular

force exists between molecules.

• It is why water stays together when you spill it on the floor

• Thermal energy pushes things apart (movement) and intermolecular forces pull them together.

• In gases -- thermal energy wins

• In solids -- intermolecular forces win

Rethink

• Now that you know about intermolecular forces and heat energy. Write a better answer to the previous questions about how gases and liquids react to forces.

Melting and Boiling• Melting point is the

temperature at which a substance changes from solid to liquid.

• What substance?• Boiling point is the

temperature at which a substance changes from liquid to gas

• It takes energy to change from a solid to a liquid, or from a liquid to a gas. [cold and hot labs]

Your Turn

• Write labels on this diagram about what state the matter is in at each part of the graph.

Still Your Turn

• What is the difference between temperature and heat energy?

• Write it down.• Tell your neighbor.• Tell the class.

Melting and Boiling Points

• Water as an exception -- solid less dense than liquid

• All elements have their own freezing and boiling points

Evaporation and Condensation

• Evaporation happens when molecules go from liquid to gas at temperature below the boiling point.

• Water evaporates …• Evaporation takes

energy away from the liquid. Your skin cools when sweat evaporates.

• Condensation occurs when molecules go from gas to liquid at temperature below boiling point.

• Water condenses…• Condensation raises the

temperature because it adds energy.

• Air is saturated when evaporation and condensation happen at the same rate.

Your Turn

• Fill in the chart with where condensation and evaporation happen. Also include freezing and melting.

Convection• Convection is the transfer of

heat through the motion of fluids (which are…)

• You can see this in boiling water -- hot water rises, cool water flows down

• Forced convection is used to heat houses.

Looking Back

• Think back to 6th grade science, where have you heard about convection before?

Atmosphere

• Convection currents provide weather

• Air is nitrogen + oxygen (97%) + other stuff (but mostly nitrogen – an inert gas)

• Air pressure is due to all that air above you.

• 14.7 lbs per square inch at sea level.

Your Turn

• Have you ever driven to Tahoe with a sealed bag of potato chips in the car? What happened?

• What other effects to lower air pressure have?

Your Turn

• Draw a pressure vs. altitude graph with pressure on the x-axis and altitude on the y-axis. Use Redwood City (30.03 in Hg, 20 feet) and Tahoe City (28.17 in Hg, 6400 feet) as your two points.