c5.1 states of matter: liquids and gases g8 physical science
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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.