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 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.