States of Matter: Liquids and Gases

1. States of Matter: Liquids and Gases Physical Science Chapter 5.1

2. 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

3. Your Turn • Write down the names of three liquids and three gases. • You will use this later.

4. Forces in Fluids • Definition: pressure is a distribute force per unit area that acts within a fluid • 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

5. 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?

6. 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

7. 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.

8. 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]

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

10. Still Your Turn • What is the difference between temperature and heat energy? • Write it down. • Tell your neighbor. • Tell the class.

11. Melting and Boiling Points • Water as an exception -- solid less dense than liquid • All elements have their own freezing and boiling points

12. 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.

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

14. 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.

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

16. 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.

17. 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?

18. 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.