1. 7.2 Temperature and the Phases of Matter
Vocabulary
Fahrenheit scale
Celsius scale
thermometer
solid
liquid
gas
Intermolecular forces
evaporation
absolute zero
Kelvin
plasma

2. Objectives Convert between temperature scales.
Explain the relationship between temperature and the movement of particles in a system.
Describe the relationship between temperature and states of matter.

3. Measuring Temperature
Fahrenheit
freezes at 32 degrees
boils at 212 degrees
Celsius
freezes at 0°C
boils at 100°C.

4. Comparison of Fahrenheit and Celsius

5. Converting Between the Scales

6. Thermometer an instrument that measures temperature

7. Temperature and Energy
Temperature is a measure of the kinetic energy.
Atoms in a solid material act like they are connected by springs

8. Average Motion
Is the motion of the whole collection or all the atoms together.
The kinetic energy that comes from the average motion of all the atoms together is not what temperature measures.

9. Random Motion
Each atom in an object jiggles back and forth independently of the other atoms.

10. Temperature and Random Motion
Temperature measures the kinetic energy in just the random motion.
Temperature is not affected by any kinetic energy associated with average motion.

11. Melting and Boiling
Even rocks can melt and boil if they have enough heat applied to them.
The higher the temperature, the higher the random kinetic energy of each atom.

12. The Phases of Matter Solid holds its shape. Liquid
holds its volume, — it flows.
Gas
flows like a liquid, but can also expand or contract to
fill a container
gas does not hold its volume

13. Plasma: A Fourth State of Matter
Temperatures greater than 10,000 °C the atoms in a gas start to break apart.
In the plasma state, matter becomes ionized.
Plasma can conduct electricity.
Ex: Lightning,
the sun, nebulas

14. Intermolecular Forces
The force that attracts molecules together when they are close.
Different strength
Their strength determine if matter exist as solid, liquid or gas.

15. Temperature vs. Intermolecular Forces
Kinetic energy from temperature tends to push molecules apart.
If temperature wins you have gas.
Intermolecular forces tend to bring molecules together.
If intermolecular forces win you have a solid.

16. Strength of Intermolecular Forces
Iron is a solid at room temperature and water is a liquid at room temperature. Which has a stronger intermolecular force? Why?

17. Changing Phase
The melting point is the temperature at which a substance changes from a solid to a liquid.
Different substances have different melting points.
Different particles have different intermolecular strength.

18. Changing Phase
Boiling takes place within the liquid as bubbles of gas particles form and rise to the surface.
Intermolecular forces are completely pulled apart.

19. Changes in State Require Energy
It takes energy to break the bonds created by intermolecular forces.

20. Absolute Zero Molecules have the lowest energy they can have.
Absolute zero occurs at minus 273°C (-459°F)
You cannot have a temperature lower than absolute zero.

21. The Kelvin Scale Useful for many scientific calculations.
Starts at absolute zero.
Measures the actual energy of atoms.

22. Converting to Kelvin Example:
Kelvin (K) unit of temperature is the same size as the Celsius unit
Add 273 to the temperature in Celsius to get the temperature in Kelvins.
Example:
21°C is equal to 294 K ( ).

23. 7.2 Section Review Page 175
A comfortable room temperature is 20ºC. What is this temperature in degrees Fahrenheit?
In which system are the molecules moving faster, a cold glass of tea or a hot cup of tea?
Describe what happens at the atomic level during melting.
Explain why particles in a gas are free to move far away from each other.