Heat Unit chapters 9 and 10

1. Heat Unit chapters 9 and 10 First Chapter 9 Pages 134-150

2. Thermal Energy • What is matter? • Matter is anything that has mass. • Mass is composed of atoms. • These atoms are constantly moving. • The state of matter decides how fast these atoms move. • The movement of these atoms produces energy.

3. Thermal Energy Definition • Thermal energy in a substance is the total energy of all its atoms and molecules. • What does this really look like? • Let’s find out!

4. In Terms of Thermal Energy • Hot vapors are composed of molecules traveling very fast. • HIGH THERMAL ENERGY • Liquids are composed of molecules that travel fast. • MEDIUM THERMAL ENERGY • Solids are composed of molecules that travel slowly. • LOW THERMAL ENERGY

5. Temperature • Definition: • the degree of hotness or coldness of a body or environment (corresponding to its molecular activity) • Molecular activity can be defined as movement (expansion or contraction)

6. Temperature • A molecule is something that is composed of two or more atoms. • Temperature is related to the random motion of molecules. • Temperature is proportional to the average kinetic energy of the molecules.

7. Celsius Hundred step scale 0º C freezing point 100ºC boiling point Named after Anders Celsius (1701-1744) Used in all countries that use metric system Fahrenheit Used in the USA 32ºF freezing point 212ºF boiling point Named after Gabriel Fahrenheit (1686-1736) Temperature

8. Question • What is the difference between thermal energy and temperature?

9. Kelvin Scale • The absolute scale • Kelvin cannot be negative. • 0 K=-273ºC • Conversion: • K=C+273 • At 0 K, no molecular movement is possible • Absolute Zero

10. Kelvin • Named after British physicist, Lord Kelvin • Absolute zero is a limit. • A limit is something that cannot be reached. • Today’s technology can get close to absolute zero, but not reach it.

11. Homework (due THURSDAY!) • Complete RQ 1-7 pg 148 • If you want a head start, do them all!

12. Heat • Direction of heat flow is ALWAYS from hot to cold. • Heat is the movement of thermal energy due to a temperature difference between objects. • Rubbing hands produces heat. Does the object have heat in it? Why or why not?

13. Heat and Thermal Energy • Example: Drop a red hot piece of metal into a large bucket of warm water. • Thermal energy does not flow from the water to the metal, but from the HOT metal to the COLD water. • Heat will flow until objects reach equilibrium.

14. Cold • Cold is the absence of thermal energy like black is the absence of light. • Remember that heat travels from hot to cold. • Therefore cold does not travel at all because its not “a thing” itself.

15. Question • Suppose you apply a flame to 1 L of water and its temperature rises by 3°C. If you apply the same flame for the same length of time to 3 L of water, by how much does its temperature rise? • Why?

16. Units of Energy • Energy is measured in joules • 4.18 J of heat=1 calorie • A calorie is the energy required to change the temperature 1°C of 1 gram of water. • A Calorie is 1000 calories

17. Homework • RQ 1-12 pg 148-149

18. Rules to Energy • With everything in life, there are always rules to follow. • These rules, or laws, are called the Laws of Thermodynamics. • This is just a way to say why and how thermal energy behaves.

19. The 1st Law of Thermodynamics • Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. • What is a system? • This law really means that you are not powerful enough to create energy, you just reuse it.

20. The 2nd Law of Thermodynamics • Heat never spontaneously flows from a cold substance to a hot substance. • Two examples: • Keep the doors shut in the winter and the summer. • Listen to your parents (They know science after all!)

21. The Third Law of Thermodynamics • No system can reach absolute zero. • Why? Because it’s the lower limit of temperature. • Scientists have came close, 1 millionth of a Kelvin close.

22. Specific Heat Capacity • Different substances have the capacity to hold thermal energy for a longer time. • Soup • Toast • Example: it takes longer for a pot of water to boil than it takes an iron to heat up. • Different materials require more thermal energy to heat them up.

23. In other words… • ….depending on the substance, it takes more energy to get the molecules to move. • Water is a liquid, molecules move more freely, while in a solid, the molecules are stuck together.

24. Definition of Specific Heat • The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 degree. • Specific heat is related to the resistance to change temperature. • Water has a very high specific heat capacity. • It takes a long time to heat up, and a lot of time to cool down.

25. Homework • RQ 13-16 pg 148 & 149

26. Organize your Thoughts! • Many terms in this chapter relate to each other. Create a graphic organizer (including definitions or pictures and real-life examples of each) with the following terms: • Temperature • 3 Laws of Thermodynamics • Thermal Energy • Heat • Cold • Specific Heat • Thermal Expansion