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Thermal Energy and Matter

Thermal Energy and Matter. Section 16.1. Hmmm…. Why aren’t machines 100% efficient? Where does that energy go? Why do most things generate heat?. FRICTION. How does heat flow? Quick lab. I will give you two different temperatures of water. They have the same volume

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Thermal Energy and Matter

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  1. Thermal Energy and Matter Section 16.1

  2. Hmmm… • Why aren’t machines 100% efficient? • Where does that energy go? • Why do most things generate heat? FRICTION

  3. How does heat flow? Quick lab • I will give you two different temperatures of water. They have the same volume • Find their initial temperatures • Mix them together in the Styrofoam cup • KEEP THE LID ON! • After 2 minutes, take the final temperature

  4. What is heat? • Heat is the transfer of thermal energy from one object to another • Heat flows spontaneously from hot objects to cold objects

  5. How is heat different from temperature? • Temperature is a measure of how hot or cold an object is compared to a reference point • Temperatures is really the average kinetic energy of particles in a substance

  6. How does heat flow? • Via collisions! • As molecules collide, energy can be transferred (high to low) • We’re looking at the AVERAGE amount of energy

  7. What was thermal energy again? • Total potential and kinetic energy of the particles of an object • Depends on… • Mass • Temperature • Phase (solid, liquid, gas, etc) or an object

  8. Which has more thermal energy? • Coffee or chocolate milk? • Why?

  9. Which has more thermal energy? • Glass or pitcher of lemonade? • Why?

  10. Which has more thermal energy? • Frozen ice pop or melted ice pop? • Why?

  11. Which has more thermal energy? • Cup of coffee or pitcher of lemonade? • Why?

  12. What’s happening here?

  13. Thermal Contraction and Expansion • As the temp drops, the particles… • Thermal contraction!

  14. Thermal Contraction and Expansion • As the temp raises, the particles… • Thermal expansion

  15. Specific Heat • Which part of this pan would you rather touch? Why?

  16. Specific heat • Specific heat is the amount of heat needed to raise one gram of a material 1° Celsius • So does the wood or the metal have a lower specific heat?

  17. Highest?

  18. Q = heat (J) • m = mass (g) • c = specific heat (J/g·°C ) • ΔT = change in temperature (°C)

  19. Problem • An iron skillet has a mass of 500.0 grams. The specific heat of iron is 0.449 J/g·°C. How much heat must be absorbed to raise the skillet's temperature by 95.0°C? • How much heat is needed to raise the temperature of 100.0 g of water by 85.0°C?

  20. Problem • How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C? • In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water's temperature? (Hint: Rearrange the specific heat formula to solve for ΔT.)

  21. To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of the silver increase? • What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

  22. How do we measure changes in heat?

  23. A calorimeter? • A calorimeter is a device used to measure changes in thermal energy • A calorimeter uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature. • These devices are sealed to prevent heat from escaping

  24. How is it used? • Have a mass of water at a certain temperature • Have an unknown item massed at a different temperature • Drop it in the water • Find the change in temperature of water

  25. Reviewing Concepts • In what direction does heat flow on its own? • How is the temperature of an object related to the average kinetic energy of its particles? • Name two variables that affect thermal energy. • What causes thermal expansion of an object when it is heated? • How do the temperature increases of different materials depend on their specific heats? • What principle explains how a calorimeter is used to measure the specific heat of a sample material?

  26. Heat and Thermodynamics Section 16.2

  27. Heat transfer • There are three different ways that thermal energy (heat) can transfer from substance to another • Conduction • Convection • Radiation

  28. Conduction • Conduction is the transfer of thermal energy with no overall transfer of matter • Within one substance • Between substances in contact • EX: Newton’s cradle • Solids v. liquids v. gases

  29. Which would you rather grab?

  30. Thermal conductors v. Insulators • Thermal conductors are materials that conduct thermal energy well • Metal • Tile • Thermal insulators are materials that conduct thermal energy poorly • Air • Wood • Wool • Styrofoam

  31. Convection • Convection is the transfer of thermal energy when particles of a fluid move from one place to another • Liquid or gas • Convection current happens when a fluid circulates in a loop as it heats and cools.

  32. Oceans, weather systems, magma in earth’s interior… …and food

  33. Radiation • Radiation is the transfer of energy by waves moving through space • Does not need matter to transfer through • Hotter something is, faster it radiates

  34. All together!

  35. Thermodynamics • Whole branch of science • Thermodynamics studies conversion between thermal energy and other forms of energy • Three supporting laws

  36. First Law of Thermodynamics • The first law of thermodynamics states that energy is conserved • Can’t create nor destroy • AKA law of conservation of energy

  37. Second Law of Thermodynamics • The second law of thermodynamics states that thermal energy can flow from cold to hot ONLY if work is done to the system • Natural flow pattern: warm objects to cold objects

  38. Heat engines and the second law • A heat engine is a device that converts heat into work • Will never be 100% because… • Energy not converted into work? Waste heat • Overall, disorder of universe is always increasing

  39. Third Law of Thermodynamics • The third law of thermodynamics states that absolute zero can never be reached • Molecules always moving somewhat…why efficiency can never be zero

  40. Facts about Absolute zero • The average temperature of the universe today is approximately 2.73 K • The current world record was set in 1999 at 100 picokelvins (pK), or 0.0000000001K, by cooling the nuclear spins in a piece of rhodium metal. • In February 2003, the Boomerang Nebula was observed to have the lowest natural temperature ever recorded (~1K)

  41. Reviewing Concepts • Why is conduction in gases slower than conduction in liquids or solids? • Give three examples of convection currents that occur in natural cycles • What happens to radiation from an object as its temperature increases? • State the first law of thermodynamics • In your own words, what is the second law of thermodynamics? • State the third law of thermodynamics

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