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Measuring Heat

Measuring Heat. ,. Heating &. Cooling Systems. Ch 26 27 28. ,. ,. Temperature Scales and Thermal Energy. Temperature. Def . – A measure of average Kinetic Energy of the molecules in a substance. The higher the temperature, the faster the particles are moving!. Temp = KE.

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Measuring Heat

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  1. Measuring Heat , Heating & Cooling Systems Ch 26 27 28 , , .

  2. Temperature Scales and Thermal Energy

  3. Temperature Def. – A measure of average Kinetic Energy of the molecules in a substance The higher the temperature, the faster the particles are moving! Temp = KE

  4. Temperature Scales • There are three temperature scales: • Celsius (°C) • Fahrenheit (°F) • Kelvin (K) • On the Kelvin scale, there is a theoretical point called Absolute Zero where all molecular motion stops

  5. Comparison of Scales Copy in your notes!! Memorize it!!

  6. Thermal Energy Def: the Sum of kinetic and potential energies contained in a substance. • Takes into consideration temperatureandmass, and TOTALenergystored Temp = Thermal Energy Mass = Thermal Energy

  7. Temp & Thermal Energy • Each particle has about 10 J of energy in both objects. Which has the higher temp? Which has more thermal energy? Same Box 2

  8. HOT COLD Heat Movement When you open a door in summertime, hot air moves into the house. • Heat lost by one object is equal to heat gained by another. • First Law of Thermodynamics

  9. Thermal Equilibrium The amount of heat transfer depends on the initial temp. difference Note: heat will continue to flow until thermal equilibrium (same temp.)is reached This is why drinks get warm when left out

  10. Types of Heat Transfer

  11. Methods of Heat Transfer Three Methods: • Conduction • Convection • Radiation

  12. Heat Transfer 1. Conduction: transfer of heat by direct contact(TOUCH) Solids, liquids, & gases Ex. – Burning your hand on a hot stove

  13. Thermal Conductivity • Thermal Conductors: heat flows easily through these substances • Solids (i.e. – metals) are generally the best conductors • Thermal Insulators:Materials that decrease the transfer of heat. • Styrofoam, wood, plastic are examples of insulators

  14. Heat Transfer • Convection:transfer of heat by the motion of a fluid in the form of currents • Forced Convection: the process by which mechanical device moves a fluid or gas to transfer heat Liquids & gases ONLY Ex - weather, ocean currents, heating homes

  15. Heat Transfer 3. Radiation: transfer of heat OUTWARD by electromagnetic waves Ex – heat radiating from a fireplace

  16. TAKS

  17. TAKS Molten rock rises in Earth’s mantle and then sinks back toward the core in a circular pattern, as shown in the diagram. This method of heat transfer is known as — F conduction G vibration H radiation J convection

  18. Absorbers & Reflectors Absorbers: Absorb radiation easily & emit heat quickly Reflectors:Reflect radiation & emit heat slowly

  19. Heat Measurement & Specific Heat

  20. Joules • Calories and calories • BTU’s Measuring Heat The following are all commonly used units of measurement for Heat:

  21. Measuring Heat Since heat is a type of Energy Transfer, the standard unit for heat is the JOULE.

  22. Measuring Heat Typically used to measure the heat (energy) content in foods Calorie (kilocalorie): quantity of heat needed to raise temp. of 1g of water 1ºC. 1 C = 1000 c P. 446

  23. Btu: quantity of heat needed to raise 1lb. of water 1ºF. Btu British Thermal Unit Describes heat from heating systems

  24. Specific Heat (c) Def. - The amount of heat needed to raise the temperature of one gram of a substance one degree Celsius When thermal heat is transferred (flows) it raises the temp of some substances more than others!

  25. Specific Heat of Water Water is frequently used as a coolant because of its high specific heat. It takes: 1 calorie of Heat to raise the temp of 1 gram of H2O 1°C Equal to.. 4.186 joules of Heat to raise the temp of 1 gram of H2O1°C

  26. Weather Issues TAKS

  27. Calculating Heat

  28. Calculating Heat Change in Temp (ºC) Mass (g) Q = mC T Heat (Joules) Specific heat of a substance (J/g-ºC)

  29. Water c = 4.186 J/goC “It takes 4.186 J of energy to increase the temperature of 1 g of water 1 oC.” Air c = 1.005 J/goC “It takes 1.005 J of energy to increase the temperature of 1 g of air 1 oC.” What does “c” Mean? If equal amounts of heat were added to both air and water, which would have the greatest DT? Air!!

  30. Practice Problems Calculating Heat 1. An IPC student wants to raise the temperature of a 13g sample of copper from -30°C to 10°C. If the specific heat of copper is 0.385J/g-°C, how much heat needs to be added?

  31. Practice Problems Calculating Heat 2. A 50 g sample of a material required 60calories of heat to have its temperature raised from 20°C to 80°C. What is the specific heat of the material?

  32. Practice Problems Calculating Heat 3. A 200g sample of ethanol is provided with 1500J of heat energy. What will be the change in temperature of this sample if the specific heat is 2.44J/g-°C?

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