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Thermal Energy

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Thermal Energy

  1. 1. Thermal Energy<br />Ch. 9<br />
  2. 2. Thermal energyis the total energy of all the atoms and molecules in a substance.<br />The faster the molecules move, the more kinetic, and thus, thermal energy the substance has.<br />
  3. 3. Temperature is the average kinetic energy per molecule in a substance.<br />A substance with a high temperature also has molecules that are moving faster.<br />
  4. 4. Concept Check<br />Which has a higher temperature: a small cup of 140⁰F coffee or a large hot tub of 104⁰F water? <br />Which has more thermal energy?<br />
  5. 5. Absolute zero (0 kelvin, or 0 K) is nature’s lowest possible temperature, when molecules have no kinetic energy, and stop moving, a theoretical value, not yet observed. <br />0 K = -273°C<br />Water freezes at 0°C, and 273 K.<br />Water boils at 100°C and 373 K.<br />
  6. 6. Heat is the movement of thermal energy from one substance to another because of a difference in their temperatures.<br />When the two substances in contact with each other reach the same temperature, they are said to be in thermal equilibrium.<br />
  7. 7. Concept Check<br />When you touch a glass of ice water, does cold travel from the glass to your hand or does thermal energy travel as heat from your hand to the glass?<br />
  8. 8. Heat units are energy units, measured in joules or calories.<br />A calorie (cal) is the amount of heat needed to change the temperature of 1 gram, or mL, of water by 1 degree Celsius.<br />1 cal = 4.18 joules<br />The energy in food is measured by the unit Calorie and is 1000 calories, or kcal.<br />
  9. 9. :The Laws of Thermodynamics<br />1. When thermal energy transfers as heat, there is no net gain or loss. (i.e., Conservation of Energy)<br />2. The direction of heat flow is from warmer substances to colder substances.<br />3. No substance can reach absolute zero.<br />
  10. 10. Specific heat capacity is a measure of thermal inertia, how much thermal energy a substance needs to gain or lose to change its temperature by one degree.<br />
  11. 11. Concept Check<br />Which has a higher specific heat capacity: water or sand? (In other words, which takes longer to get warm in sunlight or cool at night)<br />
  12. 12. Thermal expansion is the spreading out of molecules as they heat up and move faster.<br />Different substances have different rates of thermal expansion.<br />Water is unusual because as it freezes the ice crystals spread out making ice less dense than liquid water. Water is most dense (compact) at 4°C.<br />

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