Chapter 16

1. Chapter 16 Thermal Energy and Heat

2. 16.1 Thermal Energy & Matter • Work and Heat • Heat- the transfer of thermal energy from one object to another because of a temperature difference  • Heat flows from higher temperatures to lower temperatures. • Temperature is related to the average kinetic energy of the particles in an object due to their random motion through space. • Collisions between particles transfer thermal energy from hot objects to cold objects.

3. Thermal Energy Thermal energy depends on mass and temperature. A The tea is at a higher temperature than the lemonade because its particles have a higher average kinetic energy. B The lemonade is at a lower temperature, but it has more thermal energy because it has many more particles. • Thermal Energy- Total PE and KE of all particles in an object. • Depends on: mass, temperature, and phase .

4. Thermal Contraction & Expansion • Thermal Expansion- an increase in the volume of a material due to a temperature increase. • Remember Charles’s Law? • As temperature increases, volume increases. • particles speed up, they have more collisions, and produce more collisions, and produce more force. • thermal expansion/contraction are used in thermometers.

5. Specific Heat Specific heat is the heat needed to raise the temperature of 1 gram of material by 1°C. Specific Heat- the amount of heat needed to raise the temperature of 1 gram of a material by 1ºC. The lower the specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass. Specific heat is measured in joules per gram per degree Celsius

6. Formula for Specific Heat Q = mc ΔT Q = heat absorbed by the material m = mass c = specific heat ΔT = change in temperature Ex: An iron skillet has a mass of 500 g. The specific heat = 0.449 J/g ·ºC. How much heat must be absorbed to raise the temperature by 95 ºC?

7. Math Practice 1.How much heat is needed to raise the temperature of 100.0 g of water by 85.0°C? 2.How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C? 3.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.) 4.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?5.What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

8. Measuring Heat Changes A sample to be tested is heated and placed in the calorimeter. The lid is put on and the temperature change is observed. • Calorimeter- an instrument 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

9. 16.2 Heat & Thermodynamics • There are three ways heat can be transferred. • 1. Conduction- The transfer of thermal energy with no overall transfer of matter. • Conduction can occur within a material or between materials that are touching. • Ex: Newton’s Cradle

10. The arrows show how thermal energy is conducted away from the heat source in a metal frying pan. • Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often. • In metals, conduction is faster due to the “sea of electrons” • Thermal Conductor- A material that conducts thermal energy well. • Ex: wire racks, copper, aluminum.

11. A thermal conductor does not have to be hot. Tile floors feel colder than wood floors even though they are at the same temperature. Tile floors feel colder because it is a better conductor. (It rapidly pulls the heat away from your foot.) • Thermal Insulator- A material that conducts energy poorly. • Ex: Wood and air. (double paned windows have a pocket of air.)

12. A Passing sandbags along a line is like transferring thermal energy by convection. B The arrows show convection of air in an oven. • 2. Convection- The transfer of thermal energy when particles of a fluid move from one place to another.  • Convection Current- Occurs when a fluid circulates in a loop as it alternately heats up and cools down. • As air heats up, it expands and rises. As it rises, it begins to cool. As it cools, it condenses and sinks.

13. A heating coil on a stove radiates thermal energy. The changing color of the red arrows indicates that the farther you are from the coil, the less radiation you receive • 3. Radiation-The transfer of energy by waves moving through space. Ex: Heat lamps used in restaurants. • All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases. • When you go to the beach, heat from the sun warms you by radiation.

14. Thermodynamics • Thermodynamics- The study of conversions between thermal energy and other forms of energy. There are three laws. • 1st Law of Thermodynamics • The first law of thermodynamics states that energy is conserved. (Remember the law of conservation of energy?)

15. Thermodynamics • 2nd Law of Thermodynamics • The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system.  • This is how refrigerators work. Remember, heat is supposed to flow from hot to cold. A refrigerator has to work hard to oppose this. • Heat Engine- any device that converts heat into work. • Waste Heat- thermal energy that is not converted into work. (lost to friction)

16. Thermodynamics This physicist is adjusting a laser used to cool rubidium atoms to 3 billionths of a kelvin above absolute zero. This record low temperature was produced by a team of scientists at the National Institute of Standards and Technology • 3rd Law of Thermodynamics • The third law of thermodynamics states that absolute zero cannot be reached.