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How hot or cold something is Measures avg. K.E. of the particles in the object. Tool: thermometer – meas. in degrees. Scales ~ Celsius (°C) 0° - 100° ~

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Presentation on theme: "How hot or cold something is Measures avg. K.E. of the particles in the object. Tool: thermometer – meas. in degrees. Scales ~ Celsius (°C) 0° - 100° ~"— Presentation transcript:

1 How hot or cold something is Measures avg. K.E. of the particles in the object. Tool: thermometer – meas. in degrees. Scales ~ Celsius (°C) 0° - 100° ~ Fahrenheit (°F) 32° - 212° ~ Kelvin (K) 273 K – 373 K 0 K – Absolute zero Temperature

2 Temperature Scales

3 Grand total KE & PE inside a substance. Depends on temp & amount of substance. Which beaker has more internal energy? Why? Internal Energy

4 Amount of internal energy required to change temp. A substance does not contain heat – it contains internal energy. Heat

5 Thermal Contact – objects in contact or mixed. Heat flows from higher temp. substance to low temp. substance. Thermal Equilibrium – thermal contacts reach same temp. – no heat flow. –Q lost = Q gained –There is no net change in energy! Energy is conserved! Heat

6 The internal energy changes when heat flows into or out of objects. Q = mct –Q = heat transferred (calories or joules) –m = mass (g) –C = specific heat (cal/g-°C) or (J/g-°C) –t = change in temp. (°C) Changes in Heat

7 Ability of a sub. to store internal energy. The amount of heat needed to raise the temp. of 1 g of the material 1 °C. Units: cal/g-°C. Specific Heat of Materials SubstanceSpecific Heat (cal/g-°C) Water1.00 Wood.42 Aluminum.22 Glass.16 Iron.11 Copper.09 Silver.06 Specific Heat Capacity or J/g-°C

8 calorie - the amount of heat needed to raise the temperature of 1 g water 1 °C. Kilocalorie = Calorie (food unit). –1 Kcal = 1000 calories Joule J = 1 calorie. Units of Heat

9 How much energy would it take for 1 kg of aluminum to change from 22 °C to 32 °C? Q = mct Q = 1000 g ·.216 cal/g-C · 10 ° C Q = 2,160 calories Calculate Heat Transferred

10 Lets compute how much energy it takes to make a cup of coffee or tea. Eight ounces of water has a mass of 0.22 kg. How much heat must be transferred to water to raise its temperature from 20 °C to 100 °C? Q = mct Q = 220 g · 1 cal/g-C · 80 ° C Q = 17,600 calories Calculate Heat Transferred

11 A 50 g piece of metal immersed in boiling water is placed in 100 g of water at 20 °C. The final temperature of metal and water is 28 °C. What is the specific heat of the metal? What is the metal? Q L = Q G mct = mct Methods of Mixtures (50g)(c)(72 °C) = (100 g)(1.0cal/g ·°C)(8 °C) c =.22 cal/g ·°C aluminum

12 A 50.0 g block of iron at 80 C is dropped into a cup of 200 g of water at 22 C. The block cools to 40 C. What would be the temperature change of the water? Q L = Q G mct = mct Methods of Mixtures (50 g)(.11 cal/g·°C)(40°C)=(200g)( 1cal/g°C)(T) T = 1.1 °C 22 °C °C = 23.1 °C is T f

13 Jerry grabs a hot g brass spoon from his bowl of soup, originally at a temperature of 95.0 C. To avoid burning his fingers he drops the spoon into a sink of 1,250 g water at 18.0 C. One second later, the spoon has cooled to a temperature of 75.0 C. Calculate the temperature of the water at this time. Q L = Q G mct = mct Methods of Mixtures (350 g) (.09 cal/g·°C) (20°C) = (1250g) ( 1cal/g°C) (T) T =.504 °C 18 °C °C = °C is T f

14 Mechanical Energy Relates to motion Potential Energy = mgd Kinetic Energy = ½mv 2 Work = F x d W = PE = KE Unit: Joule (J)

15 Thermal Energy Relates to motion of molecules Q = mc t Unit: calorie or Joules

16 Conservation of Energy Energy cant be created or destroyed, but can change forms, including between thermal and mechanical. E lost = E gain Q lost = Q gain KE = Q gain PE = Q gain W = Q gain

17 Mechanical Equivalent of Heat Relationship of mechanical energy to thermal energy. W = PE = KE = Q 1 calorie = J

18 A 5 kg concrete block falls 10 m to the ground. If all of the blocks energy is converted into heat that is absorbed by the block only, its temperature is raised _____? PE = Q mgd = mc t Mechanical – Thermal Energy 5 kg · 9.8 m/s 2 · 10 m = 5 kg · 670 J/kg-°C · t t = 0.15 °C

19 Expansion of a substance due to heat. Thermal Expansion

20 heat energy - kinetic energy - motion. Gas/Liquid/Solid – temperature – expand – temperature – contract Phase Expansion

21 As the temp. decreases from 4°C to 0°C, water expands - ice. –Its density decreases. The maximum density of water (1.0 g/mL) occurs at 4°C. Thermal Exp. of Water

22 Thermometer Sidewalk joints Building materials Thermostat – bimetallic strip Consequences?? Uses of Thermal Exp.

23 Different materials expand at different amounts with the same temperature rise. Thermal Coefficients for Length & Volume. –Solids (length) L = L O x x T Expansion Rates L = change in length L 0 = original length = coefficient of linear expansion T = change in temperature

24 Linear Expansion Coefficients Material Coefficient ( C –1 ) Aluminum 23 x Brass 19 x Copper 16 x Glass 3.2 x Gold 14 x Iron (Soft) 12 x Lead 29 x Quartz.40 x Steel 11 x 10 -6

25 Expansion Rates The Eiffel Tower, constructed in 1889 by Alexandre Eiffel, is an impressive latticework structure made of steel. If the tower is 301 m high on a 22 o C day, how much does its height decrease when the temperature cools to 0.0 o C? L = L O x x T = 301 m 10.5 x °C =.070 m


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