1. 1 15 Temperature, Heat, Expansion Temperature & Heat Internal Energy & Specific Heat Homework: RQ: 1, 2, 7, 8, 9, 10, 15, 21, 24.

2. 2 Temperature T ~ average kinetic energy T increase = increase in speed of molecules, e.g. hammered metal increases in temperature. liquids, gases, and solids usually expand when T increased

3. 3 Water Expansion Water expands from 4°C to 100°C (as does most materials) However, water contracts when warmed from 0°C to 4°C. (transient ice melting)

4. 4

5. 5 What happens to the hole size?

6. 6 Heat ‘heat’ is a transfer of thermal energy due to temperature difference Examples: ice in warm liquid: heat flows from liquid to the ice warm liquid is put in a refrigerator: heat flows from drink to air and refrigerator //

7. 7 Internal Energy the total of all molecular energies, kinetic plus potential, that are internal to a substance. It is ~ (mass) x (temperature). Heat ≠ Internal Energy, however, for a thermal-only process, Heat =  (Internal Energy)

8. 8 mixing: ‘hot’ and ‘cold’ = ‘warm’ for liquids & solids: heat ~ (mass)x(temperature change) when ‘hot’ and ‘cold’ are mixed, heat lost by ‘hot’ = heat gained by ‘cold’ Ex. 1kg water at 0°C is mixed with 1kg water at 20°C: (1kg)(T - 0) = (1kg)(20 – T) T = 20 – T 2T = 20 T = 10°C

9. 9 more mixing Ex. 2kg water at 40°C is mixed with 1kg water at 20°C: (1kg)(T - 20) = (2kg)(40 – T) T – 20 = 80 – 2T 3T = 100 T = 100/3 = 33.3°C

10. 10 Calories and Joules 1 Calorie = 1000 calories 1 calorie = 4.18 joule Calorie is the common food unit. Btu’s are also used, e.g. gas range

11. 11 Specific Heat the specific heat of a substance is the quantity of heat required to raise the temperature of 1kg of a substance 1°C. //

12. 12 c = Q/m  T [J/(kg·K)] heat needed per kg to raise temperature by 1 degree C or K. slope warming water =  T/Q = 1/(mc) specific heat

13. 13 example c’s in J/(kg-C): aluminum 920 copper 390 ice 2100 water 4186

14. 14 Example: A student wants to check “c” for an unknown substance. She adds 230J of heat to 0.50kg of the substance. The temperature rises 4.0K.

15. 15 summary T ~ avg. KE most substances undergo thermal expansion (note the water exception) heat is an exchange of thermal energy specific heat = heat needed to raise temp. of 1kg by 1C (substance dependent)

16. 16 Thermodynamics flow and effect of thermal energy on matter (solids, liquids, gases) temperature and internal energy heat engines