15 Temperature, Heat, Expansion

1. 15 Temperature, Heat, Expansion • Temperature & Heat • Internal Energy & Specific Heat • Homework: • RQ: 1, 2, 7, 8, 10, 12, 15, 21, 24.

2. Temperature • T ~ • Ex: hammered metal • Expansion with T increase

3. Superheating • Mythbusters • Instant coffee

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

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 the cold air in refrigerator • //

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 = D(Internal Energy)

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)

9. Calories and Joules • 1 Calorie = _______ calories • 1 calorie = ________ joule • Calorie is the common food unit. • Btu’s are also used, e.g. gas range

10. Specific Heat • quantity of heat required to raise the temperature of 1kg by 1°C. //

11. specific heat • c = Q/(mDT) [J/(kg·K)] • c = heat/(massx temperature change) • Water: 4186 J/kgC • heat needed per kg to raise temperature by 1 degree C or K.

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