Temperature and Heat

1. Temperature and Heat Chapter 12

2. Temperature • Temperature measures how hot or cold something is. • Temperature is related to the average kinetic energy of the particles (atoms or molecules). • Hot particles move faster.Cold particles move slower.

3. Temperature scales Temperatures are reported in degrees Celsius (°C) or degrees Fahrenheit (°F). Temperature changes are reported in Celsius degrees (C°) or Fahrenheit degrees (F°).

4. -40°F -40°C Temperature scales °F to °C conversion °C to °F conversion

5. Absolute temperature scale Kelvin is the SI unit for temperature Zero kelvin (0 K) is absolute zero SI temperatures are in kelvins, not degrees kelvin.

6. Thermocouple junction Thermometer Any property of a material that varies with temperature can be used to measure temperature. For example: A thermocouple junction generates different voltages at different temperatures. A thermocouple junction is a junction between two different kinds of wire.

7. temperature change change in length original length Linear expansion Lengths increase as an object heats up. Length changes by a fixed fraction (or percent) for each degree of temperature change. Fractional change for one degree is called the coefficient of linear expansion α.

8. coefficient of themal expansion unit:

9. Example 3 Buckling Sidewalk Find y for 13°C temperature rise.

10. A turn-signal relay uses thermal expansion to flash your turn-signal lights. http://auto.howstuffworks.com/turn-signal2.htm

11. Bimetallic strip Two materials with different thermal expansion rates that are bonded together. αbrass = 19 x 10-6 (C°)-1 αsteel = 12 x 10-6 (C°)-1

12. Thermostats use bimetallic strips Bimetallic strip

13. Conceptual Example 5 Expansion of holes A hole in a piece of solid material expands when heated and contracts when cooled just as if it were filled with material.

14. expanding coolant is stored in the reservoir temperature change change in volume original volume Volume expansion Volumes increase as an object heats up. Volume changes by a fixed fraction (or percent) for each degree of temperature change. Fractional change for one degree is called the coefficient of volume expansion β.

15. Volume expansion of water near freezing Most liquids solidify (freeze) upward from the bottom. Water freezes at the top surface because below 4°C water expands and floats upward.

16. hot Other heat units 1 cal = 4.186 joules 1 kcal = 4186 joules cold (1 food calorie) Heat Heat is thermal energy that is transferred from a hotter object to a cooler object because the objects are at different temperatures. Heat (thermal energy) is measured in joules (J). Q is the quantity of heat transferred.

17. Calorimeter An insulated container that prevents heat transfer between the sample and the environment. Lossless transfer of heat energy from the hotter material to the cooler material. Heat energy lost by the hotter material equals the heat energy gained by the cooler material.

18. sublimation gas ↔ solid vaporization gas ↔ liquid fusionsolid ↔ liquid Three phases of matter: solid, liquid, and gas Phase changes happen at specific temperatures.

19. Water Only steam Water and steam mixture Only water Water and ice mixture Only ice Heat transferred (J) Three phases of matter: solid, liquid, and gas Temperature of a mixture of two phases stays the same while heat energy is added or removed.

20. Latent heatMass that changes phase SI Units of Latent Heat: Heat transfer can cause a phase change Heat Q must be transferred into or out of the material to cause a phase change. Heat needed to change the phase of 1 kg of material is called the material's latent heat L for that phase change. Temperature remains constant during a phase change. Latent means not active as in “the temperature is not actively changing”.

21. Fusion is the freezing melting phase change. Vaporization is the evaporating condensing phase change. Latent heat values

22. Unit for specific heat capacity: Heat transfer can cause a temperature change If a material is not at a phase change temperature, heat transfer causes the temperature to change. Heat needed to change the temperature of 1 kg of material by 1°C is called the specific heat capacity. Temperature change Specific heat capacity c Mass of the material

23. Specific heat capacity values

24. Problem solving strategy While a material stays in the same phase Use Q = mcΔT for that material While a material is changing phase Use Q = mL for that material The total amount of heat added to the cool things always equals the total amount of heat lost by the hot things. For equilibrium situations, everything ends up at the same temperature.

25. Only steam Water and steam mixture Only water Water and ice mixture Only ice Problem solving strategy For situations that start in one phase and end in another phase, analyze the phase changes and temperature changes separately to calculate the total heat energy transferred.

26. Equilibrium example with no phase changes A 1 kg block of 120°C copper is dropped into 2 kg of 20°C water. Find the equilibrium temperature. Beginning assumption: no phase changes occur. Assume lossless heat transfer Copper cools Water warms The water didn’t reach the boiling point so not phase change occurred. ☺

27. Check the answer to verify that ☺ Equilibrium example with no phase changes

28. Equilibrium example with a phase change Example 14 Ice-cold Lemonade Ice at 0oC is placed in a Styrofoam cup containing 0.32 kg of lemonade (mostly water) at 27oC. Some ice still remains after the ice and lemonade reach an equilibrium temperature. How much ice melted to cool down the lemonade? Assume lossless heat transfer Since some ice remains so the final temperature is 0°C. The ices stays at 0°C while some of it melts. Q=mL The lemonade water cools from 27°C to 0°C. Q=mcΔT

29. ☺ Equilibrium example with a phase change Verify that the answer is correct (within round-off accuracy)

30. The End