1. Heat and Temperature Light

2. The Nature of Matter All matter consists of tiny particles called molecules. These molecules are in a constant state of motion. –Molecules in liquids and gases move freely. –Molecules in solids simply vibrate. This means that all molecules possess their own kinetic energy (KE), the energy of motion. SolidLiquid/Gas

3. Temperature Look at the jar below. What do you notice about the speed of the molecules? –They move at different speeds. Now let’s add some heat. –Now they are all moving faster! Temperature relates to the average kinetic energy of the molecules in a substance. The higher the temperature, the faster the molecules move.

4. Temperature Scales There are three major temperature scales that we will deal with. –The Fahrenheit Scale (°F) –The Celsius Scale (°C) –The Kelvin Scale (K) Conversion formulas are shown below.

5. Sample Temperature Conversion A beaker of water at room temperature is measured to be at 21°C. What is the Fahrenheit and Kelvin temperature?

6. Special Temperatures There are several key temperatures that you will need to know in relation to the temperature scales. –The freezing point of water: –The boiling point of water: There are some other *special temperatures* that you may care to remember. –Body temperature:

7. Absolute Zero The final temperature to note is absolute zero, 0K. This is the lowest possible temperature. Here molecules are in a complete state of rest, which means that there is no kinetic energy. Absolute zero has never been reached. However, scientists have come within 0.1K 0K0K

8. Thermal Energy The sum of all the kinetic energies within a material is known as thermal energy. Both full cups of coffee are at the same temperature. –Which cup contains greater thermal energy? –Which cup contains a higher average kinetic energy within the molecules? A B B Both are the same!

9. What is Heat? Heat is energy in transfer from an object of higher temperature to one of lower temperature. In order for heat to be transferred, the objects must be in thermal contact. Eventually, they will reach the same temperature. This situation is called thermal equilibrium. ColdHot Heat Flow Warm

10. Heat Transfer Heat, being energy, is measured in Joules (J) The variable we will use for heat is Q. –If heat is gained, Q > 0 –If heat is lost, Q < 0 Heat transfer causes temperature change (  T). Every material has its own specific heat (c). This is the amount of heat required to raise 1kg of the substance by 1°C or 1K.

11. Common Specific Heat Capacities Recall, units are measured in Aluminum 903 Gold 129 Silver 233 Brass 377 Ice 2060 Steam 2020 Carbon 710 Iron 450 Water 4184 Copper 385 Lead 130 Zinc 388 Glass 664 Methanol 2450

12. Specific Heat Video Clip

13. Heat Equation The amount of heat required is proportional to mass (m), specific heat (c), and change in temperature (  T). The equation is shown below. Celsius and Kelvin are interchangeable here. Heat (J)Mass (kg) Temp Change (K or °C) Specific Heat

14. Sample Heat Problem How much heat is required to raise the temperature of a 2.4kg gold ingot (c = 129J/kgK) from 23°C to 45°C? 2.4kg Light

15. Sample Heat Problem 2 The ingot (m = 2.4kg) is then plunged into a bucket of cold water causing it to lose 9216J of heat. What is the temperature change (  T) of the ingot? If the ingot was initially at 45 ° C, then what is the final temperature? 2.4kg

16. Calorimetry Recall, all heat transfers require at least two substances, so simply calculating for one is not always enough. Recall, a heat transfer requires the objects to be at different temperatures. One always receives heat, while the other loses. –This occurs until thermal equilibrium is reached.

17. Calorimetry Equation The goal here is to find the final temperature when combining two substances of differing temperature.

18. Calorimetry Equation The equation applies to any number of substances by following the existing pattern.

19. Sample Problem (Calorimetry) A hot iron rod (T aI = 340°C) is dropped into a bucket of cold water (T bI = 10°C). If the mass of the rod is 0.5kg and the water 1.2kg, what is the final temperature of the mixture?

20. Heat Transfer Types Heat is transferred in three major ways: –Conduction –Convection –Radiation Again, heat only flows when there is a difference in temperature.

21. Conduction Conduction is the transfer of heat through molecular collisions. This form of heat transfer best occurs in solids where molecules are closely packed. Materials that conduct heat well are called conductors. (Eg. metals such as copper and iron) Materials that conduct heat poorly are called insulators. (Eg. foam, air, and asbestos) Magnification

22. Convection Convection is the transfer of heat through moving fluids. A fluid is any substance that flows, which includes all liquids and gases. Examples include convection ovens and cloud formation. Convection ?

23. Have you ever watched a pot of water when it is being heated, especially while boiling? What do you notice? You will notice that there are currents within the pot. The Heating Water Pot The process of convection transfers heated water from the bottom of the pot to the top, where it is exchanged for cooler water.

24. Radiation (not radioactivity) Radiation is the transfer of heat via electromagnetic waves. These waves include visible light, but are mostly infrared. No matter is required for this type of heat transfer. Examples include the sun’s heat and warmth felt from a flame. Open Space ? Radiation

25. More on Radiation All objects emit heat in the form of radiation (radiant heat). Hotter objects emit more energetic waves. Some extremely hot objects can emit visible light, a form of electromagnetic radiation. In fact, all forms of radiation travel at the speed of light. Objects in thermal equilibrium will emit the same amount of radiation that they receive from other objects.

26. Absorption and Emission Certain colored objects will absorb radiant heat better than others. Generally, objects of darker colors are these better absorbers.

27. Heat Transfer Question Consider a camp fire burning vigorously. –How is heat normally transferred while warming its viewers? Radiation –How is heat transferred when you put a hand in the smoke? Convection –How is heat transferred to a stick when it is placed in the hot coals? Conduction Some situations involve multiple heat transfer types like this.

28. The Thermos Bottle The Thermos® bottle is designed to effectively prevent heat loss/entry from affecting its contents. Conduction and convection are prevented by the vacuum between the two layers of glass. Radiation is minimized by the shiny metal that is on the unexposed side of each of the layers. Reflective Metal Vacuum Glass Some coffee pots contain this bottle.

29. Latent Heat (Enthalpy) As you know, an object requires a heat transfer (in/out) in order to have a temperature change (  T). A heat transfer is also required to change phase. Heat must be added to go to a more energetic phase. Heat must be removed to go to a less energetic phase. Solid Vapo r Liquid +Q -Q

30. Heats of Fusion and Vaporization The heat of fusion (H f ) is the amount of heat energy required change 1kg of substance in the solid state into the liquid state. The equation is as follows: The heat of vaporization (H v ) is the amount of heat energy required to change 1kg of substance in the liquid state into the vapor state. The equation is as follows:

31. Sample Heating Across Phase Consider a block of ice (m = 1.2kg) at -10°C being heated to water at 80°C. How much heat is used? –Consider the following process: These problems have 1-5 steps. Cooling uses negative numbers. Ice -10°CIce 0°CWater 0°C Water 80°C HeatingMeltingHeating

32. The Heating Curve (H 2 O) As H 2 O is heated from ice below freezing to steam above boiling, the temperature can be plotted with respect to time. What do you notice about the curve? Where are the flat spots located? What does this tell you about heating during a phase change? Temperature remains constant during phase changes. Once each phase change is complete, temperature can rise again. Heat HeatingMeltingBoiling Heat

33. The Cooling Curve (H 2 O) The cooling curve appears very similar to the heating curve, except for one very small difference. What is it? What can you conclude about temperatures when cooling between phases? SolidifyingCoolingCondensing Cooling also requires the temperature to be held constant while in the midst of a phase change. The temperature can continue to drop after all of the substance is converted into the next phase. Cool

34. Thermal Expansion Most substances expand when heated and contract when cooled. This property is known as thermal expansion. Thermal expansion applies to all phases (solid, liquid, and vapor.)

35. Linear Expansion of Solids As mentioned, solids expand upon heating. The change in length for a solid (  L) can be calculated, due to a linear relationship with temperature change (  T). The thermal expansion equation is shown below. The term , the coefficient of linear expansion is a value that depends on the material. Other helpful equations include: Change in Length (m)Initial Length (m) Coefficient of Linear Expansion (°C -1 ) Temperature Change (°C)

36. Sample Linear Expansion Problem A train rail is initially 20m long in the morning when the temperature outside is 10°C. By how much will the rail expand in the heat of the day when the temperature reaches 35°C? The coefficient of linear expansion for steel is: Now find  L. What is the final length?

37. The Bimetallic Strip A bimetallic strip consists of two metal strips pressed together into a single strip. A common strip consists of steel and brass. Since different materials expand at different rates, the strip will bend. Room Temp Brass Steel High Temp Brass Steel Low Temp Brass Steel

38. The Bimetallic Strip (Cont.) Bimetallic strips are most often used in temperature sensitive instruments as thermostats. The strip is wound into a coil. As temperature changes, the coil expands or contracts to activate a switch controlling a heating/cooling system. Heat AC I’m Hot!!! I’m Cold!!

39. Unique Properties of Water Like other substances, water expands and contracts when heated and cooled, except within a special range. However, water behaves strangely around its freezing point. Consider the graph shown below. Where does water appear most dense? What happens to water as it cools from 4°C to 0°C? What happens to water as it freezes into ice? What happens to ice as it cools below 0 ° C?

40. Unique Properties of Water (Cont.) In liquid water, the molecules move freely in no particular order or array. This is what allows them to flow. When water freezes, the molecules form a hexagonal pattern. Why may ice possess less density? O H H O HH O H H O H H O H H O H H O H H O H H O HH O H H O H H O H H O H H O H H O H H O H H O H H O HH Liquid Water O H H O HH O HH O H H O H H O H H Solid Ice O H H O HH O HH O H H O H H O H H O H H O HH O HH O H H O H H O H H Open Space

41. Applications of Linear Expansion Linear expansion must be taken into consideration for engineers designing something that will experience a range of temperatures. Here are just a few select examples: Can you think of any more? RailroadsBridgesMetal Roofs