Thermodynamics

Brownian Motion  A large floating dust speck moves smoothly because it is much larger than a particle of water.  A tiny dust speck shows Brownian motion because of collisions with particles of water. 2

Key Question: What is temperature? Temperature and the Phases of Matter 3

 In the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees  The Celsius scale divides the difference between the freezing and boiling points of water into 100 degrees (instead of 180). Temperature and the Phases of Matter 4

Converting Temperatures  The A friend in Paris sends you a recipe for a cake.  The French recipe says to bake the cake at a temperature of 200°C for 45 minutes.  At what temperature should you set your oven, which reads temperature in Fahrenheit? 5

Temperature Scales  Three main scales FahrenheitCelsiusKelvin Water boils Water freezes Absolute Zero

 An increase in heat causes an expansion of the substance.  An example is a thermostat’s bimetallic strip.  In most liquids or solids, when temperature rises —molecules have more kinetic energy —consequently, things tend to expand (works for a gas) they are moving faster, on the average Thermal Expansion

Applications of Thermal Expansion – Bimetallic Strip  Thermostats —Use a bimetallic strip —Two metals expand differently Since they have different coefficients of expansion

 All thermometers are based on some physical property (such as color or volume) that changes with temperature.  A thermistor is a device that changes its electrical resistance as the temperature changes.  A thermocouple is another electrical sensor that measures temperature. Temperature and the Phases of Matter 9

 Temperature measures the kinetic energy per atom due to random motion.  Random motion is motion that is scattered equally in all directions.  In pure random motion the average change in position is zero. Temperature and the Phases of Matter 10

 When the temperature gets down to absolute zero, the atoms are said have the lowest energy they can have and the temperature cannot get any lower.  Technically, we believe atoms never stop moving completely.  Figuring out what happens when atoms are cooled to absolute zero is an area of active research. Temperature and the Phases of Matter 11

 The Kelvin temperature scale is useful for many scientific calculations because it starts at absolute zero.  The Kelvin scale is used because it measures the actual energy of atoms.  A temperature in Celsius measures only the relative energy, relative to zero Celsius. Temperature and the Phases of Matter 12

Phases of Matter  The three most common phases of matter are called solid, liquid, and gas.  At temperatures greater than 10,000 K the atoms in a gas start to break apart.  In the plasma state, matter becomes ionized. 13

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 When thermal energy is added or subtracted from a material, either the temperature changes, or the phase changes, but usually not both at the same time. Phases of Matter 15

Change from solid to liquid  The melting point is the temperature at which a material changes phase from solid to liquid.  Melting occurs when the kinetic energy of individual atoms equals the attractive force between atoms.  The heat of fusion is the amount of energy it takes to change one kilogram of material from solid to liquid or vice versa. 16

Energy and Heat of Fusion E = mh f Heat of Fusion (J/kg) Mass (kg) Heat energy (J) 17

Calculate Energy  How many joules does it take to melt a 30 gram ice cube at 0°C? 18

Evaporation  Evaporation occurs when molecules go from liquid to gas at temperatures below the boiling point.  Evaporation takes energy away from a liquid.  The average energy of the molecules left behind is lowered.  Evaporation cools the surface of a liquid because the fastest molecules escape and carry energy away. 19

Condensation  Condensation occurs when molecules go from gas to liquid at temperatures below the boiling point.  Condensation raises the temperature of a gas because atoms in a gas have more energy than atoms in a liquid.  When air is saturated, it means the processes of evaporation and condensation are exactly balanced. 20

Change from liquid to gas  The boiling point is the temperature at which the phase changes from liquid to gas.  Just as with melting, it takes energy for an atom to go from liquid to gas.  The heat of vaporization is the amount of energy it takes to convert one kilogram of liquid to one kilogram of gas. 21

Energy and Heat of Vaporization E = mh v Heat of Vaporization (J/kg) Mass (kg) Heat energy (J) 22

Calculate Energy  A steam iron is used to remove the wrinkles from clothes.  The iron boils water in a small chamber and vents steam out the bottom.  How much energy does it require to change one-half gram ( kg, or about half a teaspoon) of water into steam? 23

Heat and Thermal Energy  What is the relationship between heat, temperature, and energy? 24

 Temperature is NOT the same as thermal energy.  Thermal energy is energy stored in materials because of differences in temperature.  The thermal energy of an object is the total amount of random kinetic energy for all the atoms in the object.  Remember, temperature measures the random kinetic energy of each atom. Heat and Thermal Energy 25

 Imagine heating a cup of coffee to a temperature of 100°C.  Next think about heating up 1,000 cups of coffee to 100°C.  The final temperature is the same in both cases but the amount of energy needed is very different. Heat and Thermal Energy 26

 Heat is what we call thermal energy that is moving.  The joule (J) is the unit of heat (or thermal energy) used for physics and engineering.  The calorie is a unit of heat often used in chemistry. Heat flows from the hot coffee to the cooler air in the room. Heat and Thermal Energy 27

Specific Heat  The specific heat is the quantity of heat it takes to raise the temperature of one kilogram of material by one degree Celsius. 28

 The temperature of gold rises quickly compared with water because its specific heat is much less than the specific heat of water. Specific Heat 29

Heat Equation E = mc p (T 2 -T 1 ) Specific heat (J/kg o C) Mass (kg) Heat energy (J) Change in Temperature ( o C) 30

Calculate Heat  One kilogram of water is heated in a microwave oven that delivers 500 watts of heat to the water.  One watt is a flow of energy of one joule per second.  If the water starts at 10°C, how much time does it take to heat up to 100°C? 31

First Law of Thermodynamics Energy loss is equal to energy gain. 32

Second Law of Thermodynamics 33

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Application: The Refrigerator 35

Third Law - Entropy  Entropy is the measure of the amount of disorder.  As disorder increases, entropy increases.

Greenhouse Effect How do you keep the atmosphere from losing energy? A giant insulating pizza box?

100 units of energy on the wall...

Greenhouse Effect Carbon Dioxide, Water, Methane, Ozone and other greenhouse gases do not physically “block” energy transfer from occurring (like a greenhouse or pizza box). These gases absorb radiation, thus heating up, then, reradiate that energy (The atmosphere reaches a new equilibrium with the new chemical composition.)

Questions What is thermodynamics? A. The transfer of energy B. The transfer of heat C.The process of emitting energy D. The process of creating heat 41

Questions What is the difference between heat and internal energy? A. Heat flows from an area of high concentration to low B. Heat comes from microwaves C. Heat is the absence of cold D. Heat does not exist 42

Questions What are the different phase changes? A. Solid to liquid B. Liquid to solid C. Liquid to gas D. Solid to gas E. All of the above 43

Questions What is insulation? A. Process of releasing heat B. Process of delaying the transfer of heat C. Process of absorbing heat D. None of the above 44

Questions What is convection? A. Process of heating that occurs by the even flow of liquids and gases B. Cooking something in the oven C. Cooking something in the microwave D. None of the above 45

Questions What is the first law of thermodynamics? A. When heat is added to a system an equal amount is transferred B. When heat is added to a system an equal amount is conserved C. When heat is added to a system an equal amount is created D. When heat is added to a system an equal amount is destroyed 46

Questions What is the second law of thermodynamics? A. Heat flows from high to low temperature B. Heat does not flowing C. Heat is absent D. Heat flows fromlow to high temperature 47

Questions What is the third law of thermodynamics? A. The lowest temperature is absolute zero B. The highest temperature is infinity C. The lowest temperature is negative infinity D. The lowest temperature is -400 degrees celsius 48

Questions Who discovered the Third law? A. Mendel B. Newton C. Copernicus D. Dalton E. Einstein F. Faraday G. Galileo H. Nernst 49

Questions What is entropy? A. Measurement of disorder B. Measurement of destruction C. Measurement of order D. Measurement of natural selection 50

51 Questions As you heat a block of aluminum from 0 ° C to 100 ° C, its density (A) increases (B) decreases (C) stays the same

52 Questions An aluminum plate has a circular hole cut in it. A copper ball has exactly the same diameter as the hole when both are at room temperature, and hence can just barely be pushed through it. If both the plate and the ball are now heated up to a few hundred degrees Celsius, how will the ball and the hole fit ? (A) ball won’t fit (B) fits more easily (C) same as before

53 Questions Not being a great athlete, and having lots of money to spend, Gill Bates decides to keep the lake in his back yard at the exact temperature which will maximize the buoyant force on him when he swims. Which of the following would be the best choice? (A)0 o C (B) 4 o C (C) 32 o C (D) 100 o C (E) 212 o C