Thermal Energy and Heat Chapter 16 Thermal Energy and Heat

Begin Chapter 16 Agenda Thermal Energy Thermal Expansion Specific Heat Math Measuring Heat

16.1 Thermal Energy & Matter Work and Heat Heat - the transfer of thermal energy from one object to another because of a temperature difference  Heat flows from higher temps to lower temps Temperature is related to the kinetic energy of the particles: particles move around as they heat Collisions between particles transfer thermal energy from hot objects to cold objects.

Thermal Energy Thermal Energy - Total PE and KE of all particles in an object Depends on: mass, temperature, and phase - Kinetic Thermal Energy – Energy from the moving particles - Potential Thermal Energy – Energy from the # of particles that could possible move Ex: Below: The lemonade has higher Potential Thermal Energy The tea has higher Kinetic Thermal Energy Thermal energy depends on mass and temperature. A The tea is at a higher temperature than the lemonade because its particles have a higher average kinetic energy. B The lemonade is at a lower temperature, but it has more thermal energy because it has many more particles.

Thermal Contraction & Expansion It turns out that objects get bigger or smaller based on heat! Thermal Expansion- the volume of a material increases when a temperature increases. Remember Charles’s Law? (As temperature increases, volume increases) Particles speed up, and have more collisions, and which makes even more collisions, and produce more force. Thermal expansion/contraction are used in lots of things! Thermometers, car tires, “Deflate-gate”

Specific Heat Specific Heat- aka “Heat Capacity” the amount of heat needed to raise the temperature of 1 gram of a material by 1ºC. The ability of a material to hold onto heat. The Higher the specific heat, the Better it can grab onto and hold heat. Specific Heat is measured in joules per gram per degree Celsius J g ºC Specific heat is the heat needed to raise the temperature of 1 gram of material by 1°C.

Formula for Specific Heat Q = mcΔT Q = heat absorbed by the material m = mass c = specific heat (different for every material) ΔT = change in temperature Ex: An iron skillet has a mass of 500 g. The specific heat = 0.449 J/g ·ºC. How much heat must be absorbed to raise the temperature by 95 ºC?

Math Practice 1. How much heat is needed to raise the temperature of 100.0 g of water by 85.0°C? 2. How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C?

Math Practice 3. In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water's temperature? (Hint: Rearrange the specific heat formula to solve for ΔT.) 4. To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by 23J. What is the final temperature if the ring starts at 80°C?

Math Practice 5. What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

How do we Measure Changes in Heat? Calorimeter- an instrument used to measure changes in thermal energy A calorimeter uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature A sample to be tested is heated and placed in the calorimeter. The lid is put on and the temperature change is observed.

Calorimeter Problem #1 A 320 g ball of iron metal is heated to 90 °C and placed in a calorimeter containing 10200g of water at 25°C. The metal and water were allowed to come to an equilibrium temperature .From the thermal energy gained by the water, determine the new temperature of the water. (Specific heat of water is 4.18 J/g·°C and Specific heat of brass is .45 J/g·°C.) Careful with units!

Calorimeter Problem #2 A 59.047 g piece of mystery metal was heated to 100.0 °C and then put it into 100.0 mL of water which is 23.7 °C. The metal and water were allowed to come to an equilibrium temperature, determined to be 27.8 °C. Assume no heat lost to the environment. Calculate the specific heat of the metal and then identify the metal. (Hint: First calculate the heat absorbed by the water then use this value for “Q” to determine the specific heat of the metal in a second calculation) Qwater= 1713.8 J Cmetal= 0.402 J/g oC

Warm Up Test Practice How much will the temperature of my 100g coin change if I apply 1950J of heat to it. The specific heat of my coins is .390J/g’C.

16.2 Heat & Thermodynamics 1. Conduction 2. Convection 3. Radiation There are three ways heat can be transferred. 1. Conduction 2. Convection 3. Radiation

16.2 Heat & Thermodynamics 1. Conduction- when thermal energy is transferred in an object with NO overall change in the matter of the object Conduction can occur within a material or between materials that are touching. Ex: a metal rod will eventually become hot where you are holding it...then heat transfers to your hand

Thermal Conductors/Insulators NOTE: Conduction in gases is slower than in liquids and solids because the particles in a gas are more spread out, and therefore collide less often. In metals, conduction is fastest due to the “sea of electrons” Thermal Conductor - A material that conducts thermal energy well. Ex: wire racks, copper, aluminum. The arrows show how thermal energy is conducted away from the heat source in a metal frying pan.

Thermal Conductors/Insulators Note about thermal conductors: A thermal conductor does not have to be hot. Ex: Tile floors feel colder than wood floors even though they are at the same temperature. Tile floors feel colder because it is a better conductor. (It rapidly pulls the heat away from your foot.) Thermal Insulator- A material that conducts energy poorly. Ex: Wood and air. (double paned windows have a pocket of air.)

2. Convection - transfer of thermal energy when particles of a fluid move from one place to another. Convection Current - Occurs when a fluid circulates in a loop as it alternately heats up and cools down. As air heats up, it expands and rises. As it rises, it begins to cool. As it cools, it condenses and sinks. Space Heater

3. Radiation - The transfer of energy by waves moving through space 3. Radiation - The transfer of energy by waves moving through space. No particles are involved Ex: Heat lamps used in restaurants. All objects radiate energy. As an object’s temperature increases, the rate at energy radiation increases also. EX: When you go to the beach, heat from the sun warms you by radiation.

Thermodynamics Thermodynamics - The study of how thermal energy converts between heat and other forms of energy. There are 3 laws: 1st, 2nd, 3rd

Thermodynamics 1st Law of Thermodynamics The first law of thermodynamics states that energy is conserved. (Remember the Law of Conservation of Energy?)

Thermodynamics 2nd Law of Thermodynamics Well…….. Recall earlier, we learned that heat flows from hotter to colder objects Well…….. Heat can ALSO flow from colder objects to hotter objects…but only if work is done on the system.   This is how refrigerators work: Remember: heat is supposed to flow from hot to cold. A refrigerator has to work hard to oppose this. Heat Engine- any device that converts heat into work. Waste Heat- thermal energy that is NOT converted into work. (lost to friction)

EX: Refrigerator Heat Engine In most cases, heat is transferred from hot things to cold things A Heat engine, such as a refrigerator, moves air from cold to warm… the warmest-cold air gets pumped out of the fridge

Thermodynamics Wait, What is absolute Zero again?? 3rd Law of Thermodynamics At Absolute Zero, all matter stops moving. PS: most scientist believe this temp. CANNOT be reached. Wait, What is absolute Zero again?? -273.15°C or 0 Kelvin A temperature so cold that ALL particles stop moving In other words, vibrating particles in solids stop vibrating BTW: This is where Kelvin comes from! This physicist is adjusting a laser used to cool rubidium atoms to 3 billionths of a kelvin above absolute zero. This record low temperature was produced by a team of scientists at the National Institute of Standards and Technology

4/30 Do Now: Explain the difference between radiation and convection Which Law of Thermodynamics law involves Absolute Zero? Explain how Fire can represent each of the 3 ways heat is transferred Explain how the 2nd Law of Thermodynamics involves Refrigerators

Test Practice A mystery metal object has a mass of 75g. After heating up the metal to 100°C, you placed the object into 150g of 25°C water in a new container. The specific heat of water is 4.18 J/g°C and the .661 J/g°C for the metal. What is the final temperature of the water?

From Packet l00.0 mL of 20°C water is heated by dropping in a 695g piece of hot brass metal at 90°C. The specific heat of water is 4.18 J/g°C. The specific heat of brass is 0.386 J/ g°C. What is the equilibrium temperature of the metal-water system? (Answer= 47.38 degrees C)

Test Practice 1. Which process heats the person’s hands directly above the fire? a. Conduction b. Convection c. Radiation 2. Which process heats the person’s hands to the side of the fire? a. Conduction b. Convection c. Radiation 3. Which process makes the end of the poker hot, so the person has to wear a glove? 4. Conduction is the process Where energy is transferred as electromagnetic waves Where energy is transferred through direct contact Where energy is transferred through indirect contact 5. Radiation is the process 6. Convection is the process

Test Practice What is a thermal conductor and a thermal insulator? Why is it warmer in the ocean water at night than in the day? Which law of thermodynamics explains how a car air conditioner works?

Test Practice How does Absolute Zero connect to the idea of Kinetic Theory of Matter Why do you put a jar of pickles under hot water to help you open it?

Calorimeter Problem #3 A 380 g cylinder of brass metal is heated to 100 °C and placed in a calorimeter containing 21500g of water at 25°C. From the thermal energy gained by the water, determine the final temperature of the water. (Specific heat of water is 4.18 J/g·°C and Specific heat of brass is .38 J/g·°C.)

4/15 Do Now: Which of the 3 ways that heat is transferred (conduction, convection, radiation) involves moving particles of matter? Explain the 2nd law of Thermodynamics How does Absolute Zero connect to the idea of Kinetic Theory of Matter

4/12 Do Now: What is a calorie? What is a calorimeter and how does it work? Why do you put a jar of pickles under hot water to help you open it?