Chapter 6 Thermal Energy Section 1 Page 158-162. Temperature and Heat What do we observe about hot and cold? – Can we see hot? – We can compare hot and.

Chapter 6 Thermal Energy

Section 1Page 158-162

Temperature and Heat

• What do we observe about hot and cold?– Can we see hot?– We can compare hot and cold by touch.

• Hot and cold are subjective– For me, 72% is cold, for my wife it is hot– Swimming

• If a hot object and a cold object are placed side by side in an enclosed container, they come to the same temperature.

Temperature and Heat (cont)

• Hotter the temperature, the more heat• Heat can flow from a hot object to a cooler

object.• Early theory explained heat as a substance

called caloric– Does an object weigh more when it is hot?– Caloric therefore must be weightless

Particles in Constant Motion

Modern TheoryKinetic Theory of Heat Page 476

• Matter is made up of tiny particles, atoms and molecules

• These particles are in constant random motion– Move in all directions until they strike something

• Kinetic energy = ½ mv2

– More mass of the particle, more energy, more heat– Greater speed, more energy, more heat

• Potential energy– Particles attract each other so when separated they have

potential energy.

Heat/Thermal Energy

• Thermal Energy is the total kinetic and potential energy of the particles making up an object.

• Heat is thermal energy that flows from an object at a higher temperature to an object at a lower temperature.

• Heat always flows from higher temperature to lower temperature.

Temperature

• The temperature of an object is a measure of the average kinetic energy of the particles in an object.– Higher temperature, more kinetic energy– Lower temperature, less kinetic energy

• Temperature is measured by comparing characteristics of a substance that changes with temperature.– The volume of most substances change with

temperature

Thermometers

Fahrenheit

Celsius or centigrade Kelvin

Freezing temp of water

Boiling temp of water212o

100o 373o

32o 0o 273o

-273o 0o

Heat

• Heat is thermal energy that flows from an object at a higher temperature to an object at a lower temperature.

• Heat always flows from higher temperature to lower temperature.

• Since energy is conserved, heat that flows from one object must be gained by other objects.

Heat Quantity• At noon on the beach, how does the

temperature of the air, the water and the sand compare?

• The more heat that is added to an object, the higher the temperature rise.

• The amount of heat required to raise the temperature of an object depends on the material.

• The amount of heat (Joules) required to raise the temperature of 1 kg of material by 1oC is called the specific heat. (Page 161)

Quantity of Heat• Q = quantity of heat, measure in units of Joules• m= mass, measured in kilograms (kg)• Tf = final temperature, units of oC

• Ti = initial temperature, units of oC

• C = specific heat (c- used in most textbooks)• The quantity of heat required to raise the

temperature of 1 kilogram of substance by 1oC• The units are J/kg oC• Q = m (Tf - Ti )C or Q= mc ∆T

• ∆T = (Tf - Ti )

Specific Heats (P161)Substance Specific Heat (J/kg Co)

Aluminum 899Gold 129Concrete 880Copper 386Diamond 518Ethyl Alcohol 2400Glass 837Iron 447Water 4186

Definitions• Temperature – (measured with a thermometer) – a

measure of the average kinetic energy of the particles that make up an object.

• Thermal Energy – the sum of the kinetic and potential energy of the particles in an object.

• Heat – thermal energy that is transferred.• Specific heat – the amount of heat that is needed to

raise the temperature of 1 kg of a substance by 1 oC• Q = m (Tf - Ti )C or Q= mc ∆T

• The heat lost by one object must be gained by some other object.

Practice Problems p162: 1-3, P 163: 6,7

• A wooden block has a mass of 20.0 kg and specific heat of 1700 J/kg oC. Find the change in thermal energy of the block as it warms from 15 oC to 25 oC.

• Given• Asked?• Formula: Q = m (Tf - Ti )C or Q= mc ∆T


• The air in a living room has a mass of 60.0 kg and specific heat of 1020 J/kg oC. What is the change in thermal energy of the air when it warms from 20 oC to 25 oC.



• The thermal energy of water in a mug increases by 12,552 J when the water is heated from 20 oC to 40 oC. If the specific heat of water is 4,184 J/kg oC, what is the mass of the water?

• Given• Asked?• Formula:Q = m (Tf - Ti )C or Q= mc ∆T


• A block has a mass of 0.20 kg, a specific heat of 710 J/kg oC and is at a temperature of 20 oC. What is the block’s final temperature if its thermal energy increases by 2,130 J?



• Calculate the change in thermal energy of the water in a pond with a mass of 1,000 kg and a specific heat of 4,184 J/kg oC if the water cools by 1 oC.



• Calculate the specific heat of a metal if 0.5 kg of the metal absorbs 9,000 J of heat as it warms by 10 oC.


Chapter 6 Section 2Transferring Thermal Energy

Page 164-170

Transfer of Thermal Energy

• Conduction – thermal energy is transferred by the collision of particles with high kinetic energy with particles of lower kinetic energy.– Metals are good conductors

• Convection – the transfer of thermal energy in a fluid (liquid or gas) by the movement of warmer and cooler fluid from place to place

• Radiation- the transfer of thermal energy by electromagnetic waves (light, infra-red, ultraviolet, microwaves)

Controlling Thermal Energy Transfer

• Reflective surfaces reflect radiation and do not let the radiation pass.

• Vacuum prevents both convection and conduction.

• Air spaces prevents conduction.• Examples

– Attic insulation– Thermos bottle– Clothing

Calorimeter (page 163)

Vacuum Bottle

Chapter 6 Section 3Using Heat

Page 172-179

Definitions• Temperature – (measured with a thermometer) – a

measure of the average kinetic energy of the particles that make up an object.

• Thermal Energy – the sum of the kinetic and potential energy of the particles in an object.

• Heat – thermal energy that is transferred.• Specific heat – the amount of heat that is needed to

raise the temperature of 1 kg of a substance by 1 oC• Q = m (Tf - Ti )C or Q= mc ∆T

• The heat lost by one object must be gained by some other object.

Transfer of Thermal Energy

• Conduction – thermal energy is transferred by the collision of particles with high kinetic energy with particles of lower kinetic energy.– Metals are good conductors

• Convection – the transfer of thermal energy in a fluid (liquid or gas) by the movement of warmer and cooler fluid from place to place

• Radiation- the transfer of thermal energy by electromagnetic waves (light, infra-red, ultraviolet, microwaves)

Heating Systems• Source of Heat

– Burning Fuel (propane, fuel oil, coal, wood)– Electrical Resistance heating– Solar Heat – absorbing heat from sun light

• Transfer of Heat– Radiant Heat – old fashioned fireplace or stove– Force Air – Fan blows air through ducts and vents p172– Circulating Hot Water or Steam – pump and radiators– Heat pumps – as a gas expands it absorbs heat as it

contracts it gives off heat

Typical Forced Air

Solar Energy

• Passive solar – designing buildings to absorb and store heat directly from sunlight.– Orientation– South facing windows– Materials the store heat

• Active solar – systems that use sunlight to heat fluid (usually water) these fluids are then pumped to areas needing heat.

Passive Solar

Active Solar

Thermodynamics• Thermodynamics – movement of heat• Study of the relationships between work,

thermal energy and heat.• First Law of Thermodynamics

– In ordinary chemical and physical reactions, energy cannot be created nor destroyed.

– The increase in thermal energy of a system must equal the work done on the system and the heat transferred to the system

Laws of Thermodynamics• Second Law of Thermodynamics

– Energy always tends to go from a more usable form to a less usable form

– It is impossible for heat to flow from a cooler object to a warmer object unless work is done on the cooler object.

Converting Heat to WorkSteam Engines

• Steam engine uses fuel to heat water and turn it into steam.

• The steam is then used to push the blades of a turbine.

• Pushing the turbine uses up some of the energy of the steam and the steam condenses back to water.

Changing Heat to Work (cont)Internal combustion (p177)

• Internal combustion engine• Gasoline (or other fuel) vapors are mixed with

air.• Piston compresses the fuel/air mixture• Spark plug ignites the fuel/air mixture• The explosion produces hot gases (carbon

dioxide and carbon monoxide) which expand• Expanded gases push the piston down again.

Internal Combustion Engine

Converting Work to Heat (p175, 177)• Pushing the bicycle pump handle compresses

air.• Pushing the pump handle also generates heat.

– Friction of the pump– Compressing the air

• Friction from the parts of an automobile produce friction which generates heat.

• Heat is usually a wasted byproduct of work– Second Law of Thermodynamics

Refrigerator p178• Second Law of thermodynamics (Page 175)• It is impossible for heat to flow from a cool object

to a warm object unless work is done on the cool object.

• A refrigerator takes heat from the cold inside of the refrigerator and transfers it into the hot room.

• Impossible to move heat from a cold object to a warmer object unless we do work on the colder object.

Refrigerators and Heat Pumps• Special materials – freon• Freon changes to a gas at a low temperature if

the pressure is high.• Freon absorbs heat as it is changed into a gas.• The heat is absorbed from the surrounding air.• A pump (compressor) then compresses the

Freon and it turns back to a liquid, but in the process gives up heat.

• These two processes take place at low temperatures.

Refrigerators and Heat Pumps

Heat PumpRefrigerator or Heater

Heat Absorber

Heat Emitter

Compressor

Expansion Valve

compresses the freon and it turns back to a liquid, but in the process gives up heat.

Freon absorbs heat as it is changed into a gas.

Human Heating and Cooling

Human Coolant• Evaporation of a liquid to its gaseous form

(vapor) requires energy.• Evaporation of sweat on the body takes heat

energy from the body and uses this to convert the sweat to water vapor.

• Heat is conducted to the surface of the skin by blood vessels opening up to allow more blood flow.

• In cold weather, the blood vessels close down to prevent heat loss.

• We shiver to generate more heat.

Calorimeter (page 163)

Heat Transformed

• Energy (heat) is not created or destroyed. • Heat lost by the metal = heat gained by water

and cup• Heat lost = mmetal (Tf – Ti ) cmetal

• Heat gained= Qwater + Qcup

• Qwater = mwater (Tf – Ti ) cwater

• Qcup = mcuo (Tf – Ti ) ccup

Specific Heat of Metals

• Steel .490 J/g oC• Copper .390• Tin .210• Zinc .390• Silver .230• Gold .130

Chapter 6 Assignments• Thermal Energy Equation Problems

– Page 162: 1,2,3– Section Review Page 163 Applying Math #6, #7

• Specific Heat Lab• NTWS Chapter 6 Sections 1-2• Worksheet with Problems-• Worksheet Chapter 6 Section 3• Chapter 6 Review-Pages 184-185 11/28

– Questions 7,8,10, 12-15 , 23-25

• Chapter 6 Test 11/29

Q= m(Tf –Ti ) C

• 23. How much thermal energy is needed to raise the temperature of 4.0kg of water from 25o C to 75 oC?

• Given:• Asked:• Substitute: • Math:• Answer with units

Q= m(Tf –Ti ) C

• 24. How does the temperature of 33.0g of graphite change when it absorbs 350J of thermal energy?


Q= m(Tf –Ti ) C• 25. A hot iron ball is dropped into 200.0g of

cooler water. The water temperature increases by 2oC and the temperature of the ball decreases by 18.6oC. What is the mass of the iron ball?


Chapter 6 Thermal Energy Section 1 Page 158-162. Temperature and Heat What do we observe about hot and cold? – Can we see hot? – We can compare hot and.

Documents

higher temperature

heat thermal energy

initial temperature

temperaturethe temperature

final temperature

temperature rise

hot object

cold object