May-14General Science Chapter 141 Heat and Temperature Chapter 14.
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Transcript of May-14General Science Chapter 141 Heat and Temperature Chapter 14.
04/10/23 General Science Chapter 14 1
Heat and Temperature
Chapter 14
04/10/23 General Science Chapter 14 2
Temperature
What do you know about temperature?Hot and cold can be used to describe
temperature.Heat is related to temperature, but they
are not the same thing.
04/10/23 General Science Chapter 14 3
Heat
The energy that flows from something with a higher temperature to something with a lower temperature.Always flows from warmer to cooler
Heat is measured in joules
04/10/23 General Science Chapter 14 4
Tiny moving particles
All matter is made up of tiny particles that are in constant motion. (Kinetic Theory)
The particles have kinetic energy.The faster they move, the more kinetic
energy they have.Temperature is a measure of the average
kinetic energy of the particles in a sample of matter.
04/10/23 General Science Chapter 14 5
Temperature
Which particles are moving faster, those in a hot cup of coffee or those in a bowl of ice cream?
The coffee – higher temperature means more kinetic energy, which means that the particles are moving faster
Temperature
We use thermometers to measure changes in temperatures.
Absolute Zero: Lowest temperature that an object can have (-273.15°C)
Common units for temperature areKelvin SI unitCelsiusFahrenheit
04/10/23 General Science Chapter 14 6
Temperature conversions
04/10/23 General Science Chapter 14 7
K = C + 273 C = K - 273
04/10/23 General Science Chapter 14 8
Heat and Phase Changes
Heat is the transfer of energy from a warmer temperature to a cooler temperature.
In some cases this temperature change will cause the substance to go through a phase change
04/10/23 General Science Chapter 14 9
Phase Changes
Solid to a liquid ---- MeltingLiquid to a gas ---- EvaporationGas to a liquid ---- CondensationLiquid to a solid ---- FreezingWhen sufficient heat is added or removed
from a substance (which slows or increases the motion of the particles) a phase change will occur
04/10/23 General Science Chapter 14 10
Phase Changes
The temperature at which the phase occurs is called the melting point or freezing point, etc.Melting point and Freezing point occur at the
same temperatureIt just depends on whether the substance is
gaining heat or losing heatTherefore evaporation point/boiling point and
condensation point occur at the same temperature
04/10/23 General Science Chapter 14 11
Heating curve for water
04/10/23 General Science Chapter 14 12
Heating Curve
Important information for the heating curveWhat is the independent variable?What is the dependent variable?Can you identify what phase a substance is in
when looking at the heating curve?Can you identify where phase changes occur
on the heating curve?
04/10/23 General Science Chapter 14 13
Discussion #1
Why do ice cubes melt when you put them in your drink?
What is absolute zero and what is the value of absolute zero?
What does temperature measure?What are the 3 temperature scales?
04/10/23 General Science Chapter 14 14
Discuss #1
What happens to molecules during a phase change?
Explain the parts of the heating curve.Explain what is happening on the constant
sloped lines on the heating curve.What is a phase change and what are 3
examples?
04/10/23 General Science Chapter 14 15
Conduction
The transfer of energy by direct contact of particles.
When particles collide, the faster moving one gives some of its energy to the slower moving one.
04/10/23 General Science Chapter 14 16
Conduction
Can transfer energy through a given material or from one material to another.Example: holding a metal spoon with one end
in boiling water.
Can take place in solids, liquids, or gases.Solids usually conduct heat better
particles are closer together
04/10/23 General Science Chapter 14 17
Conductors
Good heat conductors – materials that transfer heat easily.Metals
Poor heat conductors – don’t conduct heat easilyplasticwoodglassfiberglass
04/10/23 General Science Chapter 14 18
Reducing heat flow
Good heat insulators reduce the flow of heat.
They are bad heat conductorsGases such as airWoodPlasticGlassfiberglass
04/10/23 General Science Chapter 14 19
Air pockets
Many insulating materials make use of small pockets of air inside them. The pockets are too small to allow convection currents to form, so they are good insulators.Styrofoam coolersDown blanketsInsulation for your house
04/10/23 General Science Chapter 14 20
R-value
Resistance to heat flowHigher values mean it is a better insulator.You should use higher R-value materials
in roofs and ceilings because more heat escapes upward by convection currents.
04/10/23 General Science Chapter 14 21
Double-paned windows
Heat is lost through glass windows.By putting a thin layer of air between two
panes of glass gives a window a higher R-value.
High R-values keep heat inside in the winter and outside in the summer.
04/10/23 General Science Chapter 14 22
Thermoses
Also called vacuum bottles.Contain a double glass wall with a
vacuum in the middle to prevent heat transfer.
04/10/23 General Science Chapter 14 23
Fluid
Any material that can flow Liquid or gas
Air is a common example
04/10/23 General Science Chapter 14 24
Convection
The transfer of energy by the movement of matter
The particles move from one place to another, carrying the energy with them.
When a fluid is heated, the particles move faster. Since they can move, they do – and they spread out.
Fluids expand when heated.
04/10/23 General Science Chapter 14 25
Heating water
When the water at the bottom gets hot, it expands, and becomes less dense.
The cooler, more dense water above it sinks and pushes the warm water up.
As the water rises, it becomes cooler and more dense, and moves towards the bottom again.
04/10/23 General Science Chapter 14 26
Convection currents
This movement creates convection currents that transfer energy from warmer to cooler parts of the fluid.
04/10/23 General Science Chapter 14 27
Radiation
The transfer of energy in the form of invisible rays.
Does not require matter to be present.Radiant energy – energy that travels by
radiation
04/10/23 General Science Chapter 14 28
Energy from the sun
Radiant energyit travels through mostly empty space to reach
us.
Shiny materials reflect radiant energy, while dull materials absorb it.
Dark-colored materials absorb more radiant energy than light-colored materials.
04/10/23 General Science Chapter 14 29
Discussion #2
List the 3 types of heat transferWhat is a convection current?What is the difference between an
insulator and a conductor?List 3 insulators and 3 conductors.What does an R-value tell us?What is the advantage of a double pane
window?
04/10/23 General Science Chapter 14 30
Discuss #2
What is conduction?What is radiation?What is convection?Why do birds fluff their feathers and
mammals fluff their fur to keep warm?
04/10/23 General Science Chapter 14 31
Specific Heat
Different materials require different amounts of energy to produce the same temperature change.
The specific heat (Cp) of a material is the amount of energy it takes to raise the temperature of 1 kg of the material 1 degree Celsius.
Units are J/kg∙°CAlso called heat capacity
04/10/23 General Science Chapter 14 32
Specific heat
Water has a high specific heat, so it takes a lot of energy to raise its temperature.
That’s why the temperature of a lake or unheated swimming pool is always cooler than the temperature of the air around it.
04/10/23 General Science Chapter 14 33
Using Specific heat
We can’t measure change in thermal energy directly.
However, we can measure the change in temperature and use the specific heat to calculate the change in thermal energy.
04/10/23 General Science Chapter 14 34
Change in Thermal Energy
€
change in
thermal energy= mass( ) ×
specific
heat
⎛
⎝ ⎜
⎞
⎠ ⎟×
change in
temp.
⎛
⎝ ⎜
⎞
⎠ ⎟
€
Q = m ×Cp × ΔT
04/10/23 General Science Chapter 14 35
Delta
The Greek letter (delta) means “change in”T means change in temperatureAlways take final temperature minus initial
temperature.When T is positive, the object has increased in
temperature and taken in heat.When T is negative, the object has decreased
in temperature and given off heat.
04/10/23 General Science Chapter 14 36
Example
Calculate the thermal energy change when 230 g of water warms from 12 °C to 90 °C.
Q = m∙Cp∙T
Q = (0.230 kg)(4184J/kg∙°C)(90 °C – 12 °C)Q = (0.230 kg)(4184 J/kg∙°C )(78 °C)Q = 75061 J
04/10/23 General Science Chapter 14 37
You try
A 3.1 kg block of aluminum cools from 35°C to 20 °C. What is the change in its thermal energy?
Q = (3.1 kg)(-15 °C)(920 J/kg∙°C)Q= - 42780 J
04/10/23 General Science Chapter 14 38
Discussion #3
What do each of the symbols in the equation Q = m∙Cp∙T stand for?
What substance has the larger specific heat? Water or Aluminum
Would 750 grams of Iron (Cp = 500) or 750 grams of Zinc (Cp = 800) require more energy to warm up? Explain
Would your answer above change if the substances were cooling down? Why?
04/10/23 General Science Chapter 14 39
Stoves or fireplaces
Simplest heating systemsFuel is burned in the area to be heatedHeat transferred to surrounding air by
conduction, convection, and radiation.
04/10/23 General Science Chapter 14 40
Radiator
Device with a large surface areaHeats surrounding air by conductionConvection currents carry warm air
throughout the room.
04/10/23 General Science Chapter 14 41
Radiator (Hot water or Steam)
A fuel is burned to heat water.The hot water travels through pipes to the
radiator.Or, the water is boiled and the steam travels
through the pipes
The cooled water or steam returns to the furnace to heat again.
04/10/23 General Science Chapter 14 42
Forced air
Fuel is burned to heat air.A blower forces the warm air into a room.Convection currents carry the warm air
throughout the room.Cool air returns to the furnace to heat
again.
04/10/23 General Science Chapter 14 43
Radiant Heat (electric or water)
Heating coils in the floor or ceiling are heated by electricity or with water.
Nearby air is heated by conduction.Materials in the room are heated by
radiation.
04/10/23 General Science Chapter 14 44
Radiant Energy Examples
Pictures from Zach Wiltse
04/10/23 General Science Chapter 14 45
Heat Pump
Heat energy is collected with a network of coiled pipes on the outside of the home.
Heat from the ground evaporates a liquid inside the coils.
The vapor moves to a condenser which increases the pressure to increase the temperature of the vapor further.
04/10/23 General Science Chapter 14 46
Heat Pump
The heated vapor warms the surrounding air.
The heated air is moved through the building with a blower, similar to a forced air system.
As the vapor cools, it condenses to a liquid and is returned to network of pipes on the outside of the home to repeat the process
04/10/23 General Science Chapter 14 47
Geothermal picture
04/10/23 General Science Chapter 14 48
Heat Pump
04/10/23 General Science Chapter 14 49
Solar Heating
Uses energy from the sun.Two kinds of solar heating
passiveactive
04/10/23 General Science Chapter 14 50
Passive solar heating
Windows allow solar energy in.It is absorbed as thermal energy by
materials in the room.Later, it is released to the room.
04/10/23 General Science Chapter 14 51
Active solar heating
Collectors on the roof or the south side of the building. (solar collectors)
Energy is absorbed by liquid in pipes in collectors.
Heated liquid runs through house to radiators.
Cooled liquid returns to collectors
04/10/23 General Science Chapter 14 52
Discussion #4
List the 5 main types of central heating systems.
What are the 2 types of solar heating?What is the difference between the 2
types of solar heating?
04/10/23 General Science Chapter 14 53
Discuss #4
What types of heating systems heat by conduction?
What types of heating systems heat by convection?
What types of heating systems heat by radiation?
04/10/23 General Science Chapter 14 54
Thermal Expansion
An increase in volume of a substance due to a change in the substances temperature
As materials heat up the particles begin to move faster, this makes them spread apart slightly in all directions.Freezing water, thermostat, an inner tube on a
bicycle tire
04/10/23 General Science Chapter 14 55
Thermal Expansion
Expansion jointsGaps that allow materials to expand and
contract with temperature changesMetal joints on bridgesSpaces with “tar” in sidewalks
04/10/23 General Science Chapter 14 56
Thermal Expansion Examples
Thermodynamics
1st Law of Thermodynamics: The net change in energy equals the energy transferred as work and heat
2nd Law of Thermodynamics: energy transferred as heat always moves from objects of high temperature to objects of low temperatures. The total disorder of a system will increase.
04/10/23 General Science Chapter 14 57
Entropy
Measure of the amount of disorder in a system.
Symbolized by the letter S.Higher temperature = more entropyLower temperature = less entropyGas > Liquid > Solid
04/10/23 General Science Chapter 14 58
04/10/23 General Science Chapter 14 59
Heat movers
If heat always flows from warmer to colder, how do refrigerators move the warm air from inside to the even warmer air outside?
Work must be doneThis work is powered by electricity.
04/10/23 General Science Chapter 14 60
Heat movers
Devices that remove thermal energy from one location and transfer it to another location at a different temperature.
04/10/23 General Science Chapter 14 61
Cooling systems (Fridge or AC)
Main purpose of a cooling system is to remove heat energy by use of refrigerantsThe refrigerant will gain heat energy from the
surrounding environment.The refrigerant begins in the liquid form causing
it to evaporate as it gains heat energy.The refrigerant then travels to a compressor to
remove the heat and condense back to a liquid and begin the process again.
04/10/23 General Science Chapter 14 62
Refrigerants
Cooling systems use refrigerants to help remove the heat energy. Chemicals used in cooling systems that usually
evaporate quickly at low temperatures.Air, water, ammonia and carbon dioxide are
common natural refrigerantsFreon is the most commonly used refrigerant,
because it is nontoxic, odorless, and non-corrosive.Freon is harmful to the environment
04/10/23 General Science Chapter 14 63
Other heat movers
Air conditioners – work like refrigerators, only they are designed to cool larger areas.
Heat pumps – work like air conditioners when it is warm out. When it is cold, they take thermal energy from the cold air outside and transfer it inside the house.
04/10/23 General Science Chapter 14 64
Your bodies cooling system
People normally sweat when they become warm.
Our body does this so the sweat evaporates by using the heat from our bodies.
The heat used from our body to evaporate the sweat makes our bodies feel cooler due to the transfer of heat.
04/10/23 General Science Chapter 14 65
Discussion #5
Before there were refrigerators, people had iceboxes.
Ice was placed on the top shelf of an insulated box, and food was placed on the shelves below it.
How did this work?
04/10/23 General Science Chapter 14 66
Discuss #5
What is a heat mover?List some examples of heat movers
04/10/23 General Science Chapter 14 67
Heating curve for Iron