1. Chapter 17: Understanding Heat Transfer, Conduction, Convection and Radiation

2. The Evolution of the Discovery of Heat
1798: Benjamin Thompson (Count Rumford) performed experiments to test how heat is produced.
He concluded that action or work produces heat.
He concluded that heat is a form of energy
1838: James Prescott Joule
further investigated the relationship between heat and motion.
He concluded that heat and motion is relative to each other

3. What is Heat!
Heat: is a form of energy caused by the internal motion of molecules of matter.
What are molecules?
Atoms combined in a covalent bond.
Module 1: Basic Concepts - Kinetics #1 (Low Position) | Basic Concepts in Environmental Sciences | APTI | USEPA

4. How and what is heat transfer?
Heat can be transferred 3 ways:
Conduction
Convection
Radiation
Heat transfer is when matter passes heat on to another object.
Important! Heat is transferred from a warmer place to a cooler place.

5. What is Conduction?
Conduction is a process by which heat is transferred through a form of matter by direct contact.
Remember! Fast moving molecules have more heat energy than slow moving molecules.

6. How can you cook or maintain heat instead of losing heat when cooking or heating a house?
You need an insulator!
What is an insulator?
An insulator is a type of material that is used to trap heat and prohibit heat from being transferred.

7. Conductors Insulators
Conductors vs Insulators
Conductors Insulators
Conductors transfer heat
to other substances.
Ex: Iron, aluminum, copper, silver, gold are good conductors
Insulators do not
transfer heat.
Help to keep heat trapped
Ex: glass, wood and plastic

8. Why does metal feel colder than wood, if they are both at the same temperature?
Metal is a conductor, wood is an insulator.
Metal conducts the heat away from your hands.
Wood does not conduct the heat away from your hands, so the wood feels warmer than the metal.

9. What is Convection of Heat?
Convection is the use of molecules moving up and down called convection currents to transfer heat.
What happens to the particles in a liquid or a gas when you heat them?
1st Molecules become hot and rise, spreading out and becoming less dense.
2nd Then they transfer heat and cool becoming more dense and sink. Creating a current up and down.

10. What are convection currents?
Liquid or gas molecules:
1 - Cooler, more d____, fluids or gases sink through w_____, less dense fluids or gases.
ense
armer
2 - In effect, warmer liquids and gases r___ up.
ise
3 - Cooler liquids and gases s___.
ink

11. The third method of heat transfer . . . .
RADIATION
How does heat energy get from the Sun to the Earth?
Radiation is when there are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ?

12. Measuring Temperature
What is temperature?
Temperature is the measurement of the average kinetic energy within molecules.
What is kinetic energy?
Kinetic energy is the amount of energy an object possesses because it is in motion.
What is potential energy?
Potential energy is the amount of energy stored in matter. Ex: gas or fuel when burned there is a release of stored heat energy
There are 3 temperature scales:
Celsius ( Metric System) (ºC)
Kelvin (Metric System) (K)
Fahrenheit

13. WHAT IS SPECIFIC HEAT? Cp is . . . . Q = m x T x Cp
SPECIFIC HEAT: The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin).
Specific Heat is a physical property of matter.
Each sample of matter has its own specific heat number just like each type of matter has its own density value.
Q = m x T x Cp

14. Equation to solve for the amount of heat gained or lost from matter:
HOW TO SOLVE FOR THE AMOUNT OF HEAT GAINED OR LOST FROM MATTER
Equation to solve for the amount of heat gained or lost from matter:
Q = m x T x Cp
Q = is the Amount of energy, gained or lost measured in calories or joules
m = mass of the substance measured in grams
T = change in temperature (T final temperature – T initial temperature)
Cp = specific heat of substance

15. Specific Heat of Water
CONSTANT: The Specific Heat of water is always: J/g x C = 1 calorie Remember: The specific heat of any substance is a constant number!

17. UNITS for HEAT ENERGY Q = (Quantity of heat energy)
Heat energy is measured in either Joules(J), kilojoules (kJ), calories (cal) or kilocalories (kcal).

18. Measuring Temperature
How to convert between Kelvin and Celsius?
Use the following equations:
K = ºC ºC = K - 273
Celsius:
Scale most commonly used in science
Freezing point of water 0 (ºC)
Boiling point of water 100 (ºC)
There are negative quantities
Kelvin:
Has the lowest possible temp:
Absolute Zero degrees below 0
Freezing point or water 273 K
Boiling point of water 373 K

19. Measuring Temperature
How to convert between Fahrenheit and Celsius?
Use the following equations:
F = 9/5 x (C+32ºC) C = 5/9 x (F-32)

20. QUICK WRITE QUESTIONS
The faster molecules of an object move, the more ____________ the object possesses.
______________ is the measurement of how much kinetic energy is present in a substance at a molecular level.
Convert -273 degrees C = ____________ Fahrenheit.
How do convection currents take place? Include the words density, molecules, temperature, drop and rise in your answer.
What type of heat transfer occurred in your lab at station 3 with the gold ring? Explain what, how and why it occurred.
What is heat of fusion and heat of vaporization?

21. Example:If you place a metal spoon in a hot pot.
What happens to the metal spoon?
The heat from the hot pot is transferred to the metal spoon.
This is called?
Conduction

22. How do convection currents transfer heat in liquid molecules?

23. How do convection currents transfer heat in liquid molecules?
Cools at the surface
Convection current
Hot water rises
Cooler water sinks

24. Why is it windy at the seaside?

25. Why is it windy at the seaside?

26. How does convection help keep a refrigerator cold?

27. How does convection help keep a refrigerator cold?
Where is the freezer compartment put in a fridge?
Freezer compartment .

28. How does convection help keep a refrigerator cold?
Where is the freezer compartment put in a fridge?
Freezer compartment
It is warmer at the bottom, so this warmer air rises and a convection current is set up.
It is put at the top, because cool air sinks, so it cools the food on the way down.

29. Convection Q and A Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

30. Quick Write: Determine the specific heat of an unknown metal that required 2,560.0 cal of heat to raise the temperature of g from 15.0 oC to oC?
Steps to Solve for Q
Label each unit in the word problem according to which value it is in the Specific Heat equation.
Identify what you are solving for?
Plug in each value in the equation with correct labels.
Solve.
Label your answer with correct units!
Cp = cal /g -oC

31. Thursday, March 8th Quick Write : ) Homework: Objectives:
Iron metal has a specific heat of J/goC. How much heat is transferred to a 5.00 g piece of iron, initially at 20.0 oC, when it is placed in a beaker of boiling water?
Homework:
.See Mrs. Fugarino during Activity
Period to make corrections to your quiz
Today!
2. Test Friday on Specific
Heat Word Problems, Temperature
Conversions, Forms of Heat transfer
and correct labelling units and decimal points during calculations.
Objectives:
Critically analyze and use the appropriate math skills to Calculate specific heat
Solve specific heat word problems.
Label units appropriately

32. PRACTICE PROBLEM #7 180. J 1.23 x 103 cal 31.1 oC 1.28 J/g oC
1. Iron metal has a specific heat of J/goC. How much heat is transferred to a 5.00 g piece of iron, initially at 20.0 oC, when it is placed in a beaker of boiling water?
2. How many calories of energy are given off to lower the temperature of g of iron from oC to 35.0 oC?
3. If 3.47 kJ were absorbed by 75.0 g H2O at 20.0 oC, what would be the final temperature of the water?
4. A 100. g sample of water at 25.3 oC was placed in a calorimeter g of lead shots (at 100 oC) was added to the calorimeter and the final temperature of the mixture was 34.4 oC. What is the specific heat of lead?
5. A 17.9 g sample of unknown metal was heated to oC. It was then added to g of water in an insulted cup. The water temperature rose from oC to 23.98oC. What is the specific heat of the metal in J/goC?
180. J
1.23 x 103 cal
31.1 oC
1.28 J/g oC
0.792 J/goC

33. Radiation Q and A Radiation travels in straight lines True/False
Radiation can travel through a vacuum
Radiation requires particles to travel
Radiation travels at the speed of light

34. Calculate how to solve for. . .
Specific Heat Cp m
Change in T
From
Q=mCT

35. Radiation Q and A Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped around marathon runners at the end of a race?
The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

36. Heat of Fusion Q = m x Hf(heat of fusion)
Is the amount of energy absorbed to bring a solid to liquid form during melting.
Is the phase change called fusion or melting on a phase change diagram.
During this phase: Potential Energy increases and Kinetic Energy is constant.
The equation to solve for the heat of fusion is:
Q = m x Hf(heat of fusion)
A constant value for water = 334j/g

37. Heat of Vaporization Q = m x Hv(heat of vaporization)
Is the amount of energy absorbed to bring a liquid to gas form during vaporization.
Is the phase change called vaporization on a phase change diagram.
During this phase: Potential Energy increases and Kinetic Energy is constant.
The equation to solve for the heat of fusion is:
Q = m x Hv(heat of vaporization)
A constant value for water = 2,260j/g

38. Emission experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.
shiny metal
radiation
dull black
emitting

39. Absorption experiment
Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.
dull black
radiation
shiny metal
absorbing

40. Absorption versus Emission?
Shiny metal
Dull metal
Dull black
Shiny black

41. Why are Metals good conductors but not insulators?
The outer e______ of metal atoms drift, and are free to move.
lectrons
When a metal is heated, the ‘sea of electrons’ gain k_____ energy and transfer it throughout the metal.
inetic
Insulators, such as w___ and p____, do not have the ‘sea of electrons’.
This is why they do not conduct heat as well as metals.
ood
lastic

42. Knowing its Q value, its mass, and its T, its Cp can be calculated
A calorimeter is used to help measure the specific heat of a substance.
Knowing its Q value, its mass, and its T, its Cp can be calculated
T is measured for water to help get its heat gain
First, mass and temperature of water are measured
Then heated sample is put inside and heat flows into water
This gives the heat lost by the substance

43. 1. Which of the following is not a method of heat transfer?
A. Radiation
B. Insulation
C. Conduction
D. Convection

44. 2. In which of the following are the particles closest together?
A. Solid
B. Liquid
C. Gas
D. Fluid

45. 3. How does heat energy reach the Earth from the Sun?
A. Radiation
B. Conduction
C. Convection
D. Insulation

46. 4. Which is the best surface for reflecting heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black

47. 5. Which is the best surface for absorbing heat radiation?
A. Shiny white
B. Dull white
C. Shiny black
D. Dull black

48. What is SPECIFIC HEAT? Cp is . . . .
SPECIFIC HEAT: The quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin).
Q = m x T x Cp

49. How do convection currents transfer heat in liquid molecules?
Cools at the surface
Convection current
Hot water rises
Cooler water sinks

50. Why is it windy at the seaside?

51. How does convection help keep a refrigerator cold?
Where is the freezer compartment put in a fridge?
Freezer compartment
It is warmer at the bottom, so this warmer air rises and a convection current is set up.
It is put at the top, because cool air sinks, so it cools the food on the way down.

52. Convection Q and A Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.