Lets start with a new symbol

1
Lets start with a new symbol

• Q. Q is for Heat
• Measured in Joules.
• Heat is a form of energy.

2
James Prescott Joule

• Discovered that heat was form of energy.
• Found that when water is stirred, temperature
  increases.

3
James Joule

• Experimented with falling masses turning paddles
  in water.
• Figured out how much mechanical energy is needed
  to change temperature.
• Got a unit named after him.

4
Units of Heat

• Joule is most common heat unit.
• Also, there is the calorie.
• Calorie is the amount of energy necessary to
  raise the temperature of 1 g of water by 1 C .
• Units to measure heat.
• calorie Energy needed to raise
• 1 g of water by 1C.
• 1 cal 4.186 Joules.

5
Calories and calories.

• Calories and calories are not the same thing.
• If C is uppercase, it is a dietary calorie (on
  your food label.)
• One Calorie 1000 calories
• One Calorie 1 kilocalorie
• One Calorie 4186 Joules

6
Units of Heat, cont.

• Also BTU
• BTU stands for British Thermal Unit
• A BTU is the amount of energy necessary to raise
  the temperature of 1 lb of water 1 F

7
New Symbol

• Specific heat c
• Amount of heat needed to raise
• 1 kg of a material 1 C.
• Units J / kg C
• Depends on the substance. Look it up.
• Specific heat questions are on the JCCC final.

8
Specific Heat equation

• Q mc?T
• Heat massspecific heatTemp. Change
• If ?T is positive, material gains heat.
• If ?T is negative, material gives up heat.

9
Problem

• The Specific Heat of water is 4186 J/kgC.
• How much heat is needed to raise 6.2 kg of water
  from 10 to 85 Celsius?
• Do in PP notes.
• Specific heat questions like this are on the JCCC
  final.

10
Problem

• The Specific Heat of water is 4186 J/KgC.
• How much heat is needed to raise 6.2 kg of water
  from 10 to 85 Celsius?
• Q mc?T
• Q 6.2kg4186 J/KgC75C

11
Calorimetry

• Measurement of heat flow from a hot material to a
  cold material (usually Water).
• Heat flow into water is calculated based upon the
  temp. change of the water.
• Conservation of energy applies to the isolated
  system. Dont let any heat escape so that all
  goes into the water. (Insulated system)
• The energy that leaves the warmer substance
  equals the energy that enters the water.
• ?Qhot - ?Qcold
• Know Q mc?T for final.

12
Easy problem

• Know for JCCC Final
• ?Qhot - ?Qcold
• mc?Thot mc?Tcold

13
Easy problem

• 1 kg of water at 70 C is mixed with 1 kg of water
  at 60 C. What is the final temp?

14
Easy problem

• 1 kg of water at 70 C is mixed with 1 kg of water
  at 60 C. What is the final temp?
• mc?Thot mc?Tcold
• 1 kg x 4186 J/kgK x (70C Tf)
• 1 kg 4186 J/kgK x (Tf 60C)

15
Easy problem

• 1 kg of water at 70 C is mixed with 1 kg of water
  at 60 C. What is the final temp?
• 2 kg of water at 70 C is mixed with 1 kg of water
  at 60 C. What is the final temp?

16
Problem

• For breakfast you consume 320 dietary Calories.
• You decide to work this off by lifting a 25 kg
  barbell .4 m.
• How many times will you have to repeat this
  motion to burn off breakfast?

17
Problem

• For breakfast you consume 320 dietary Calories.
• Instead, you (60 kg) decide to spring from rest
  to 5 m/s.
• How many repetitions of this will you need to do?

18
Still talking about breakfast

• If instead of eating that food, you set it on
  fire, how much water could it bring from 0C to
  100 C?
• Q mc?T
• m Q /c?T

19
What else does heat do?

• If heat is added to a substance, what else could
  happen besides ?T?

20
Phase Change

• Temperature remains constant during phase change.
  
• E.g. Ice will continue to absorb heat at 0 C
  without changing temp. The temp will not be 1 C
  until all of the ice has melted.
• See graph next slide.

21
Graph of Ice to Steam
22
Phase Change

• 3 Basic types of Phase Change
• Melting/Freezing Liquid/Solid
• Boiling/Condensing Gas/Liquid
• Sublimation/Deposition Gas/Solid

23
New Symbol

• l l is for latent heat.
• Amount of heat absorbed, per kilogram, for a
  change from one phase to another.
• Heat absorbed during a phase change does not
  change temperature, so it is latent.
• Units J/kg

24
Latent Heat, cont.

• Depends on both substance and phase change. Just
  something to look up.
• Latent heat of fusion, Lf, is used for melting or
  freezing
• Latent heat of vaporization, Lv, is used for
  boiling or condensing
• Latent heat of sublimation, Ls, is used for
  sublimation or deposition.

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Equation

• Q m l

26
Problem

• A gram of H20 is at -30 C. How much heat total
  is needed to raise it to H20 at 120 C?

27
Multistep processes.

• A lot of problems will involve both a temperature
  change and a phase change. Evaluate the Q for
  each step separately, and then add them together.
  

28
Problem

• How many steps?

29
Graph of Ice to Steam
How many steps? 5 1- Ice to 0 C 2- Melting 3-
Water to 100 C 4- Boiling 5- Steam to 120
C Qtotal Q1 Q2 Q3 Q4 Q5
30

• End here in 2012

31
Problem

• How many steps?
• 5
• 1- Ice to 0 C
• 2- Melting
• 3- Water to 100 C
• 4- Boiling
• 5- Steam to 120 C
• Qtotal Q1 Q2 Q3 Q4 Q5

32
Useful Information

• For H20
• cice 2090 J/kgº C
• lf 3.33 X 105 J/kg
• cwater 4186 J/kgº C
• lv 2.26 x 106 J/kg
• csteam 2010 J/kgº C

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Warm the Ice

• Qtotal Q1 Q2 Q3 Q4 Q5
• Q1 -gt Ice from -30 to 0
• Temp. change, so use specific heat.
• Q1 micecice?Tice
• .001kg 2090 J/kgº C (0 - -30)

34
Melt the Ice

• Qtotal 63 J Q2 Q3 Q4 Q5
• Q2 -gt Ice from 0 to water _at_ 0
• Phase change, so use latent heat.
• Q2 micelfice
• .001kg 3.33 X 105 J/kg

35
Warm the Water

• Qtotal 63 J 333 J Q3 Q4 Q5
• Q3 -gt Water from 0 to 100
• Temp. change, so use specific heat.
• Q3 mwatercwater?Twater
• .001kg 4186 J/kgº C (100 - 0)

36
Boil the water

• Qtotal 63 J 333 J 419 J Q4 Q5
• Q4 -gt Ice from 0 to water _at_ 0
• Phase change, so use latent heat.
• Q4 mwaterlfwater
• .001kg 2.26 x 106 J/kg

37
Warm the Steam

• Qtotal 63 J 333 J 419 J 2260 J Q5
• Q5 -gt Steam from 100 to 120
• Temp. change, so use specific heat.
• Q5 msteamcsteam?Tsteam
• .001kg 2010 J/kgº C (120 - 100)

38
Warm the Steam

• Qtotal 63 J
• 333 J
• 419 J
• 2260 J
• 40 J
• Qtotal 3115 J

39
Graph of Ice to Steam
40
Problem

• The latent heat of lead is 24500 J/kg, and the
  melting point is 327.5 C. How much heat is
  needed to bring 17 kg of solid lead at 327.5 C to
  17 kg of liquid lead at 327.5 C?

41
Problem

• Back in October, we learned that the most
  powerful person in the class was about 1050
  Watts.
• If we gave him an electrical generator bike, how
  long would it take him to boil a kg of water from
  room temp?

42
Problem

• 400 g of Copper (c 386 J/kgC) at 95 C is placed
  into a kilogram of water at 5 C. What will the
  final temperature of the mixture be?

43
Another problem.

• 10 kilograms of Aluminum (c 900 J/kgC) are at
  130 C. A 50 g Ice cube at -5 C is dropped onto
  the aluminum and melts, then boils away. What is
  the final temperature of the Al?

44
More than 2 things

• S?Q 0
• Or
• ?Q1 ?Q2 ?Q3 0

45
Problem

• 400 ml of water at 40 C is poured into a .3 kg
  glass beaker (cglass 837 J/C) and a .5 kg block
  of Al at 37 C (cAl 900 J/C) is dropped in.
• What will the equilibrium temp be?