spark 09/22/2011
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Spark 09/22/2011On a very warm day at the beach,
which heats up faster, the water or the sand?
Once night rolls in, which cools faster?If some materials heat up faster than
others, although exposed to the same energy, then where does the energy go if something is not getting hotter? Why might some materials heat up faster
than others?
Reading QuestionsRead the Matter document up to
“Temperatures in Kelvin”What is the KMT?What is the difference between heat and
temperature?Why is the Kelvin temperature scale
used?How does the K scale convert to Celcius?
http://mutuslab.cs.uwindsor.ca/schurko/animations/waterphases/status_water.htm
Enthalpy and Heat
The study of energy and its transformations is known as thermodynamics. Energy is commonly defined as the capacity to do work or to transfer heat. Work is energy used to cause an object with mass to move. Heat is energy used to cause the temperature of an object to increase.
Enthalpy and Heat
Kinetic energy is the energy of motion, represented by the equation:
Ek = 1/2 mv2
Atoms and molecules have mass and are in motion, therefore they have kinetic energy.
Enthalpy and Heat
The SI unit for energy is the joule: J = 1 kg-m2/s2
A 2 kg mass moving at 1 m/s possesses a kinetic energy of 1 J:
Ek = 1/2 mv2 = 1/2 (2 kg) (1 m/s)2
= 1 kg-m2/s2 = 1 J Since a joule is a small amount of energy,
the unit kilojoules, kJ, is often used when describing chemical reactions.
Enthalpy and Heat
Traditionally, energy changes in chemical reactions have been expressed in calories, a non-SI unit.
A calorie was originally defined as the amount of heat energy required to raise the temperature of 1 g of water from 14.5 oC to 15.5 oC. It is now defined in terms of the joule:
1 cal = 4.184 J (exactly)
Enthalpy and Heat
A related energy unit used in nutrition is the nutritional Calorie (note the capital letter).
1 Cal = 1000 cal = 1 kcal
E N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - H
heat content in matter:
E N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - HE N T H A L P Y - H
heat content in matter:
natural systems tend to go from a state of high energy to a state of low energy.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
The phases of matterrepresent "classes" of molecular motion found at different temperatures.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
The phases of matterrepresent "classes" of molecular motion found at different temperatures.
XKinetic Energ
y
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
The phases of matterrepresent "classes" of molecular motion found at different temperatures.
XHEAT
0
0.5
1
1.5
2
2.5
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3.5
4
4.5
5
E Thermal E Internal E Chem
Hot Coffee
Thermal E = 4
Internal E = 2
Solids = 1
Liquids = 2
Gases = 3
Chemical = 0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
E Thermal E Internal E Chem
0
0.5
1
1.5
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2.5
3
E Thermal E Internal E Chemical
Coffee Before Coffee After
Total Energy = 7 units
Total Energy = 5 units
Missing 2 units of E: Where did they go?
How can we diagram energy flow when a cup of coffee cools?
Energy Flow Diagram Is energy flowing in or
out of the system? 2 units of energy
leave causing the coffee to cool.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
E Thermal E Internal E Chem
0
0.5
1
1.5
2
2.5
3
E Thermal E Internal E Chemical
Cup of Hot Coffee
E
E
7 units - 2 units = 5 units
Spark
Does hot water or cold water freeze faster?Explain using the KMT.
Are you aware of the Mpemba Effect?What are the four conditions that make the Mpemba Effect possible?(p2-3)
Do you have an explanation for the Mpemba Effect?
HMMMM…
Can water boil if it’s cold?Explain using the KMT.
http://youtu.be/8oCjj8iDB9I
http://youtu.be/QGSo7zcg_qA
http://youtu.be/OHY9fFQhX68
http://youtu.be/RPlCO3AITV4
http://youtu.be/9q5gEZGoBnk
Heat Matter does not contain heat, it contains energy
(kinetic, thermal, internal energy, chemical energy).
Heat is energy that is transferred from hot to cold Heat is measured in calories or Joules 1 calorie = 4.185 J Measure average kinetic energy with a thermometer
and call it temperature How can we measure heat if things don’t heat and cool
the same way?
Specific Heat Capacity Think of it as heating ability… The amount of heat energy that is required
to raise the temperature of one gram of a substance by one degree Celsius is called the specific heat capacity, or simply the specific heat, of that substance.
Water, for instance, has a specific heat of 1.0 calorie per gram degree Celsius [1.0 cal / (g x o C)].
Water becomes our standard for studying energy.
Specific Heat Capacity Water
So:It takes 1 calorie of heat to raise 1 gram of
water 1 degree
How many calories are released if 1 gram of water cools 1 degree?
How many calories are needed to heat 1 gram of water at OoC to boiling (100oC)?
1 calorie
100 cal
BTU Inquiry Lab Tips
Rate of BTU production be lab burner.
1 BTU = Nrg to increase 1 lb of water @39.1oF, 1oF
Convert measurable metric masses and temperatures into BTU’s and predict the time to get a hypothetical rate (BTU/sec)
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
q = U + P Vq = heat gained or lostU = internal energyP = PressureV = volumeSee Energy notes
Spark 09/27/2011
How much energy is needed to melt a 10 lb bag of party ice at 0o C? (heat of fusion = 334 J/g or 80 cal/g) There are 2.2 lbs/1 kgHfus - heat of fusion
The amount of heat needed to change one
gram of a solid into a liquid at its melting point.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
Hfus - heat of fusion
As energy is added to a solid at its melting point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
Hfus - heat of fusion
The amount of heat needed to change one gram of a solid into a liquid at its melting point.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
Hfus H2O = 334 J/g
Hfus lead = 24.72 J/g
When increasing temperature,the concentration of gas-phasemolecules just above thesurface of the liquid increases.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
As energy is added to a liquid at its boiling point, ALL the energy is used to increase the kinetic energy of the molecules during the phase change.
E N T H A L P YE N T H A L P YE N T H A L P YE N T H A L P Y
Hvap - heat of vaporization
The amount of heat needed to change one gram of a liquid into a gas at its boiling point.
Spark q = m x ΔT x s
50.0 grams of hot water (65.0oC) are added to a calorimeter that has 25.0 grams of water at 5.0oC. After mixing the final temperature reached was 44.0oC.1 cal = 4.185 J = E to raise 1 g H2O 1oC
How much energy was released from the hot water?How much was absorbed by the cold water?Is energy being conserved? Does the nrg released = the nrg absobed?
Spark
With your group, calculate your mean calorimeter constant.
Send a representative to me with your value for spreadsheet credit.
Be sure that all group members know what the calorimeter constant reflects!
Specific Heat Specific Heat CapacityCapacity
Specific Heat Specific Heat CapacityCapacity
The heat required to raise
the temperature of onegram of a substance byone Celsius degree.
change temp within change temp within phasephase
q = m Cp
q = heat gained or lostm = mass= “change in temperature”Cp = specific heat capacity
Specific Heat CapacityThe amount of heat energy involved in
changing the temperature of a sample of a particular substance depends on three parameters -- the specific heat of the substance, the mass of the sample, and the magnitude of the temperature change.
The Greek letter delta (Δ) is used to indicate a change. Δ T = temperature final - temperature
initial
The General Idea Behind Specific Heat Labs
Both ice or a heated sample will be placed into a crude calorimeter, consisting of water contained in a plastic foam cup. Shortly after mixing, the sample will have come to the same temperature as the water or the water temperature will increase or decrease depending on the change. Because Styrofoam is a good insulator, heat cannot easily escape from the calorimeter to the surroundings.
Specific Heat LabsThe heat lost or gained by the sample should
be equal to the heat gained or lost by the water.
The amount of heat energy gained by the water will be calculated in the following manner:
heat gained water = specific heat water X mass water X ΔTwater
The heat lost by the sample is given by a similar equation:
heat lostsample = specific heat sample X mass sample X ΔTsample
Because the heat gained must equal the heat lost, a third equation can be written:
specific heat water X mass water X ΔT water = specific heat sample X mass sample X ΔT sample
The specific heat of water is known. The temperature changes of the
water, and of the sample, can be measured, as can the mass of the water and the mass of the sample.
Using this data, the specific heat of the sample can be calculated.
Calorimetry values are all determined based on the temperature changes of the water sample.
Specific Heat Specific Heat CapacityCapacity
Specific Heat Specific Heat CapacityCapacity
Cp of ice = 2.06 J/g.Co
Cp of water = 4.18 J/g.Co
Cp of steam = 2.02 J/g.Co
Cp of copper = .385 J/g.Co
q=mHvap change phase
q=mHFUS- change phase
q=mCp - change temp
q=mCp - change temp
q=mCp - change temp
How much heat is needed toconvert 250 grams of ice at -30 oC to vapor at 150 oC?
1. Change temp of ice2. Melt ice3. Change temp of liquid water4. Vaporize water5. Change temp of vapor6. Add total heat used
Spark
Get your materials for the specific heat lab.
3 groups may use burners otherwise use a hot plate.
Use 2 foam cups instead of oneCalorimeter water should be cold.I will give you your metals once you have everything else.
P h a s e D i a g r a mP h a s e D i a g r a m
A g r a p h s h o w i n g A g r a p h s h o w i n g t h e p h a s e s o f t h e p h a s e s o f m a t t e r a s t h e m a t t e r a s t h e y r e l a t e t o y r e l a t e t o t e m p e r a t e m p e r a t u r e a n d t u r e a n d p r e s s u r e . p r e s s u r e .
M a j o r p o i n t s o n a p h a s e d i a g r a m
M a j o r p o i n t s o n a p h a s e d i a g r a m
Normal Atmospheric PressureNormal Atmospheric Pressure
Triple pointTriple point
Boiling PointBoiling Point
Melting pointMelting point
Critical temperatureCritical temperature
V a n d e r W a l l s A t t r a c t i o n
V a n d e r W a l l s A t t r a c t i o n
T h e f o r c e o f T h e f o r c e o f a t t r a c t i a t t r a c t i o n o n b e t w e e n b e t w e e n
m o l e c u l e sm o l e c u l e s
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