heat and thermodynamics. warm-up below is a graph of temperature (y) versus time as energy is added....
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Heat and Thermodynamics
Warm-upBelow is a graph of temperature (y) versus
time as energy is added. Which letters correspond to a phase change of that material?
a)A and Cb)B and Dc)A and Bd)C and D
COMPARE TEMPERATURE AND HEAT
A
B CD
T (K)
t in seconds
How to we measure energy?Energy is measured in JoulesHowever heat and energy have several other
units as wellBTU’sCalories /kcalscalories
We measure our food in terms of Calories because this is the amount of energy it takes to break it down.
Level 1Complete the level 1 worksheet for Heat (15
minutes to do so) The faster you work the less homework you will have.
http://www.stricklandphysics.net/uploads/8/3/5/2/8352741/heat_math_introduction.pdf
Equations
Specific Heat (Review)Specific heat is defined as the amount of
energy (in Joules) that it takes to raise the temperature of 1 gram substance by 1 degree C, or by 1 K.
Substancec in J/gm K
c in cal/gm K orBtu/lb F
Molar CJ/mol K
Aluminum0.900
0.215
24.3
Bismuth0.123
0.0294
25.7
Copper0.386
0.0923
24.5
Brass0.380
0.092
...
Gold0.126
0.0301
25.6
Lead0.128
0.0305
26.4
Silver0.233
0.0558
24.9
Tungsten0.134
0.0321
24.8
Zinc0.387
0.0925
25.2
Mercury0.140
0.033
28.3
Alcohol(ethyl) 2.40.58
111
Water4.186
1.00
75.2
Phase ChangeLatent Heat (L) measured in J/kg indicates
the amount of energy required to cause a substance to change phasesTwo types Fusion and Vaporization
L is typically large compared to Cp
Calorimetry
The heat lost by the hotter object will be gained by the cooler one
Each Q represents heat
Tf for each one is the final temperature of both. Ti is unique for each compound and is given in the problem
This is how they find how many calories are in your food!
Calorimetry Example (LEVEL 2)A piece of copper has a mass of 20 kg and is
warmed to 140 degrees C. It is placed in 200 kg of water that is at 2 degrees C. What is the final temperature of both materials?
Phase Change Energy (Level 2)If nitrogen starts out as a gas at 300 K. How
much energy is required to liquefy 2 kg of nitrogen if nitrogen has a specific heat of 1,040 J/Kg K and a Latent heat of vaporization of 200,000 J/kg. Nitrogen boils at 77 K.
Group Work PracticePractice your skills at Level 2 Questionshttp://www.stricklandphysics.net/uploads/8/3/
5/2/8352741/group_work_l2_heat.pdf