Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer...
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Transcript of Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer...
![Page 1: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/1.jpg)
Intro to Thermodynamics
Mr Nelson – 2010
![Page 2: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/2.jpg)
Energy
• Energy is the ability to do work or transfer heat.– Energy used to cause an object to move is called work.
– Energy used to cause the temperature of an object to rise is called heat.
![Page 3: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/3.jpg)
Potential Energy
Potential energy is energy an object possesses by virtue of its position or chemical composition.
![Page 4: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/4.jpg)
Kinetic Energy
Kinetic energy is energy an object possesses by virtue of its motion.
12
KE = mv2
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Units of Energy
• The SI unit of energy is the joule (J).
• An older, non-SI unit is still in widespread use: the calorie (cal).
1 cal = 4.184 J
1 J = 1 kg m2
s2
![Page 6: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/6.jpg)
Energy in Foods
Most of the fuel in the food we eat comes from carbohydrates and fats.
![Page 7: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/7.jpg)
System and Surroundings
• The system includes the molecules we want to study (here, the hydrogen and oxygen molecules).
• The surroundings are everything else (here, the cylinder, piston and the universe).
![Page 8: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/8.jpg)
Work
• Energy used to move an object over some distance is work.
• w = F d
where w is work, F is the force, and d is the distance over which the force is exerted.
![Page 9: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/9.jpg)
Heat
• Energy can also be transferred as heat.
• Heat flows from warmer objects to cooler objects.
![Page 10: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/10.jpg)
Conversion of Energy
• Energy can be converted from one type to another.
• For example, the cyclist above has potential energy as she sits on top of the hill.
![Page 11: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/11.jpg)
Conversion of Energy
• As she coasts down the hill, her potential energy is converted to kinetic energy.
• At the bottom, all the potential energy she had at the top of the hill is now kinetic energy.
![Page 12: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/12.jpg)
First Law of Thermodynamics
• Energy is neither created nor destroyed.• The total energy of the universe is a constant; if the system
loses energy, it must be gained by the surroundings, and vice versa.
![Page 13: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/13.jpg)
Exchange of Heat between System and Surroundings
• When heat is absorbed by the system from the surroundings, the process is endothermic.
![Page 14: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/14.jpg)
Exchange of Heat between System and Surroundings
• When heat is released by the system into the surroundings, the process is exothermic.
![Page 15: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/15.jpg)
Heat Capacity and Specific Heat
The amount of energy required to raise the temperature of a substance by 1C is its heat capacity.
![Page 16: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/16.jpg)
Heat Capacity and Specific HeatWe define specific heat as the amount of energy required to raise the temperature of 1 g of a substance by 1 C .
![Page 17: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/17.jpg)
Heat Capacity and Specific Heat
Specific heat, then, is
Or the way we usually use the equation:q = m c T
Specific heat =heat transferred
mass temperature change
c =q
m T
![Page 18: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/18.jpg)
Constant Pressure CalorimetryBy carrying out a reaction in aqueous solution in a simple calorimeter such as this one, one can indirectly measure the heat change for the system by measuring the heat change for the water in the calorimeter.
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Constant Pressure Calorimetry
Because the specific heat for water is well known (4.184 J/g-K), we can measure H for the reaction with this equation:
q = m c T
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Enthalpy
• Enthalpy is the heat content of a system at constant pressure and volume:
Enthalpy = H
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Enthalpy
• The absolute amount of Enthalpy cannot be measured, so it is indirectly measured with temperature.
• When the system changes at constant pressure, the change in enthalpy, H, is
H = Hfinal - Hinital
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Enthalpy
• So, at constant pressure, the change in enthalpy is the heat gained or lost.
H = q
![Page 23: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/23.jpg)
Bomb Calorimetry
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Different H’s
• Every delta H has the same type of definition:– The heat released or absorbed when:
Hfusion
Hsolid
Hformation
Hreaction
Hvaporization
Hcombustion
![Page 25: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/25.jpg)
Endo vs Exo
• A process is endothermic when H is positive.
![Page 26: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/26.jpg)
Endo vs Exo
• A process is endothermic when H is positive.
• A process is exothermic when H is negative.
![Page 27: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/27.jpg)
Heat Transfer Problem 1
Calculate the heat that would be required an aluminum cooking pan whose mass is 400 grams, from 20oC to 200oC. The specific heat of aluminum is 0.902 J g-1 oC-1.
Solution
Q = mCT
= (400 g) (0.902 J g0.902 J g-1-1 ooCC-1-1)(200)(200ooC – 20C – 20ooCC))
= 64,944 J= 64,944 J
![Page 28: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/28.jpg)
Heat Transfer Problem 2 What is the final temperature when 50 grams of water at
20oC is added to 80 grams water at 60oC? Assume that the loss of heat to the surroundings is negligible. The specific heat of water is 4.184 J g-1 oC-1
Solution: Q (Cold) = Q (hot) mCT= mCT Let T = final temperature
(50 g) (4.184 J g-1 oC-1)(T- 20oC) = (80 g) (4.184 J g-1 oC-1)(60oC- T)
(50 g)(T- 20oC) = (80 g)(60oC- T) 50T -1000 = 4800 – 80T 130T =5800 T = 44.6 oC
![Page 29: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/29.jpg)
Chemical Reactions
In a chemical reaction
• Chemical bonds are broken
• Atoms are rearranged
• New chemical bonds are formed
• These processes always involve energy changes
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Energy Changes
• Breaking chemical bonds requires energy
• Forming new chemical bonds releases energy
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Exothermic and Endothermic Processes
• Exothermic processes release energy
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4H2O (g)
+ 2043 kJ
• Endothermic processes absorb energy
C(s) + H2O (g) +113 kJ CO(g) + H2 (g)
![Page 32: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/32.jpg)
Energy Changes in Chemical Reactions
In an endothermic reaction there is more energy required to break bonds than is released when bonds are formed.
The opposite is true in an exothermic reaction.
![Page 33: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/33.jpg)
Enthalpy of Reaction
The change in enthalpy, H, is the enthalpy of the products minus the enthalpy of the reactants:
H = Hproducts − Hreactants
![Page 34: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/34.jpg)
Enthalpy of Reaction
This quantity, H, is called the enthalpy of reaction, or the heat of reaction.
![Page 35: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/35.jpg)
The Truth about Enthalpy
1. Enthalpy is an extensive property.
2. H for a reaction in the forward direction is equal in size, but opposite in sign, to H for the reverse reaction.
3. H for a reaction depends on the state of the products and the state of the reactants.
![Page 36: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/36.jpg)
Hess’s Law
• Hess’s law states that “[i]f a reaction is carried out in a series of steps, H for the overall reaction will be equal to the sum of the enthalpy changes for the individual steps.”
• We can estimate H using published H values and the properties of enthalpy.
![Page 37: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/37.jpg)
Hess’s Law
![Page 38: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/38.jpg)
Hess’s LawThe total enthalpy change depends only on the initial state of the reactants and the final state of the products.
![Page 39: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/39.jpg)
Standard Enthalpies of FormationStandard enthalpies of formation, Hf°, are measured under standard conditions (25 °C and 1.00 atm pressure).
![Page 40: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/40.jpg)
Calculation of H
• Imagine this as occurring in three steps:
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
C3H8 (g) 3 C (graphite) + 4 H2 (g)
3 C (graphite) + 3 O2 (g) 3 CO2 (g)
4 H2 (g) + 2 O2 (g) 4 H2O (l)
![Page 41: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/41.jpg)
Calculation of H
• Imagine this as occurring in three steps:
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
C3H8 (g) 3 C (graphite) + 4 H2 (g)
3 C (graphite) + 3 O2 (g) 3 CO2 (g)
4 H2 (g) + 2 O2 (g) 4 H2O (l)
![Page 42: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/42.jpg)
Calculation of H
• Imagine this as occurring in three steps:
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
C3H8 (g) 3 C (graphite) + 4 H2 (g)
3 C (graphite) + 3 O2 (g) 3 CO2 (g)
4 H2 (g) + 2 O2 (g) 4 H2O (l)
![Page 43: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/43.jpg)
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
C3H8 (g) 3 C (graphite) + 4 H2 (g)
3 C (graphite) + 3 O2 (g) 3 CO2 (g)
4 H2 (g) + 2 O2 (g) 4 H2O (l)
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
Calculation of H
• The sum of these equations is:
![Page 44: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/44.jpg)
Calculation of H
We can also use Hess’s law in this way:
H = nHf°products – mHf° reactants
where n and m are the stoichiometric coefficients.
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H = [3(-393.5 kJ) + 4(-285.8 kJ)] – [1(-103.85 kJ) + 5(0 kJ)]= [(-1180.5 kJ) + (-1143.2 kJ)] – [(-103.85 kJ) + (0 kJ)]= (-2323.7 kJ) – (-103.85 kJ) = -2219.9 kJ
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)
Calculation of H
![Page 46: Intro to Thermodynamics Mr Nelson – 2010. Energy Energy is the ability to do work or transfer heat. –Energy used to cause an object to move is called.](https://reader033.fdocuments.in/reader033/viewer/2022051819/55157cf7550346486b8b52e9/html5/thumbnails/46.jpg)
Energy in Fuels
The vast majority of the energy consumed in the U.S. comes from fossil fuels.