1. Zumdahl • Zumdahl • DeCoste
World of
CHEMISTRY

2. Chapter 10
Energy

3. Objective: To understand the general properties of energy
10.1 The Nature of Energy
Objective: To understand the general properties of energy
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4. 10.1 The Nature of Energy Energy Potential Energy Kinetic Energy
The ability to do work or produce heat
Potential Energy
Energy due to position or composition
Movement of water from high to low to do work
Attractive and repulsive forces used to drive a chemical reaction
Example – combustion of gasoline
Kinetic Energy
Energy do to the motion of the object
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5. Law of Conservation of Energy
Energy can be converted from one form to another but can neither be created or destroyed.
Energy on the universe is constant
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6. Work Work Force acting over a distance
Example: a ball rolling down hill.
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7. What happens if we change the surface of our hill?
Does ball A lose more energy?
What changes?
The amount of heat released
The amount of force (work) applied
Regardless of the amount of heat or work the energy change is constant.
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8. The change in Energy is independent of it pathway.
Work and Heat are dependent of its pathway.
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9. Example of State Function
A State Function is a property of the system that changes independently of its pathways (heat and work are not state functions, they are dependent upon the pathway in which the reaction proceeds).
Example of State Function
Displacement; Energy change
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10. Objective: To understand the concept of Temperature and Heat
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11. What does temperature of a substance tell us about that substance?
Temperature is
a measure of the random motion of the components of a substance.
Example: Ice →liquid H2O →gaseous H2O
Heat can be defined as .
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12. Figure 10.2: Equal masses of hot and cold water.
Suppose we place 1.00 Kg
hot water next to 1.00 Kg of
cold water in an insulated
box. What do you expect to
happen?
Assuming no energy is
lost to the air how can we
determine the final temp.
of the two samples?
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13. Figure 10.3: H2O molecules in hot and cold water.
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14. Remembering that heat is the measure of energy flow do to temperature difference:
Tfinal = Thot initial + Tcold initial = 90° C + 10°C = 50
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15. Figure 10.4: H2O molecules in same temperature water.
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16. Thermal Energy of an object
Review
Temperature
the measure of the random motions of the components
Heat
the flow of energy due to temperature differences
Thermal Energy of an object
The random motions of the components of the object
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17. 10.3 Exothermic and Endothermic
Objective: To consider the direction of energy flow as heat
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18. What are the energy changed that accompany chemical reactions?
When a process results in the evolution of heat, it is said to be
Exothermic: energy flows OUT of a system
When a process results absorbs energy from its surrounding it is said to be
Endothermic
When heat flows into a system it is said to be endothermic
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19. Key Terms System Surroundings
The portion of the universe that we single out to study
Surroundings
The surroundings include everything else in the universe.
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20. Endothermic Reactions
Example: Boiling water to form steam
Where does the energy (absorbed as heat) come from in an endothermic reaction?
The energy is the difference between the potential energy between the reactants and the products
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21. In an Endothermic Reactions:
If energy can neither be created or destroyed, where does the change in energy come from?
In an Endothermic Reactions:
The energy gained by a system must equal the energy lost by the surroundings.
In an Exothermic Reaction:
the energy lost by a system must equal the energy gained by the surroundings
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22. Examples: Endothermic or Exothermic?
Your hands get cold when you touch ice?
Exothermic
Ice melts when you touch it.
Endothermic
Ice cream melts
Propane is burning in a propane torch
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23. 5. Water drops on your skin evaporates Endothermic
6. Two chemicals mixed in a beaker give off heat.
Exothermic
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24. Figure 10.5: The energy changes accompanying the burning of a match.
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25. Explain why energy is a state function, but heat and work are not.
Focus Questions
Explain why energy is a state function, but heat and work are not.
What is probably the most important characteristic of energy?
What is the difference between temperature and heat?
Heat is the flow of energy due to temp. difference.
Temperature is the measurement of random motion
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26. Objective: To understand how energy flow affects internal energy
10.4 Thermodynamics
Objective: To understand how energy flow affects internal energy
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27. First Law of Thermodynamics
The energy of the universe is constant
The internal energy, E, of a system can be defined as the sum of the kinetic and potential energies of all particles in the system.
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28. ∆ E = q + w
∆ (delta) means a change in the function that follows q represents heat w represents work E represent the internal energy
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29. Thermodynamic Quantities Consist of 2 Parts
A number
giving the magnitude of the change
Sign
indicating the direction of the flow of energy
The sign represents the systems point of view
+ indicated energy flows into a system
- indicates energy flows out of a system
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30. Common Units of Energy Calorie (metric unit) Joule (an SI unit)
The amount of energy (heat) required to raise the temperature of one gram of water by one Celsius degree
Joule (an SI unit)
1 calorie = joules
1 cal = J
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31. How much energy (heat) in joules is
If 1 cal/4.184 J is required to change 1.0g of water by 1° C we can assume that it will take twice as much energy to change 2 g of water by 1 ° C
How much energy (heat) in joules is
required to raise the temperature of 7.40
gram of water from 29 ° C to 46 ° C ?
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32. 10.5 Measuring Energy Changes
Objective: To understand how heat is measured
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33. Conversion between calories and joules
Express 60.1 cal of energy in units of joules
60.1 cal X J = 251 J
1cal
How many calories of energy correspond to 28.4 J?
28.4J X 1 cal = 6.67 cal
4.184 J
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34. Specific Heat Capacity
The amount of energy required to change the temperature of one gram of a substance by one Celsius degree.
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35. 1. The amount of substance being heated (number of grams).
The Energy (heat) Required to change the temperature of a substance depends on:
1. The amount of substance being heated (number of grams).
2. The temperature change (number of degrees)
*Note: different substance behave differently to
being heated. Some substances require large
amounts of energy to change temperature , whereas
others require less.

36. Calculations Involving Specific Heat Capacity pg. 298
What quantity in joules is required to heat a piece of iron weighing 1.3 g from 25°C to 46°C?
What is the answer in calories?
A 5.63 sample of solid gold is heated from 21°C to 32°C. How much energy in joules is required?
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37. S = specific heat of capacity M = mass in grams
Q = s X m X ∆ T
Q = Energy required
S = specific heat of capacity
M = mass in grams
∆ T = change in temperature
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38. Quiz 10.1 – 10.3
The portion of the universe that we single out to study is known as:__________
A measure of the random motion of the components of a substance is known as_____
Explain why energy is a state function, but heat and work are not.
The flow of energy due to temperature differences is known as___________.
__________is the ability to do work or produce heat
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39. 10.6 Thermochemistry (Enthalpy)
Objective: To consider the heat (enthalpy) of chemical reactions
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40. Enthalpy
At constant pressure, the change in enthalpy (∆ H) is equal to the energy that flows as heat.
∆ Hp= heat
Where “p” indicates that the process occurred under conditions of constant pressure.
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41. Practice problem pg 302
When 1 mol of methane is burned at constant pressure, 890 kJ of energy is released as heat. Calculate the ∆ H for a process in which 5.8 grams sample of methane is burned at constant pressure.
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42. Calorimeter
A calorimeter is a device used to determine the heat associated with a chemical reaction.
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43. Figure 10.6: A coffee-cup calorimeter.
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44. Objective: To understand Hess’s Law
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45. Enthalpy is a state function
The change in enthalpy for a given process is independent of the pathway for the process
In going from a particular set of reactants to products the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.
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46. Characteristics of Enthalpy Changes
1. If a reaction is reversed, the sign of ∆ H is also reversed. 2. The magnitude of ∆ H is proportional to the quantities of reactants and products in the reaction. If the coefficients in a balanced reaction are multiplied by an integer, then the value of ∆ H must also be multiplied by the same inetger.
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47. 1. If enthalpy is the heat for a reaction, it must have a sign as well as a magnitude. What sign for an exothermic reaction have? Why? 2. Suppose you ran a chemical reaction in a calorimeter. If the temperature of the solution goes from 27 °C to 36°C for a 5.0g sample, how would you determine the energy produced by the reaction? 3.What is Hess’s Law and why is it useful?
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48. 4. The enthalpy of a combustion of solid carbon to form carbon dioxide is kJ/mol °C, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is kJ/mol °C. Using this data, calculate the change in enthalpy for the reaction: 2C(s) + O2 (g) → 2 CO (g)
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49. 10.8 Quality Versus Quantity of Energy
Objective: To see how the quantity changes as it is used
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50. If energy is conserved, why are we concerned about having enough energy to use?
Suppose we drive from Evansville to Indianapolis – we put gas in our car to do work.
The energy in the bonds react with oxygen (combust – bond are broken) and energy is released to do work.
During this process we release energy in the form of heat (i.e. the quantity of heat is transferred , thus conserved).
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51. What happens to the quality of the energy?
C8H18(l) + O2(g) → CO2 (g) + H2O (g) + energy
Which energy is easier to use?
When we utilize energy to do work we degrade its usefulness (quality).
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52. “heat death” of the Universe
Eventually all energy of the universe will be spread out evenly throughout the universe and everything will be the same temperature – at this point the energy will no longer be able to do work.
The Universe will be ‘dead’
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53. Objective: To consider the energy resources of our world
10.9 Energy and Our World
Objective: To consider the energy resources of our world
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54. Where does our energy ultimately come from?
By the process of photosynthesis plants store energy which then can be converted over millions of years to fossil fuels.
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55. Figure 10.7: Energy sources used in the United States.
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56. Petroleum and Natural Gas
Petroleum and Natural gas is most likely formed from the remains of marine organism that lived more than 500 million years ago
Petroleum is a thick dark liquid composed of hydrocarbons.
Natural Gas consist mostly of methane
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57. Coal
Coal is formed from the remains of plants that were buried and subjected to high pressure and heat over long periods of time.
The energy available from the combustion of coal depends upon the grade of coal. The more carbon in the coal the higher the energy yield.
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58. Coal supplies 20% of our energy in the US What are the problems associated with coal? 1. expensive and dangerous to mine 2. Strip mining of fertile farmland 3. Burning of coal released Sulfur Dioxide. 4. Combustion of coal releases high levels of carbon dioxide, which in turns effects the earths temperature.
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59. Figure 10.8: The earth’s atmosphere.
Approximately 30% of the sun’s energy is reflected back into space by the earths atmosphere.
The remaining energy passes through to the earths surface.
Energy is absorbed by plants and the oceans, soil, rock and water, thus increasing the temperature of the earth’s surface. This energy is radiated from the earths surface as infrared radiation (aka heat radiation).
The atmosphere is transparent to visible light, but does not allow all the infrared radiation to pass back into space (that is, it acts as a greenhouse).
Molecules (principally water and carbon dioxide, strongly absorb infrared radiation and radiate it back to the earth. A net amount of thermal energy is retained, causing the earth to much warmer than it would be without its atmosphere.
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60. Effects of Carbon Dioxide on Climate The Greenhouse Effect
The temperature of the earth is controlled to a significant extend by the CO2 and H2O content of the atmosphere.
Connection: What happened when the production of heat when the moisture in the earths atmosphere increases (humidity)?
In the summer when the humidity is high, the heat of the sun is retained well into the night, giving very high nighttime temperatures.
In winter, the coldest temperatures occur at night when the level of moisture is at its lowest.
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61. Figure 10.9: The atmospheric CO2 concentration over the past 1000 years.
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62. New Energy Sources Solar Nuclear Wind Biomass Synthetic fuels
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63. 10.10 Energy as a Driving Force
Objective: To understand energy as a driving force for natural processes
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64. Why do thing occur? Why do some reactions in nature proceed in a particular direction?
Wood + O2(g) → CO2 (g) + H2) (g) + energy + ashes Why doesn’t the reverse happen?
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65. 2 Factors That are important to Driving Forces
Energy Spread
Matter Spread
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66. Energy Spread
Energy Spread means that in a given process, concentrated energy is dispersed widely.
This distribution always happens every time an exothermic reaction occurs.
The energy that flows into the surroundings through heat increases the thermal motions of the molecules in the surroundings.
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67. Matter Spread
Matter spread says that molecules of a substance are spread out and occupy a large volume.
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68. Entropy (S) is the natural tendency of the world to become disordered.
As randomness increases, S increases.
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69. Figure 10.10: Comparing the entropies of ice and steam.
Which has
Greater entropy?
Ice or steam?
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70. ENERGY SPREAD→ Faster random motions of the molecules in surroundings
What happens to the disorder of the universe as energy spread and matter spread occur during a reaction?
ENERGY SPREAD→ Faster random motions of the molecules in surroundings
MATTER SPREAD → Components of matter are dispersed – they occupy a larger volume.
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71. If energy is conserved, how can there be an “energy crisis”
What is “cracking” of petroleum products? How did it help increase production of gasoline?
What is the greenhouse effect and what are the key molecules that cause it?
What driving force must be predominant for an endothermic reaction to occur? Why?
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