Download - Chapter 04 Energy
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Defini t ions
Energy the capacity to do work Work is done when movement occurs against a restraining force.
The force multiplied by the distance Heat is energy that flows from a hotter to a colder object.
Temperature is a measure of the heat content of an object. Both work and heat are forms of molecular motion
Work is organized motion (all the molecules moving in the samedirection)
Heat is random motion (all the molecules moving in differentdirections)
Energy is the sum of all these molecular motions
Energy is neither created nor destroyed Conservation of Energy Conservation of Mass
Energy can be converted from one form into another
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Energy Transformations
Can we get complete energy conversion?Efficiency measures the ability of an engine to transform chemical energy to mechanicalenergy
Efficiencies are multiplicativee.g. Overall efficiency = efficiency of (power plant) x (boiler) x (turbine) x (electrical generator)
x (power transmission) x (home electric heater)
Overall efficiency = efficiency of (power plant) x (boiler) x (turbine) x(electrical generator) x (power transmission) x (home electric heater)
Overall efficiency = .60 x .90 x .75 x .95 x .98Overall efficiency = 0.3434 % energy generated is usedThe rest is wasted
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CH 4(g) + 2 O 2(g) CO 2(g) + 2 H 2O(g) + energy Heat of combustion of methane is -50.1 kJ/g
For every gram of methane burned we get 50.1 kJ energy
For every mole of methane burned we get 802.3 kJenergy
The combustion of one mole of methane will always produce one mole of carbon dioxide, two moles of water,and 802.3 kilojoules of heat energy
44
4 4
16.0 50.11 802.3
1 1
g CH kJ mol CH kJ
mol CH g CH
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Chem is t ry Discu ss ion
Chemical reactions involve the rearrangement of atomsand bonds Breaking the bonds of reactants Moving atoms around
Creating the bonds of products It takes energy to break bonds
Endothermic (process that absorbs energy)
It releases energy to form bonds Exothermic (processes that release energy) The difference between the energy required to break
the bonds of the reactants and to make the bonds of the products is the heat of reaction
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CH 4(g) + 2 O 2(g) CO 2(g) + 2 H 2O(g)Reactants
Methane (4 C-H bonds)
Oxygen (2 molecules, each with an O=O double bond)Products
Carbon dioxide (2 C=O double bonds)Water (2 molecules, each with 2 H-O bonds)
Energy is released because there is energy left overEnergy of reactants > Energy of products
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Formation of Water, Clean Combustion Better Society
2 H 2(g) + O 2(g) 2 H 2O(g) + energyReactants
Hydrogen (2 molecules, each with 1 H-H bond)Oxygen (one O=O double bond)
Products
Water (2 molecules, each with 2 H-O bonds)
Energy is released because there is energy left over
872 kJ + 498 kJ 1868 kJ = 498 kJ (exothermic)
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Fossil Fuels (Coal, Petroleum, Natural Gas)
Formed over long periods of time from the remainsof plants and animals under layers of sedimentaryrock
Nonrenewable Resource Fossils fuels are derived from organic compounds Organic Compounds Made mostly of C and H; but
can contain small amounts of O, N, S, P, X
Energy, Chemistry, and Society
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CoalEnergy, Chemistry, and Society
Disadvantages1. Difficult to Transport Since
its a Solid 2. Combustion products; CO 2,
SOx, NO
x, precursor to acid
rain formation
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Petroleum: Distillation Separates the Components of Crude Oil Mixture
As the number of carbons in petroleum substance increase; boiling point increases
Distillation separates petroleum mixture by different boiling points
Energy, Chemistry, and Society
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Advantages Liquid; Easily pumped and transported More concentrated energy source than coal
Disadvantages Must be processed since its a mixture
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Increasing the Amount of Gasolinefrom Petroleum Mixture
Cracking Reactions Catalytic Recombination
Energy, Chemistry, and Society
Cracking Kerosene Molecules to Form Gasoline- sized Molecules
C16H34
C8H18 C8H16+
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Octane Rating Describe the Amount ofKnocking a Fuel Undergoes When it is Burned
Energy, Chemistry, and Society
heptane
CH 2 CH 2CH 2CH 2 CH 2CH 3 CH 3
CCH 3
CH 3
CH 3
CH 2 CH
CH 3
CH 3
Isooctane
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Society, Reasons to Reduce
Burning Fossil Fuels
1. Greenhouse Gas Production2. Air Pollution / Acid Rain3. Compounds in Petroleum are the needed raw
materials to make many compounds plastics, pesticides, pharmaceuticals, fertilizers, etc
4. Fossil Fuels are Nonrenewable Resources
Energy, Chemistry, and Society
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Alternative Fuels and Alternative EnergySources
Energy, Chemistry, and Society
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Direct Burning
Conversion
Energy, Chemistry, and Society
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BioGas Digester
Energy, Chemistry, and Society
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