chapter 04 energy

8/11/2019 Chapter 04 Energy

1/22


2/22

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


3/22

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


4/22


5/22

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


6/22


7/22

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


8/22

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


9/22


10/22

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)


11/22


12/22

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


13/22

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


14/22

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



15/22

Advantages Liquid; Easily pumped and transported More concentrated energy source than coal

Disadvantages Must be processed since its a mixture


16/22

Increasing the Amount of Gasolinefrom Petroleum Mixture

Cracking Reactions Catalytic Recombination


Cracking Kerosene Molecules to Form Gasoline- sized Molecules

C16H34

C8H18 C8H16+


17/22

Octane Rating Describe the Amount ofKnocking a Fuel Undergoes When it is Burned


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


18/22

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



19/22

Alternative Fuels and Alternative EnergySources



20/22

Direct Burning

Conversion



21/22

BioGas Digester



22/22

chapter 04 energy

Documents