IB Chemistry HL - Option C (Energy)

energy density

energy released from fuel/volume of fuel consumed

specific energy

energy released from fuel/mass of fuel consumed

renewable energy resources

solar energy, wind energy, biomass, water, geothermal energy, and fuel cells

cracking

the process of breaking longer chained hydrocarbons into shorter ones (e.g. ethene, octane) for fuels; this is done over heat, using a catalyst

advantages of cracking

shorter hydrocarbons are better fuels that burn with cleaner flame

octane rating

a measure of a fuel’s ability to resist knocking (auto-ignition)

octane rating of 2,2,4-trimethylpentane

100

octane rating of toluene

114

octane rating of ethanol

113

octane rating of heptane

0

factors that increase octane rating

branching, shorter carbon chain length, isomerization, and being an aromatic/cyclic hydrocarbons

catalytic reforming

the process of converting low-octane rated alkanes to higher-octane isomers, usng heat and a platinum catalyst

coal gasification

the production of synthesis gas by reacting coal with oxygen and steam in a gasifier to create hydrocarbons

carbon capture and storage (css)

capturing carbon dioxide from large industrial processes, compressing it, and transporting it, to be injected deep into rock formations

indirect coal liquification (icl)

the taking of filtered and clean synthesis gas, then adding water or carbon oxide over a catalyst

direct coal liquification (dcl)

the adding of hydrogen to filtered coal in the presence of a catalyst

what is the use of coal liquification

through adjusting the coal to hydrogen ration, synthetic liquid fuels are produced

carbon footprint

a measure of the quantity of carbon dioxide produced by burning fuels

binding energy

the energy required to separate a nucleus into its constituent parts; the higher the binding energy, the more stable the nucleus

nuclear fission

the splitting of elements into lighter nuclei

nuclear fusion

the fusing of elements into heavier nuclei

critical mass

the mass needed for a fuel’s reaction to be self-sustaining

transmutation

the conversion of one element to another by capture or emission of a particle

conjugation

the interaction of alternating double bonds to produce delocalized pi electrons; light can be absorbed by chlorophyll (and other pigments) with a conjugated electronic structure

electron conjugation

multi-center chemical bonding

photosynthesis reaction

6CO2 + 6H2O → C6H12O6 + 6O2

where are biofuels (e.g. ethanol) obtained

from corn sugar or glucose through fermentation

carbon neutral

the making of no net release of carbon dioxide (e.g. biofuels)

biodiesel

fuel produced from vegetable oil

advantages of biodiesel

sustainable/renewable while releasing similar amounts of energy to diesel when burnt; uses waste; lower carbon footprint

disadvantages of biodiesel

highly viscous/can clog fuel injectors; needs transesterification; do not undergo complete combustion, damaging engines

transesterification

involves a reaction of an alcohol in the presence of a strong acid or base; transesterification with ethanol or methanol produces oils with lower viscosity, that can be used in diesel engines

greenhouse gases

a gas (e.g. carbon dioxide, methane, water vapor, nitrogen oxides) that absorbs infrared radiation (IR), contributing to climate change and the greenhouse effect

explain the mechanism by which greenhouse gases absorb infrared radiation

short-wave sunlight waves are absorbed by the upper atmosphere, allowing ultraviolet rays (UV); these UV waves are re-emitted from the surface as longer-wavelength IR; IR interacts with the covalent bonds of greenhouse gases, bending and stretching them

there is a heterogeneous equilibrium between the concentration of [ ] and aqueous [ ] in the oceans

carbon dioxide

sources of greenhouse gas emissions

burning, coal, oil, and natural gas; industrial gases from factories; deforestation

carbon sinks

a natural environment used to absorb carbon dioxide (e.g. forest, ocean)

battery

a series of portable electrochemical cells

primary electrochemical cells

electrochemical cells with materials consumed without being able to reverse the reaction

secondary electrochemical cells/rechargeable batteries

electrochemical cells with chemical reactions that can be reversed through the application of electrical currents and redox reactions

lead-acid batteries

use sulfuric acid electrolyte solutions for a lead anode and lead (II, IV) oxide cathode (PbO4); secondary cells

lead-acid battery reaction

Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O

lead-acid battery advantages

simple and cheap to manufacture

lead-acid battery disadvantages

low energy density, overcharging leads to hydrogen gas and oxygen production, lead is toxic

lithium-ion rechargeable batteries

use lithium atoms absorbed into a lattice of graphite electrode; secondary cells

lithium-ion battery reaction

Li+ (electrolyte) + e- + CoO2 (s) → LiCoO2 (s)

lithium-ion battery advantages

high energy density, lightweight (making them safe for disposal at normal landfill sites, opposed to heavier metal batteries), holds charge better than nickel-cadmium and lead-acid batteries, can withstand many charge cycles

lithium-ion battery disadvantages

sensitive to high temperatures, can be easily damaged if allowed to run flat, lasts only a few years, could possibly explode if overheated

nickel-cadmium (NiCd) rechargeable cells

use nickel (III) oxide cathodes, which reduces to nickel (II) hydroxide; the anode is cadmium, oxidizing to cadmium hydroxide

NiCd reaction

Cd + 2NiO(OH) + 2H2O → 2Ni(OH)2 + Cd(OH)2

NiCd advantages

low internal resistance, allowing for quick recharge time; can undergo a full discharge without damage

NiCd disadvantages

high cost, use of heavy metals are environmentally unfriendly, quickly lose charge at higher temperatures

fuel cell

an electrochemical device that converts chemical potential energy in a fuel into electrical energy; it has an electrolyte that prevents components from mixing, a proton exchange membrane (PEM) that acts as a salt bridge, oxidizing and reducing electrodes, and a bipolar plate

alkali fuel cells

use an electrolyte solution of potassium chloride to convert potential energy into electrical

direct methanol fuel cell

similar to a PEM fuel cells yet uses methanol to provide H+ ions at the anode, rather than hydrogen gas (like in other fuel cells)

thermodynamic efficiency of a fuel cell

the ratio of Gibbs free energy to enthalpy change

Nernst equation

E = E⁰ - (RT/nF)lnQ

[E⁰ is emf, F the Faraday constant/96500 C mol-, and Q the reaction quotient or [ions being oxidized]/[ions being reduced]

Q at stoichiometric equilibrium

[Y]^Y[Z]^Z/[W]^w[X]^X

concentration cell

has the same electrodes in each half-cell but the concentration of the ions in each half-cell is different

microbial fuel cells

convert chemical energy available from a substrate into electricity by anerobic oxidation carried out by microorganisms

enriched uranium

a type of uranium in which the precent composition of uranium-235 has been increased by isotope separation (e.g. the isolation of U-235 from uranium oxide converted to uranium hexafluoride)

photovoltaic cells

made of semiconductors that can absorb photons of light, resulting in electrons being knocked free from atoms, creating voltage

n-type semiconductors

group 15 semiconductors

p-type semiconductors

group 13 semiconductors