energy density

Examples of energy density in the following topics:

• The Lithium-Ion Battery

  • They are one of the most popular types of rechargeable battery for portable electronics because they have one of the best energy densities and only a slow loss of charge when not in use.
  • Research is yielding a stream of improvements to traditional LIB technology, focusing on energy density, durability, cost, and safety.
  • Handheld electronics mostly use LIBs based on lithium cobalt oxide (LCO), which offer high energy density but have well-known safety concerns, especially when damaged.
  • Lithium iron phosphate (LFP), lithium manganese oxide (LMO), and lithium nickel manganese cobalt oxide (LiNMC) batteries offer lower energy density but longer lives and inherent safety.
  • When a lithium-based cell is discharging, the positive lithium ion is extracted from the cathode and inserted into the anode, releasing stored energy in the process.

• The Hydrogen Economy

  • As such, hydrogen is not a primary energy source, but an energy carrier.
  • As a potential fuel, hydrogen is appealing because it has a high energy density by weight.
  • Fuel cells are electrochemical devices capable of transforming chemical energy into electrical energy.
  • Although H2 has high energy density based on mass, it has very low energy density based on volume.
  • Increasing the gas pressure will ultimately improve the energy density by volume, but this requires a greater amount of energy be expended to pressurize the gas.

• Bonding and Antibonding Molecular Orbitals

  • Atomic orbital energy correlates with electronegativity, as electronegative atoms hold electrons more tightly, lowering their energies.
  • MO modeling is only valid when the atomic orbitals have comparable energy; when the energies differ greatly, the bonding mode becomes ionic.
  • Two same-sign orbitals have a constructive overlap, forming a molecular orbital with the bulk of the electron density located between the two nuclei.
  • Atomic orbitals can also interact with each other out-of-phase, leading to destructive cancellation and no electron density between the two nuclei.
  • Whenever symmetry or energy make mixing an atomic orbital impossible, a non-bonding MO is created; often quite similar to and with energy levels equal or close to its constituent AO, the non-bonding MO creates an unfavorable energy event.

• Supercritical Fluids

  • This can be rationalized by thinking that at high enough temperatures (above the critical temperature) the kinetic energy of the molecules is high enough to overcome any intermolecular forces that would condense the sample into the liquid phase.
  • Since density increases with pressure, solubility tends to increase with pressure.
  • At constant density, solubility will increase with temperature.
  • Other properties, such as density, can also be calculated using equations of state.
  • The system consists of 2 phases in equilibrium, a dense liquid and a low density gas.

• Crystal Field Theory

  • Therefore, the d electrons closer to the ligands will have a higher energy than those further away, which results in the d orbitals splitting in energy.
  • All of the d orbitals have four lobes of electron density, except for the dz2 orbital, which has two opposing lobes and a doughnut of electron density around the middle.
  • On the other hand, the lobes of the dxy, dxz, and dyz all line up in the quadrants, with no electron density on the axes.
  • For example, in the case of an octahedron, the t2g set becomes lower in energy.
  • Conversely, the eg orbitals are higher in energy.

• Recycling and Disposal

  • Thus, instead of consigning all plastic trash to a land fill, some of it may provide energy by direct combustion, and some converted for reuse as a substitute for virgin plastics.
  • The energy potential of plastic waste is relatively significant, ranging from 10.2 to 30.7MJkgÃ1, suggesting application as an energy source and temperature stabilizer in municipal incinerators, thermal power plants and cement kilns.
  • The use of plastic waste as a fuel source would be an effective means of reducing landfill requirements while recovering energy.
  • When placed in a medium of intermediate density, particles of different densities separate-lower density particles float while those of higher density sink.
  • Various separation media have been used, including water or water solutions of known density (alcohol, NaCl, CaCl2 or ZnCl2).

• Changes in Energy

  • The concept of entropy can be described qualitatively as a measure of energy dispersal at a specific temperature.
  • This is because some energy is expended as heat, limiting the amount of work a system can do.
  • In a thermodynamic system, pressure, density, and temperature tend to become uniform over time because this equilibrium state has a higher probability (more possible combinations of microstates) than any other.
  • This is because the thermal energy from the warm surroundings spreads to the cooler system of ice and water.
  • The entropy of the room decreases as some of its energy is dispersed to the ice and water.

• Single Covalent Bonds

  • There are four hierarchical levels that describe the position and energy of the electrons an atom has.
  • Principal energy levels are made out of sublevels, which are in turn made out of orbitals, in which electrons are found.
  • This is referred to as "electron density."
  • Covalent bonding occurs when two atomic orbitals come together in close proximity and their electron densities overlap.

• Properties of Sulfur

  • Again, this is accompanied by a lower density but increased viscosity due to the formation of polymers.
  • The density of sulfur is about 2 g/cm3, depending on the allotrope.
  • The first and the second ionization energies of sulfur are 999.6 and 2252 kJ/mol, respectively.
  • The fourth and sixth ionization energies are 4556 and 8495.8 kJ/mol.

• Properties of Aromatic Compounds

  • Aromatic compounds are ring structures with delocalized $\pi$ electron density that imparts unusual stability.
  • However, the bonding is stronger than expected for a conjugated structure, and it is more accurately depicted as delocalized electron density shared between all the atoms in the ring.
  • Aromatic compounds are cyclic structures in which each ring atom is a participant in a$\pi$ bond, resulting in delocalized $\pi$ electron density on both sides of the ring.
  • This delocalization leads to a lower overall energy for the molecule, giving it greater stability.