energy

(noun)

A quantity that denotes the ability of a system to do work. It has dimensions of mass × distance²/time², such as 1 kg m2/sec2 = 1 Joule (J).

Related Terms

Examples of energy in the following topics:

  • Pressure and Free Energy

    • Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure.
    • Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings.
    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature.
    • Therefore, Gibbs free energy is most useful for thermochemical processes at constant temperature and pressure.

  • Energy Changes in Chemical Reactions

    • Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.
    • By the Law of Conservation of Energy, however, we know that the total energy of a system must remain unchanged, and that oftentimes a chemical reaction will absorb or release energy in the form of heat, light, or both.
    • The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.
    • This means that the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.
    • This means that the energy required to break the bonds in the reactants is more than the energy released when new bonds form in the products; in other words, the reaction requires energy to proceed.

  • Free Energy and Work

    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • The work is done at the expense of the system's internal energy.
    • Energy that is not extracted as work is exchanged with the surroundings as heat.
    • ΔG is the maximum amount of energy which can be "freed" from the system to perform useful work.

  • Ionization Energy

    • The ionization energy of a chemical species (i.e., an atom or molecule) is the energy required to remove electrons from gaseous atoms or ions.
    • Large atoms or molecules have low ionization energy, while small molecules tend to have higher ionization energies.
    • More generally, the nth ionization energy is the energy required to strip off the nth electron after the first n-1 electrons have been removed.
    • The ionization energy may be an indicator of the reactivity of an element.
    • This video explains the periodic trends in ionization energy....periodicity.

  • Comparison of Enthalpy to Internal Energy

    • Internal energy and enthalpy are both measurements that quantify the amount of energy present in a thermodynamic system.
    • It includes the energy needed to create the system, but excludes the energy needed to displace the system's surrounding or energy displacement due to external forces.
    • Internal energy encompasses both potential and kinetic energy.
    • Because the internal energy encompasses only the energy contained within a thermodynamic system, the internal energy of isolated systems cannot change.
    • Sometimes, measuring the internal energy of a system may be an inaccurate gauge of the change in energy.

  • General Rules for Assigning Electrons to Atomic Orbitals

    • For the excited electron to go back to its original energy, or ground state, it needs to release energy.
    • This separating of electrons into energy units is called quantization of energy because there are only certain quantities of energy that an electron can have in an atom.
    • The energy of the light released when an electron drops down from a higher energy level to a lower energy level is the same as the difference in energy between the two levels.
    • Electrons that are in the first energy level (energy level 1) are closest to the nucleus and will have the lowest energy.
    • Within each energy level, the s orbital is at a lower energy than the p orbitals.

  • Nuclear Binding Energy and Mass Defect

    • Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts: protons and neutrons, or, collectively, the nucleons.
    • The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons.
    • Once mass defect is known, nuclear binding energy can be calculated by converting that mass to energy by using E=mc2.
    • This energy—available as nuclear energy—can be used to produce nuclear power or build nuclear weapons.
    • For elements lighter than iron-56, fusion will release energy because the nuclear binding energy increases with increasing mass.

  • Lattice Energy

    • Lattice energy is a measure of the bond strength in an ionic compound.
    • Lattice energy is an estimate of the bond strength in ionic compounds.
    • as the charge of the ions increases, the lattice energy increases
    • as the size of the ions increases, the lattice energy decreases
    • This tutorial covers lattice energy and how to compare the relative lattice energies of different ionic compounds.

  • Bond Energy

    • Bond energy is the measure of bond strength.
    • These energy values (493 and 424 kJ/mol) required to break successive O-H bonds in the water molecule are called 'bond dissociation energies,' and they are different from the bond energy.
    • The bond energy is the average of the bond dissociation energies in a molecule.
    • Plot of potential energy vs distance between two atoms.
    • The bond energy is energy that must be added from the minimum of the 'potential energy well' to the point of zero energy, which represents the two atoms being infinitely far apart, or, practically speaking, not bonded to each other.

  • Standard Free Energy Changes

    • The standard Gibbs Free Energy is calculated using the free energy of formation of each component of a reaction at standard pressure.
    • These same definitions apply to standard enthalpies and internal energies.
    • In order to make use of Gibbs energies to predict chemical changes, it is necessary to know the free energies of the individual components of the reaction.
    • The energy units will need to be the same in order to solve the equation properly.
    • Calculate the change in standard free energy for a particular reaction.