free energy

Examples of free 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.
  • When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force.
  • Therefore, Gibbs free energy is most useful for thermochemical processes at constant temperature and pressure.

• 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.
  • The standard Gibbs free energy of the reaction can also be determined according to:
  • Standard Gibbs free energies of formation are normally found directly from tables.
  • The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of that substance from its component elements, at their standard states.
  • Calculate the change in standard free energy for a particular reaction.

• 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.
  • The appellation "free energy" for G has led to so much confusion that many scientists now refer to it simply as the "Gibbs energy. " The "free" part of the older name reflects the steam-engine origins of thermodynamics, with its interest in converting heat into work.

• Free Energy

  • Free energy, called Gibbs free energy (G), is usable energy or energy that is available to do work.
  • A measurement of free energy is used to quantitate these energy transfers.
  • Free energy is called Gibbs free energy (G) after Josiah Willard Gibbs, the scientist who developed the measurement.
  • In other words, Gibbs free energy is usable energy or energy that is available to do work.
  • A negative ∆G also means that the products of the reaction have less free energy than the reactants because they gave off some free energy during the reaction.

• Free Energy and Cell Potential

  • In a galvanic cell, where a spontaneous redox reaction drives the cell to produce an electric potential, the change in Gibbs free energy must be negative.
  • In a galvanic cell, where a spontaneous redox reaction drives the cell to produce an electric potential, the change in Gibbs free energy must be negative.
  • Calculate the change in Gibbs free energy of an electrochemical cell where the following redox reaction is taking place:
  • Because the change in Gibbs free energy is negative, the redox process is spontaneous.
  • Calculate the change in Gibbs free energy of an electrochemical cell, and discuss its implications for whether a redox reaction will be spontaneous

• ATP: Adenosine Triphosphate

  • Since ATP hydrolysis releases energy, ATP synthesis must require an input of free energy.
  • Exactly how much free energy (∆G) is released with the hydrolysis of ATP, and how is that free energy used to do cellular work?
  • Unless quickly used to perform work, ATP spontaneously dissociates into ADP + Pi, and the free energy released during this process is lost as heat.
  • The Na+/K+ pump gains the free energy and undergoes a conformational change, allowing it to release three Na+ to the outside of the cell.
  • By donating free energy to the Na+/K+ pump, phosphorylation drives the endergonic reaction.

• Activation Energy

  • Activation energy is the energy required for a reaction to occur, and determines its rate.
  • This small amount of energy input necessary for all chemical reactions to occur is called the activation energy (or free energy of activation) and is abbreviated EA.
  • Since these are energy-storing bonds, they release energy when broken.
  • The free energy released from the exergonic reaction is absorbed by the endergonic reaction.
  • Free energy diagrams illustrate the energy profiles for a given reaction.

• Bond Energy

  • Bond energy is the measure of bond strength.
  • Alternatively, it can be thought of as a measure of the stability gained when two atoms bond to each other, as opposed to their free or unbound states.
  • 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.
  • 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.

• Conservation of Mechanical Energy

  • Conservation of mechanical energy states that the mechanical energy of an isolated system remains constant without friction.
  • Conservation of mechanical energy states that the mechanical energy of an isolated system remains constant in time, as long as the system is free of all frictional forces.
  • Though energy cannot be created nor destroyed in an isolated system, it can be internally converted to any other form of energy.
  • The work-energy theorem states that the net work done by all forces acting on a system equals its change in kinetic energy (KE).
  • The total kinetic plus potential energy of a system is defined to be its mechanical energy (KE+PE).

• 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.
  • In this equation, NA is Avogadro's constant; M is the Madelung constant, which depends on the crystal geometry; z+ is the charge number of the cation; z- is the charge number of the anion; e is the elementary charge of the electron; n is the Born exponent, a characteristic of the compressibility of the solid; $\epsilon _o$ is the permittivity of free space; and r0 is the distance to the closest ion.
  • 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.