Gibbs free energy

Examples of Gibbs 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.
  • 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.
  • 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.

• Free Energy and Work

  • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
  • Gibbs energy is the maximum useful work that a system can do on its surroundings when the process occurring within the system is reversible at constant temperature and pressure.
  • 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.
  • 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.

• 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.
  • 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 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.

• 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

• Thermodynamics of Redox Reactions

  • In order to calculate thermodynamic quantities like change in Gibbs free energy $\Delta G$ for a general redox reaction, an equation called the Nernst equation must be used.
  • The relationship between the Gibbs free energy change and the standard reaction potential is:
  • Translate between the equilibrium constant/reaction quotient, the standard reduction potential, and the Gibbs free energy change for a given redox reaction

• Free Energy

  • Free energy, called Gibbs free energy (G), is usable energy or energy that is available to do work.
  • Free energy is called Gibbs free energy (G) after Josiah Willard Gibbs, the scientist who developed the measurement.
  • Gibbs free energy specifically refers to the energy associated with a chemical reaction that is available after accounting for entropy.
  • In other words, Gibbs free energy is usable energy or energy that is available to do work.
  • Exergonic and endergonic reactions result in changes in Gibbs free energy.

• Concentration of Cells

  • In the late 19th century, Josiah Willard Gibbs formulated a theory to predict whether a chemical reaction would be spontaneous based on free energy:
  • Here, ΔG is the change in Gibbs free energy, T is absolute temperature, R is the gas constant, and Q is the reaction quotient.
  • Gibbs' key contribution was to formalize the understanding of the effect of reactant concentration on spontaneity.
  • The change in Gibbs free energy for an electrochemical cell can be related to the cell potential.
  • Therefore, Gibbs' theory is:

• Electron Donors and Acceptors

  • In other words, they correspond to successively smaller Gibbs free energy changes for the overall redox reaction Donor → Acceptor.
  • Organisms that use organic molecules as an energy source are called organotrophs.
  • Some prokaryotes can use inorganic matter as an energy source.
  • This type of metabolism must logically have preceded the use of organic molecules as an energy source.
  • If oxygen is available, it is invariably used as the terminal electron acceptor, because it generates the greatest Gibbs free energy change and produces the most energy.

• Free Energy Changes in Chemical Reactions

  • Thus, if the free energy of the reactants is greater than that of the products, the entropy of the world will increase and the reaction takes place spontaneously.
  • Conversely, if the free energy of the products exceeds that of the reactants, the reaction will not take place.
  • In a spontaneous change, Gibbs energy always decreases and never increases.
  • An important consequence of the one-way downward path of the free energy is that once it reaches its minimum possible value, net change comes to a halt.
  • where ΔG = change in Gibbs free energy, ΔH = change in enthalpy, T = absolute temperature, and ΔS = change in entropy

• 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.