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

• 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:

• 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

• Transition State Theory

  • If the rate constant for a reaction is known, TST can be used successfully to calculate the standard enthalpy of activation, the standard entropy of activation, and the standard Gibbs energy of activation.
  • The species that forms during the transition state is a higher-energy species known as the activated complex.
  • According to collision theory, a successful collision is one in which molecules collide with enough energy and with proper orientation, so that reaction will occur.
  • For instance, by knowing the possible transition states that can form in a given reaction, as well as knowing the various activation energies for each transition state, it becomes possible to predict the course of a biochemical reaction, and to determine its reaction rate and rate constant.

• 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.

• 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.