Examples of free energy in the following topics:
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- 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.
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- 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.
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- 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.
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- 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
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- 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
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- 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.
- Water below zero degrees Celsius undergoes a decrease in its entropy, but the heat released into the surroundings more than compensates for this so the entropy of the world increases, the free energy of the H2O diminishes, and the process proceeds spontaneously.
- 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
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- Spontaneous processes do not require energy input to proceed, whereas nonspontaneous processes do.
- The sign convention of changes in free energy follows the general convention for thermodynamic measurements.
- This means a release of free energy from the system corresponds to a negative change in free energy, but to a positive change for the surroundings.
- An endergonic reaction (also called a nonspontaneous reaction or an unfavorable reaction) is a chemical reaction in which the standard change in free energy is positive, and energy is absorbed.
- The total amount of energy is a loss (it takes more energy to start the reaction than what is gotten out of it) so the total energy is a negative net result.
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- However, if the energy of the light is such that the electron is excited above energy levels associated with the atom, the electron can actually break free from the atom leading to ionization of the atom.
- In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function of the material (the electron binding energy), it is ejected.
- If excess photon energy is absorbed, some of the energy liberates the electron from the atom and the rest contributes to the electron's kinetic energy as a free particle.
- The maximum kinetic energy of an ejected electron is given by
- The maximum kinetic energy of an ejected electron is then
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- 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.
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- 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.