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Chemical reactions Gibbs free energy

The thermodynamic function used as the criterion of spontaneity for a chemical reaction is the Gibbs free energy of reaction, AG (which is commonly referred to as the reaction free energy ). This quantity is defined as the difference in molar Gibbs free energies, Gm, of the products and the reactants ... [Pg.415]

STRATEGY We write the chemical equation for the formation of HI(g) and calculate the standard Gibbs free energy of reaction from AG° = AH° — TAS°. It is best to write the equation with a stoichiometric coefficient of 1 for the compound of interest, because then AG° = AGf°. The standard enthalpy of formation is found in Appendix 2A. The standard reaction entropy is found as shown in Example 7.9, by using the data from Table 7.3 or Appendix 2A. [Pg.416]

What Do We Need to Know Already The concepts of chemical equilibrium are related to those of physical equilibrium (Sections 8.1-8.3). Because chemical equilibrium depends on the thermodynamics of chemical reactions, we need to know about the Gibbs free energy of reaction (Section 7.13) and standard enthalpies of formation (Section 6.18). Ghemical equilibrium calculations require a thorough knowledge of molar concentration (Section G), reaction stoichiometry (Section L), and the gas laws (Ghapter 4). [Pg.477]

A catalyst speeds up both the forward and the reverse reactions by the same amount. Therefore, the dynamic equilibrium is unaffected. The thermodynamic justification of this observation is based on the fact that the equilibrium constant depends only on the temperature and the value of AGr°. A standard Gibbs free energy of reaction depends only on the identities of the reactants and products and is independent of the rate of the reaction or the presence of any substances that do not appear in the overall chemical equation for the reaction. [Pg.505]

Redox reactions that have a positive Gibbs free energy of reaction are not spontaneous, but an electric current can be used to make them take place. For example, there is no common spontaneous chemical reaction in which fluorine is a product, and so the element cannot be isolated by any common chemical reaction. It was not until 1886 that the French chemist Henri Moissan found a way to force the... [Pg.629]

Gibbs free energy of reaction The difference in molar Gibbs free energies of the products and reactants, weighted by the stoichiometric coefficients in the chemical equation. [Pg.952]

At constant temperature and pressure, chemical reactions are spontaneous in the direction of decreasing Gibbs free energy. Some reactions are spontaneous because they give off energy in the form of heat (AH<0). Other reactions are spontaneous because they lead to an increase in the disorder of the system (AS>0). Calculations of AH and AS can be used to probe the driving force behind a particular reaction. [Pg.29]

Here (A rG °)j is the standard transformed equilibrium Gibbs free energy for reaction j, which may be obtained from a standard chemical reference source. [Pg.234]

Chemical equilibrium appears to be the most helpful model concept initially to facilitate identification of key variables relevant in determining water-mineral relations and water-atmosphere relations, thereby establishing the chemical boundaries of aquatic environments. Molar Gibbs free energies (chemical potentials) describe the thermodynamically stable state and characterize the direction and extent of processes approaching equilibrium. Discrepancies between predicted equilibrium composition and the data for the actual system provide valuable insight into those cases in which important chemical reactions have not been identified, in which non-equilibrium conditions prevail, or where analytical data for the system are not sufficiently accurate or specific. Such discrepancies are incentive for research and the improvement of existing models. [Pg.3]

Calculating the standard Gibbs free energy of reaction AG° for a given chemical reaction... [Pg.84]

Understand the relationships among Gibbs free energy, chemical potential, reaction quotients (Q), the equilibrium constant, and the saturation index SI). [Pg.33]

In order to determine the equilibrimn constant, we need to be able to compute the Gibbs free energy of reaction AG xn This is dependent on the quantities po) — the chemical potential of pure... [Pg.87]

Entropy may also influence the spontaneity of chemical reactions. In general terms the entropy represents the disorder or randomness associated with a particular process. The Gibbs free energy of reaction includes both the enthalpy and entropy associated with chemical processes, and is defined as... [Pg.22]

Given a sample reaction, aA + bB cC + dD (where uppercase letters are chemical species and lower case letters are stoichiometric coefficients), the Gibbs Free Energy of Reaction (which determines both whether the process can occur spontaneously and how much energy is available to bacteria mediating the reaction) under ambient conditions is given by. [Pg.23]

Having calculated the standai d values AyW and S" foi the participants in a chemical reaction, the obvious next step is to calculate the standard Gibbs free energy change of reaction A G and the equilibrium constant from... [Pg.163]

Chemical equilibrium for a reaction is associated with the change in Gibbs free energy (AG ) ealculated as follows ... [Pg.385]

The importance of the Gibbs free energy and the chemical potential is very great in chemical thermodynamics. Any thermodynamic discussion of chemical equilibria involves the properties of these quantities. It is therefore worthwhile considering the derivation of equation 20.180 in some detail, since it forms a prime link between the thermodynamics of a reaction (AG and AG ) and its chemistry. [Pg.1231]

Why Do We Need to Know This Material The second law of thermodynamics is the key to understanding why one chemical reaction has a natural tendency to occur bur another one does not. We apply the second law by using the very important concepts of entropy and Gibbs free energy. The third law of thermodynamics is the basis of the numerical values of these two quantities. The second and third laws jointly provide a way to predict the effects of changes in temperature and pressure on physical and chemical processes. They also lay the thermodynamic foundations for discussing chemical equilibrium, which the following chapters explore in detail. [Pg.386]

The decrease in Gibbs free energy as a signpost of spontaneous change and AG = 0 as a criterion of equilibrium are applicable to any kind of process, provided that it is occurring at constant temperature and pressure. Because chemical reactions are our principal interest in chemistry, we now concentrate on them and look for a way to calculate AG for a reaction. [Pg.415]

SOLUTION Use Eq. 1 to determine a reaction Gibbs free energy—a thermodynamic quantity—from a cell emf—an electrical quantity. From the chemical equation for the cell reaction (reaction A), we see that n = 2 mol. [Pg.613]

Chemical models of photosynthesis have been used to investigate two types of reactions photosynthesis and photocatalysis. In photosynthetic processes the standard Gibbs free energy of the reaction is positive, and solar energy is utilized to perform work. In photocatalytic processes the free energy is negative and solar energy is used to overcome the activation barrier. [Pg.9]

The ends of a correctly constructed electrochemical circuit measuring electrical potential difference must always have metals or conductors with identical chemical composition. It is usually reached by simple connection of two metals by copper wires. The inclusion between two metal conductors of a third metal conductor according to Volta s law does not change the difference of potentials at the output of a circuit. The difference of potentials in an electrochemical circuit at equilibrium is caused by the change of Gibbs free energy during the appropriate electrochemical reaction ... [Pg.655]


See other pages where Chemical reactions Gibbs free energy is mentioned: [Pg.427]    [Pg.205]    [Pg.541]    [Pg.45]    [Pg.132]    [Pg.32]    [Pg.163]    [Pg.256]    [Pg.38]    [Pg.111]    [Pg.86]    [Pg.181]    [Pg.435]    [Pg.297]    [Pg.834]    [Pg.385]    [Pg.153]    [Pg.163]    [Pg.600]    [Pg.422]    [Pg.614]    [Pg.739]    [Pg.964]    [Pg.60]    [Pg.74]    [Pg.75]    [Pg.79]   
See also in sourсe #XX -- [ Pg.278 , Pg.280 ]




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