Thermodynamics thermochemical equation

Our goal in this chapter is to help you learn the laws of thermodynamics, especially the concepts of entropy and free energy. It might be helpful to review Chapter 6 on thermochemistry and the writing of thermochemical equations. The concept of Gibbs free energy (G) will be useful in predicting whether or not a reaction will occur spontaneously. Just like in all the previous chapters, in order to do well you must Practice, Practice, Practice. 

Al(s) + Fe203(s) —> Al203(s) + 2Fe(l). thermochemical equation An expression consisting of both the balanced chemical equation and the reaction enthalpy for the chemical reaction exactly as written, thermochemistry The study of the heat released or absorbed by chemical reactions a branch of thermodynamics. 

Some Thermodynamic Terms 15-3 Enthalpy Changes 15-4 Calorimetry 15-5 Thermochemical Equations 15-6 Standard States and Standard Enthalpy Changes Standard Molar Enthalpies of... 

The coefficients in a balanced thermochemical equation refer to the numbers of moles of reactants and products involved. In the thermodynamic interpretation of equations we never interpret the coefficients as numbers of molecules. Thus, it is acceptable to write coefficients as fractions rather than as integers, when necessary. 

Thermochemical equation A balanced chemical equation together with a designation of the corresponding value of Sometimes used with changes in other thermodynamic quantities. 

Any thermodynamic quantity such as AH that is associated with a thermochemical equation always refers to the number of moles of substances explicitly shown in the equation. Thus for the synthesis of water we can write... 

Thermal pollution. The heating of the environment to temperatures that are harmful to its living inhabitants. (12.4) Thermochemical equation. An equation that shows both the mass and enthalpy relations. (6.3) Thermochemistry. The study of heat changes in chemical reactions. (6.2) Thermodynamics. The scientific study of the interconversion of heat and other forms of energy. (6.7)... 

The heats of formation of various ionic compounds show tremendous variations. In a general way, we know that many factors contribute to the over-all heat of formation, namely, the ionization potentials, electron affinities, heats of vaporization and dissociation of the elements, and the lattice energy of the compound. The Born-Haber cycle is a thermodynamic cycle that shows the interrelation of these quantities and enables us to see how variations in heats of formation can be attributed to the variations in these individual quantities. In order to construct the Born-Haber cycle we consider the following thermochemical equations, using NaCl as an example... 

Surroundings, 160 System. 160 Thermal energy, 160 Thermochemical equation, 170 Thermochemistry. 161 Thermodynamics, 163... 

State of a system, 176 Surroundings, 172 System, 172 Thermal energy, 172 Thermochemical equation, 182 Thermochemistry, 173 Thermodynamics, 176... 

Ekjuations of the forms (a), (b), and (c) are called thermochemical equations. Generally, these kinds of equations can be added, subtracted, reversed and multiplied by constants. Thus, it is possible to obtain information of changes of enthalpy for processes for which no thermodynamic data are available, or of processes for which experimental investigations are difficult. 

Heat Capacity, C° Heat capacity is defined as the amount of energy required to change the temperature of a unit mass or mole one degree typical units are J/kg-K or J/kmol-K. There are many sources of ideal gas heat capacities in the hterature e.g., Daubert et al.,"" Daubert and Danner,JANAF thermochemical tables,TRC thermodynamic tables,and Stull et al. If C" values are not in the preceding sources, there are several estimation techniques that require only the molecular structure. The methods of Thinh et al. and Benson et al. " are the most accurate but are also somewhat complicated to use. The equation of Harrison and Seaton " for C" between 300 and 1500 K is almost as accurate and easy to use ... 

There is another use of the Kapustinskii equation that is perhaps even more important. For many crystals, it is possible to determine a value for the lattice energy from other thermodynamic data or the Bom-Lande equation. When that is done, it is possible to solve the Kapustinskii equation for the sum of the ionic radii, ra + rc. When the radius of one ion is known, carrying out the calculations for a series of compounds that contain that ion enables the radii of the counterions to be determined. In other words, if we know the radius of Na+ from other measurements or calculations, it is possible to determine the radii of F, Cl, and Br if the lattice energies of NaF, NaCl, and NaBr are known. In fact, a radius could be determined for the N( )3 ion if the lattice energy of NaNOa were known. Using this approach, which is based on thermochemical data, to determine ionic radii yields values that are known as thermochemical radii. For a planar ion such as N03 or C032, it is a sort of average or effective radius, but it is still a very useful quantity. For many of the ions shown in Table 7.4, the radii were obtained by precisely this approach. 

This point of tangency can be determined, assuming that the equation of state P = P( V, E) of the products is known. The chemical composition of the products changes with the thermodynamic state, so thermochemical codes must solve for state variables and chemical concentrations simultaneously. This problem is relatively straightforward, given that the equation of state (EOS) of the fluid and solid products are known. 

Exp-6 potential models can be validated through several independent means. Fried and Howard33 have considered the shock Hugoniots of liquids and solids in the decomposition regime where thermochemical equilibrium is established. As an example of a typical thermochemical implementation, consider the Cheetah thermochemical code.32 Cheetah is used to predict detonation performance for solid and liquid explosives. Cheetah solves thermodynamic equations between product species to find chemical equilibrium for a given pressure and temperature. From these properties and elementary detonation theory, the detonation velocity and other performance indicators are computed. 

Thermodynamically-Controlled Reaction. A chemical reaction which has gone all the way to completion, and the ratio of different possible products is related to their thermochemical stabilities according to the Boltzmann Equation. 

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