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Thermochemical data for the dissociation of gaseous molecules

The basic thermodynamic data for the design of such reactions can be used to assess the dissociation energies for various degrees of dissociation, and to calculate, approximately, the relevant equilibrium constants. One important source of dissociation is by heating molecules to elevated temperatures. The data below show the general trend in the thermal dissociation energies of a number of important gaseous molecules. [Pg.63]

In these examples the entropy change does not vary widely, and the value of the equilibrium constant is mainly determined by the heat of dissociation. It can be concluded, therefore, that nitrogen is one of the most stable diatomic molecules, and that chlorine is the most stable diatomic halogen molecule. [Pg.63]

As further examples of some important polyatomic molecules. [Pg.63]

These data can be used to obtain the value of the equilibrium constant at any temperature and this in turn can be used to calculate the degree of dissociation through the equation for the concentration dependence of the constant on the two species for a single element, the monomer and the dimer, which coexist. Considering one mole of the diatomic species which dissociates to produce 2x moles of the monatomic gas, leaving (1 — x) moles of the diatomic gas and producing a resultant total number of moles of (1 + x) at a total pressure of P atmos, the equation for the equilibrium constant in terms of these concentrations is [Pg.64]

In the case of hydrogen, for example, at a temperature of 2500 K, the equilibrium constant for dissociation has the value, calculated from the thermodynamic relation between the Gibbs energy of formation and the equilibrium constant of 6.356 x 10 4 and hence at a total pressure of 10 2 atmos, the degree of dissociation is 0.126 at 2500 K, which drops to 8.32 x 10 3 at 2000 K. [Pg.64]


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