Ammonia formation enthalpy

Mass effects due to some ions in salts. It is generally observed that there is a greater instability amongst compounds containing heavy atoms compared with elements in the first periods of the periodic tabie.This can be observed by analysing enthalpies of formation of ammonia, phosphine, arsine and stibine (see previous table for the last three). In the same way, it is easier to handle sodium azide than lead azide, which is a primary explosive for detonators. It is exactly the same with the relatively highly stable zinc and cadmium thiocyanates and the much less stable mercury thiocyanate. 

Alternatively, the translational energy threshold for endothermic proton transfer from MH+ to R can be measured using a flowing afterglow triple quadrupole instrument.127 These data define the proton affinity of M, relative to that of R. Thus, the PA of cyclopropenylidene was found to exceed that of ammonia by 23.3 1.8 kcal/mol (Table 6).128 In order to obtain absolute proton affinities, the enthalpies of formation of both the base and the conjugate acid must be known from other measurements (Eq. 9). Numerous reference compounds with known absolute PA are available.124... 

STRATEGY The synthesis of ammonia is exothermic, so we expect the equilibrium constant to be smaller at the higher temperature. To use the van t Hoff equation, we need the standard reaction enthalpy, which can be calculated from the standard enthalpies of formation in Appendix 2A. 

Flowing ammonia has been applied to the synthesis of the nitrides of iron, cobalt, and nickel compounds with very low enthalpies of formation (Table 2). Again, isothermal conditions were employed. Ammonia is preferable over the use of molecular nitrogen to nitride... 

Figure 2 Volcano plots illustrating how catalytic activities depend on the nature of the metal used as catalyst, (a) Correlation between catal)hic activity for formic acid dehydrogenation and enthalpy of formation of metal formates. (Ref 10. Reproduced by permission of John Wiley Sons, Inc.) (b) Correlation between catal)hic activity for ammonia synthesis and degree of d-band fiUing in the metal used as catalyst. (Ref 12. Reproduced by permission of John Wiley Sons, Inc.) ...

Using the standard enthalpies of formation listed in Table 9.4, calculate the standard enthalpy change for the overall reaction that occurs when ammonia is burned in air to form nitrogen dioxide and water. This is the first step in the manufacture of nitric acid. 

Use the following standard enthalpies of formation to estimate the N—H bond energy in ammonia. Compare this with the value in Table 13.6. 

The enthalpy of formation of Na2Se(cr) was determined to be Af//°(Na2Se, cr, 265 K) = -343.1 kJ-mol by Mulder and Schmidt [51MUL/SCH] using solution calorimetry in liquid ammonia. The value is reasonably close to Af//°(Na2Se, cr,... 

Ammonia is being decomposed and hydrogen fluoride produced. Fluorine and nitrogen are elements in their standard states, and so have zero enthalpies of formation. By using data from Appendix III, and equation 2.10, we may write ... 

The resulting ionic compound is a white solid which melts between 373 and 375 °C (and decomposes to the imide and ammonia above this upper limit as noted above, eventually decomposing to lithium nitride). Experimentally, the standard enthalpy of formation for lithium amide, AHf, is -176 kJ mol ... 

The absorption of ammonia into MgCl2 proceeds in three steps as shown in reactions (19.2)-(19.4), each with a different enthalpy of formation. The formation of Mg(NH3)6Cl2 from MgCl2 and NH3 releases 64kJ/mol NH3. 

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