Browsing by Author "Worswick, Richard D."

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    Thermodynamic Study of Disorder in Hexa-amminenickel(II) Iodide and Diamminenickel(II) Iodide
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (09), 1974) Worswick, Richard D.; Cowell, Janice C.; Staveley, Lionel A. K.
    The heat capacity of crystalline nickel(II) iodide, diamminenickel(II) iodide and hexa-ammine-nickel(II) iodide has been determined from 10 to 300 K by conventional adiabatic low-temperature calorimetry, and from 300 to 550 K by differential scanning calorimetry. Measurements have also been made of (a) the heat of solution of the three salts in dilute acid at 298.15 K, (b) the ammonia dissociation pressure for the systems nickel iodide + diamminenickel iodide (from 490 to 523 K) and diamminenickel iodide + hexa-amminenickel iodide (from 469 to 503 K), (c) the magnetic susceptibility of nickel iodide and diamminenickel iodide from 4 to 230 K. The thermodynamic results have been used to obtain for the diammine and the hexammine two values of the molar entropy at 298.15 K, namely the third-law entropy Scal, and the entropy Seq derived from the appropriate equilibrium study. For each salt, Scal and Seq agree within experimental error, so that both salts appear to become completely ordered at 0 K. The implications of this result for hexa-amminenickel iodide are briefly discussed in the light of previous experimental and theoretical work on this salt.
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    Thermodynamic study of disorder in mercury(II) diamminodichloride and mercury(II) diamminodibromide
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Cooke, Michael D.; Linford, Roger G.; Staveley, Lionel A. K.; Worswick, Richard D.
    In the salts mercury(II) diammino-dichloride and -dibromide the mercury atoms are positionally disordered at room temperature, the disorder being tantamount to that of dimers (the linear NH3—Hg—NH2+3 cations) on a cubic lattice. The heat capacity of the chloride has been measured from 3 to 300 K and that of the bromide from 10 to 300 K, giving the apparent (calorimetric) entropies of the salts at 298.15 K. The true (equilibrium) entropies at the same temperature have been determined by e.m.f. measurements on cells incorporating the complexes in the cell reaction, combined with previous measurements of the heat of solution of gaseous ammonia in the electrolytes used in the cells. A comparison of the entropy values shows that both salts retain entropy, and hence are still disordered, at the absolute zero. The value of the residual entropy for the chloride (considered to be the more accurate of the two) is 12.0 ± 3.0 J K–1 mol–1, and that for the bromide is 20.0 ± 7.5 J K–1 mol–1. These estimates of the residual entropy are briefly considered in the light of theoretical work on the disordered dimer problem. It seems likely that the residual entropy due to the disordered arrangement of the cations is supplemented by some degree of (possibly consequential) orientational disorder of the ammonia molecules.