Thermodynamic Properties of Tungsten Hexachloride and Tungsten Pentachloride
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The decomposition equilibrium of WCl<SUB>6</SUB> in the gas phase and some thermodynamic properties of WCl<SUB>5</SUB> were studied. Electronic spectra of gases produced by sublimation, evaporation and decomposition of these substances were measured. The vapor pressure of WC15 was measured by a Bourdon-type manometer. Absorption bands in gas phase were observed at 39.2, 30.8, 27.0 and 23.2 kK for WCl<SUB>6</SUB>, at 42.6, 36.4, 28.2 and 12.1 kK for WCl<SUB>5</SUB> and at 31.7 kK for W<SUB>2</SUB>Cl<SUB>10</SUB>. It was confirmed from the change of electronic spectra of WCl<SUB>6</SUB> on heating that tungsten hexachloride decomposed above 240°C according to the chemical equation, WCl<SUB>6(g)</SUB> =WCl<SUB>6(g)</SUB> + 1/2 Cl<SUB>2(g)</SUB>. The equilibrium cons-tant of the above reaction was given as log K=-4.46 X 10<SUP>3</SUP>/ T+ 5.66 (240-466°C). The sublima-tion pressure (P<SUB>sub</SUB>) and the evaporation pressure (P<SUB>evap</SUB>) of WCl<SUB>5</SUB> were given by the following equations : log P<SUB>sub</SUB> (atm) - 4.11 x 10<SUP>8</SUP>/ T+ 7.41 (150-251°C), log P<SUB>evap</SUB> (atm) = 2.77 X 10<SUP>3</SUP>/ T+4.85 (251-287°C). The equilibrium constant of the reaction, W<SUB>2</SUB>Cl<SUB>10(g)</SUB> = 2 WCl<SUB>6(g)</SUB> was given as log K= -1.35 x 10<SUP>3</SUP>/ T+ 3.47 (256-480°C). From these results, the following thermodynamic values were obtained;ΔG<SUP>9</SUP>dec, =20.4X 10<SUP>3</SUP>-25.9T cal/mol, zilidec=- 20.4 kcal/mol and ΔSdec=25.9 cal/deg mol for the reaction, WCl<SUB>6(g)</SUB> =WCl<SUB>5(g)</SUB>+1- 1/2 Cl<SUB>2(G)</SUB>Δ ; G<SUP>0</SUP>sub = 18.8x10<SUP>3</SUP>-33.9T cal/mol, ΔH<SUB>sub</SUB>= 18.8 kcal/mol and ΔS<SUB>sub</SUB>= 33.9 cal/deg.mol for the reaction, WCl<SUB>5(g)</SUB> = WCl<SUB>5(g)</SUB> ; ΔG<SUP>0</SUP><SUB>evap</SUB> = 12.7X10<SUP>3</SUP>- 22.2 T cal/mol, ΔH<SUB>evap</SUB>= 12.7 kcal/mol and ΔS<SUB>evap</SUB>= 22.2 cal/deg. mol for the reaction, WCl<SUB>5(g)</SUB> = WCl<SUB>5(g)</SUB> and ΔG<SUB>diss</SUB>= 6.18 X 10<SUP>3</SUP>-15.9T cal/mol, ΔH<SUB>diss</SUB>= 6.18 cal/mol and ΔS<SUB>diss</SUB>= 15.9 cal/deg.mol for the reaction, W<SUB>2</SUB>Cl<SUB>10(g)</SUB> = 2 WCl<SUB>5(g)</SUB>.
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