- 作者: 潘貫
- 作者服務機構: Contribution from the Department of Chemistry, National Taiwan University
- 中文摘要:
(1) The solubility-product of silver tungstate was evaluated from e.m.f. of the cell,
Ag;Ag2WO4(s)∣Na2WO4(x)m ∥KNO3(m)∣AgNO3(3x)m ∣Ag2WO4(s);Ag(+)
∣NaNO3(1-3x)m∥ ∣NaNO3(1-3x)m∣
by extrapolation of the function,
[E-2k log 3-3k log xm] x=0 +3kα√2m=-k log K’s.p.
to x=0. and then to m=0. The solubility-product constants in the temperature range of 20° to 40℃ are expressed by
logKs.p.=-19.627-76.61/T+2.89×10¯2T
(2) The molal heat of solution of silver tungstate was evaluated from the temperature coefficients of In Ks.p. and given by
△ H=350.5+13.233×10¯2T2 (in cal.)
(3) Standard potentials of the Ag;Ag2WO4(s), WO4¯ electrode were evaluated from π°Ag;Ag+-k log Ks.p.. It gives
E°=-0.4660+1.225×10¯3(t-25)-2.17×10¯6(t-25)2
Over this temperature range.
(4) The molal free energy change for the solution of silver tungstate is given by
△ F=350.5+8,880T-0.1324T2 (in cal.)
(5) Thermodynamic Date for the formation of silver tungstate from its elements at 25℃ were evaluated as follows:
△H° △F° △S°
(Kcal./mol) (Kcal./mol) (cal./deg.)
-228.1 -198.5 -99
(6) Standard potentials of the following cells,
Ag;Ag2CrO4(s), CrO4¯(a=1)∥MoO4=(a=1),Ag2MoO4(s);Ag(+) (IIa)
Ag;Ag2CrO4(s),CrO4¯(a=1)∥WO4¯(a=1),Ag2WO4(s);Ag(+) (IIb)
and
Ag;Ag2MoO4(s),MoO4¯(a=1)∥WO4=(a=1),Ag2WO4(s);Ag(+) (IIc)
were obtained by the combination of standard potentials of
(a) Ag;Ag2CrO4(s),CrO4¯ (b) Ag;Ag2MoO4(s),MoO4¯
and
(c) Ag;Ag2WO4(s),WO4¯
electrodes evaluated in my previous and present investigations. It gives
E°=0.1710-9.96×10¯4T+1.531×10¯6T2 (la)
E°=0.3336-2.00×10¯4T+3.167×10¯6T2 (lb)
and E°=0.1626-1.00×10¯4T+1.636×10¯6T2 (lc)
for Cell (IIa), (IIb) and (IIc), respectively.
(7) Thermodynamic Calculations for the exchange reactions,
CrO4=+Ag2MoO4=Ag2CrO4+MoO4¯ (i)
CrO4¯+Ag2WO4=Ag2CrO4+WO4= (ii)
and MoO4=+Ag2WO4=Ag2MoO4+WO4= (iii)
give
△F°=-7,886+45.9T-0.071T2 (2a)
△F°=-15,386+92.2T-0.146T2 (in cal.) (2b)
△F°=-7,499+46.3T-0.076T2 (in cal.) (2c)
△S°=-45.9+0.14T (in cal.) (3a)
△S°=-92.2+0.29T (in cal.) (3b)
△S°=-46.3+0.15T (in cal.) (3c)
△H°=-7,886+0.071T2 (in cal.) (4a)
△H°=-15,386+0.146T2 (in cal.) (4b)
and △H°=-7,499+0.076T2 (in cal.) (4c)
for reactions (iv), (v) and (vi), respectively. - 英文摘要: --
- 中文關鍵字: --
- 英文關鍵字: --