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17 Stability Constants, Enthalpies, and Entropies of Plutonium(III) and Plutonium(IV) Sulfate Complexes K. L. NASH and J. M. CLEVELAND
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U.S. Geological Survey, Denver, CO 80225
The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1:1 and 1:2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSO+ for the 1:1 complexes of both plutonium(III) and plutonium(IV). The second HSO ligand appears to be added without deprotonation in both systems to form complexes of the form PuSO HSO +. n (2 -)
4
-
4
(n-3)
4
4
P r e d i c t i o n o f the chemistry of plutonium i n near-neutral aqueous m e d i a i s h i g h l y d e p e n d e n t o n u n d e r s t a n d i n g r e a c t i o n s t h a t may b e o c c u r r i n g i n s u c h m e d i a . One o f t h e most i m p o r t a n t param e t e r s i s t h e s t a b i l i t y a n d n a t u r e o f c o m p l e x e s f o r m e d by p l u t o n i u m i n i t s f o u r common o x i d a t i o n s t a t e s . Because P u ( I I I ) , P u ( I V ) , and Pu(VI) a r e r e a d i l y hydrolysed, complexation r e a c t i o n s g e n e r a l l y are s t u d i e d i n m i l d l y t o s t r o n g l y a c i d i c media. Data determined i n a c i d media (and f r e q u e n t l y a t h i g h c o n c e n t r a t i o n s o f plutonium) then a r e used t o p r e d i c t t h e c h e m i c a l s p e c i a t i o n o f p l u t o n i u m a t n e a r - n e u t r a l pH a n d l o w c o n c e n t r a t i o n s o f t h e m e t a l i o n . S e v e r a l p o t e n t i a l l y important ground-water complexing l i g a n d s e x i s t predominantly as protonated s p e c i e s i n a c i d i c media, w h i l e t h e y a r e c o m p l e t e l y i o n i z e d a t pH 7. A n example o f one s u c h system i s t h e s u l f a t e - b i s u l f a t e system. A t pH P u S O ^ " ^ + H
+
(1)
I n a n a t t e m p t t o v e r i f y ( o r r e f u t e ) t h i s a s s u m p t i o n , we have de t e r m i n e d t h e t h e r m o d y n a m i c p a r a m e t e r s (ΔΗ, AS) f o r t h e c o m p l e x e s formed b e t w e e n P u ( I I I ) , P u ( I V ) , and HSO^ i n 1 M a c i d m e d i a u t i l i z i n g c a t i o n - e x c h a n g e and s o l v e n t e x t r a c t i o n p r o c e d u r e s .
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Experimental Reagents. A l l r e a g e n t s used i n t h i s s t u d y were of r e a g e n t g r a d e o r b e t t e r and w e r e p u r i f i e d f u r t h e r by t h e f o l l o w i n g p r o c e d u r e s . T h e n o y l t r i f l u o r o a c e t o n e (TTA) was r e c r y s t a l l i z e d t w i c e f r o m c y c l o h e x a n e and p r o t e c t e d f r o m l i g h t and a i r a f t e r r e c r y s t a l lization. H y d r o q u i n o n e ( h o l d i n g r e d u c t a n t f o r p l u t o n i u m ( I I I ) ) was p u r i f i e d by vacuum s u b l i m a t i o n and a l s o p r o t e c t e d f r o m l i g h t and air after sublimation. S t o c k s o l u t i o n s o f ^ S O i i and HClO^ w e r e p r e p a r e d f r o m U l t r e x (_7) u l t r a p u r e r e a g e n t s . B o t h Na2S0i+ and NaClO^ were r e c r y s t a l l i z e d from d e i o n i z e d w a t e r . Toluene used i n t h e s o l v e n t e x t r a c t i o n w o r k was d i s t i l l e d p r i o r t o u s e , and a l l aqueous s o l u t i o n s w e r e p r e p a r e d i n t r i p l y - d i s t i l l e d w a t e r . In the c a t i o n - e x c h a n g e s t u d y o f P u ( I I I ) c o m p l e x a t i o n , Dowex AG50X2 (20 t o 50 mesh) c a t i o n - e x c h a n g e r e s i n was u s e d , a f t e r b e i n g s u b j e c t e d t o an e x t e n s i v e c l e a n i n g p r o c e d u r e , i n c l u d i n g w a s h i n g w i t h 15% H 0 i n 1 M NaOH, a c e t o n e , and 6 M HC1. Following a distilled-water wash t o remove a l l t r a c e s o f a c i d , t h e r e s i n was d r i e d a t room t e m p e r a t u r e u n d e r m i l d vacuum and s t o r e d i n a d e s i c c a t o r . 2
2
Procedures S t a b i l i t y c o n s t a n t s o f t h e c o m p l e x e s formed between P u ( I I I ) , P u ( I V ) , and HSO^ were d e t e r m i n e d i n 1 M a c i d m e d i a by m e a s u r i n g the decrease i n e x t r a c t i o n ( e i t h e r i n t o TTA-toluene or i o n e x c h a n g e r e s i n ) w i t h i n c r e a s i n g c o n c e n t r a t i o n o f HS0I+ i n t h e aqueous s o l u t i o n . Because of v e r y d i f f e r e n t degrees of e x t r a c t i o n f o r P u ( I I I ) and P u ( I V ) and t h e imposed r e q u i r e m e n t o f 1 M a c i d i t y , P u ( I V ) - H S 0 i 4 _ c o m p l e x a t i o n was s t u d i e d by TTA e x t r a c t i o n , w h i l e t h e P u i l l ^ - H S O ^ s y s t e m was s t u d i e d by c a t i o n e x c h a n g e . S t o c k s o l u t i o n s o f Na2S0i+ and N a C l O ^ were p r e p a r e d by w e i g h t and s t a n d a r d i z e d by p a s s i n g s e v e r a l a l i q u o t s t h r o u g h a bed o f Dowex AG50X8 ( H f o r m ) r e s i n and t i t r a t i n g t h e g e n e r a t e d a c i d w i t h s t a n d a r d i z e d NaOH. S t o c k s o l u t i o n s o f H 2 S O 4 and H C I O 4 w e r e s t a n d a r d i z e d by t i t r a t i o n w i t h NaOH. I n t h e s o l v e n t e x t r a c t i o n s t u d y , TTA s o l u t i o n s w e r e p r e p a r e d by w e i g h t and p r e - e q u i l i b r a t e d w i t h 1.0 M HCIO^ f o r a t l e a s t 24 h o u r s p r i o r t o u s e . The p l u t o n i u m s t o c k s o l u t i o n s w e r e p r e p a r e d by d i s s o l v i n g 99.1% p u r e PuO (0.9% P u O ) i n HNO3-HF s o l u t i o n . A l i q u o t s of t h i s s t o c k w e r e r e p e a t e d l y t a k e n t o n e a r - d r y n e s s i n HClOi+ and +
2 3 9
2 I + 0
2
2
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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17.
NASH AND CLEVELAND
253
Stability Constants
f i n a l l y d i s s o l v e d i n 0.5 M HClOi*. T h i s s o l u t i o n t h e n was e l e c t r o l y t i c a l l y r e d u c e d t o P u ( I I I ) a n d made c h e m i c a l l y p u r e by l o a d i n g o n t o a c o l u m n o f AG5DX2 r e s i n and w a s h i n g w i t h 0.5 M H C I O 4 . To p r e p a r e P u ( I I I ) s t o c k s , t h e p l u t o n i u m was e l u t e d f r o m t h e column w i t h 3 M HC1. Foif t h e p r e p a r a t i o n o f P u ( I V ) s t o c k s , e l u t i o n was performed w i t h 8 M HNO3. T h i s e l u t r i a n t t h e n was made up t o 0.1 M i n NaN02 and a l l o w e d t o e q u i l i b r a t e o v e r n i g h t . O x i d a t i o n - s t a t e p u r i t y was g r e a t e r t h a n 99% i n e a c h c a s e , a s d e t e r m i n e d by 0.5 M TTA e x t r a c t i o n f r o m 1.0 M HCIO^. The P u ( I I I ) - H S 0 ^ s t a b i l i t y c o n s t a n t s w e r e d e t e r m i n e d a t 2.7, 10.0, 1 6 . 5 , and 25.0°C u s i n g t h e f o l l o w i n g p r o c e d u r e . A p p r o x i m a t e l y 1 gram o f AG50X2 r e s i n was i n t r o d u c e d i n t o e a c h o f 22 polyethylene v i a l s . F i v e mL ( m i l l i l i t e r s ) o f 1.0 M HCIO^ (2 M i o n i c s t r e n g t h ) s o l u t i o n s c o n t a i n i n g 0.0 t o 1.0 M H 2 S O 4 w e r e p i p e t t e d i n t o e a c h o f t h e v i a l s (two b l a n k v i a l s and 20 d i f f e r e n t concentrations of H2SO4). F i v e h u n d r e d pL ( m i c r o l i t e r s ) o f 0.1 M h y d r o q u i n o n e w e r e added t o e a c h , w i t h enough P u ( I I I ) f o r a t o t a l c o n c e n t r a t i o n o f 3.3 χ 10 M. T h e s e v i a l s w e r e capped and m i x e d on a r o t a t i n g m i x e r i n a w a t e r b a t h f o r 24 t o 48 h o u r s . After e q u i l i b r i u m was a c h i e v e d , d u p l i c a t e 1.0-mL s a m p l e s o f t h e aqueous phase were t a k e n and counted by l i q u i d s c i n t i l l a t i o n . Replicate d e t e r m i n a t i o n s w e r e done a t e a c h t e m p e r a t u r e . I n a d d i t i o n , one e x p e r i m e n t was c o n d u c t e d u s i n g t h e same p r o c e d u r e w i t h s o l u t i o n s a t 2.0 M a c i d i t y . I n t h e P u ( I V ) d i s t r i b u t i o n e x p e r i m e n t s , 1.0 mL o f e a c h p h a s e was c o n t a c t e d i n a g l a s s c u l t u r e t u b e . Ten y L o f 1.0 M NaNÛ2 and 10 y L o f t h e P u ( I V ) s t o c k w e r e added t o t h e aqueous p h a s e t o g i v e t o t a l c o n c e n t r a t i o n s o f 0.01 M N a N 0 , 0.074 M H N 0 , and 1.8 χ ΙΟ"" M p l u t o n i u m . The p h a s e s w e r e m i x e d v i g o r o u s l y f o r 2 m i n u t e s , c e n t r i f u g e d , and a l l o w e d t o e q u i l i b r a t e i n a c o n s t a n t - t e m p e r a t u r e ( 1 0 . 0 , 2 5 . 0 , a n d 35.0°C) w a t e r b a t h o v e r n i g h t ; a t 0.0°C, e q u i l i b r a t i o n was f o r 5 d a y s . P r e l i m i n a r y experiments i n d i c a t e d that e q u i l i b r i u m was a c h i e v e d i n t h i s t i m e . Two h u n d r e d m i c r o l i t e r s a m p l e s w e r e t a k e n f r o m e a c h p h a s e and c o u n t e d by l i q u i d s c i n t i l l a t i o n , t o a n a v e r a g e c o u n t i n g e r r o r o f 1 t o 3%. A t t h e TTA c o n c e n t r a t i o n s u s e d i n t h e s e e x p e r i m e n t s ( 0 . 0 1 t o 0.05 Μ ) , no q u e n c h i n g o f t h e l i q u i d s c i n t i l l a t i o n by TTA was o b s e r v e d . Two s e t s o f experiments were conducted a t each temperature. The f i r s t s e t was to determine t h e s o l v e n t e x t r a c t i o n e q u i l i b r i u m f o r t h e Pu(IV)-TTA system. I n t h e second s e t o f experiments, a c o n s t a n t c o n c e n t r a t i o n o f TTA was e q u i l i b r a t e d w i t h a s e r i e s o f aqueous s o l u t i o n s a t 1 M a c i d i t y , 2 M i o n i c s t r e n g t h , c o n t a i n i n g v a r y i n g s u l f a t e con c e n t r a t i o n s b e t w e e n 0.002 and 0.1 M. In a l l instances, duplicate e x p e r i m e n t s w e r e r u n w i t h good agreement b e t w e e n t h e s e t s . Mass b a l a n c e ( t h a t i s , p l u t o n i u m accounted f o r i n each v i a l ) g e n e r a l l y was g r e a t e r t h a n 9 5 % . 8
7
2
3
R e s u l t s and D i s c u s s i o n S t a b i l i t y c o n s t a n t s i n e a c h s y s t e m w e r e d e t e r m i n e d b y measu r i n g t h e d i s t r i b u t i o n c o e f f i c i e n t a s a f u n c t i o n o f HSO4 c o n c e n -
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
PLUTONIUM CHEMISTRY
tration. M a t h e m a t i c a l t r e a t m e n t o f t h e d a t a i s b a s e d on t h e method o f S c h u b e r t ( 8 ) , w h i c h h a s b e e n d e s c r i b e d many t i m e s p r e viously. I n e a c h s y s t e m , d a t a w e r e r e p r e s e n t e d a d e q u a t e l y by c o n s i d e r i n g t h e f o r m a t i o n o f o n l y a 1:1 and 1:2 c o m p l e x . The e x p r e s s i o n used t o f i t t h e d a t a i s g i v e n i n e q u a t i o n 2.
1/D = 1/D
[HSO~] J L + 3 /D
+ 3 /D
9
[HSOJ - V
2
(2)
ο 1 ο — ψ 2 ο [H+]m D a t a r e d u c t i o n was a c c o m p l i s h e d v i a n o n - l i n e a r r e g r e s s i o n formulae. C o e f f i c i e n t s o f t h e r e g r e s s i o n a n a l y s i s a r e AQ = 1/Do, AI = 3 i / ( D [ H + ] ) , and A = 3 /(Do [ ^ ] ) ; where η = m = 0, i f n
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o
m
0
2
2
P u C H S O i J x ^ " ^ " complexes a r e formed; η = 1 f o r PuSo£ ; m = 1 f o r 2
4
+
PuSO^HSO^; * m 2 f o r Pu(S0i ) . The v a l u e s f o r η and m a r e determined e x p e r i m e n t a l l y by r e p e t i t i o n o f c o m p l e x a t i o n e x p e r i ments a s a f u n c t i o n o f a c i d i t y . The v a l u e o f K i s d e t e r m i n e d a s the r a t i o o f A / A i , w i t h a p p r o p r i a t e c o r r e c t i o n f o r a c i d i t y (K = ( A [ t f ] ) / ( A [ H ] ) ) . A sample o f t h e d a t a f o r t h e P u ( I I I ) HSOi; a n d P u ( I V ) - H S 0 i ; s y s t e m s i s g i v e n i n T a b l e I . a n c
=
+
2
2
2
f
2
m
+
2
n
1
The P u ( I I I ) - H S O n S y s t e m . D a t a r e d u c t i o n i n t h e P u ( I I I ) - H S 0 Ç system i s c o m p l i c a t e d by t h e p o s s i b i l i t y t h a t s u l f a t e complexes o f P u ( I I I ) c o u l d be adsorbed by t h e r e s i n . Because t h e mathematical t r e a t m e n t i n t h e c a s e o f f o r m a t i o n o f a 1:1 c o m p l e x i s s i m p l e r , and a n y a d s o r p t i o n o f t h e 1:2 c o m p l e x i s l i k e l y t o be l e s s t h a n t h a t f o r t h e 1:1 c o m p l e x , e q u a t i o n s a p p l y i n g t o t h e l i m i t [HSOif] -> 0 ( i . e . , p r e d o m i n a n t l y 1:1 c o m p l e x i n s o l u t i o n ) w e r e d e r i v e d and a p p l i e d t o t h e a p p r o p r i a t e d a t a t o e v a l u a t e t h e p o s s i b i l i t y o f a d s o r p t i o n o f t h e 1:1 c o m p l e x . A s s u m i n g t h e 1:1 c o m p l e x i s PuSOt, t h e d i s t r i b u t i o n c o e f f i c i e n t i n t h e l i m i t o f l o w [HSOi;] i s : 3 +
[Pu ]
[PuS0^] ^ [PuS0p
+
D = [Pu
J +
]
+
a
r
(3) a
where t h e r s u b s c r i p t denotes s p e c i e s i n t h e r e s i n phase, and t h e a s u b s c r i p t d e n o t e s aqueous s p e c i e s . I f we d e f i n e A = [ P u S 0 t ] / [ p 0 t ] , and r
u S
a
+
[PuSO^][H ]
-
n
1
(4)
4
3 +
[Pu ] [HS0 ] a
4
e q u a t i o n 3 c a n be r e w r i t t e n : 3 +
+
[Pu ] D =
3 +
+ (AfL / [ H ] ) [ P u ] [HSO. ] i _ [Pu ] ( 1 + (fi / [ H ] ) [ H S 0 ] ) 3
J +
4
+
4
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
(5)
17.
NASH AND CLEVELAND
Table I
Sample d a t a f o r s t a b i l i t y c o n s t a n t
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P u ( I V ) -HSOç [HSOç] 0.0 .002 .004 .006 .008 .010 .015 .020 .025 .030 .035 .040 .045 .050 .055 .060 .065 .070 .075 .080 .085 .091 .096 .100
P u ( I I I ) -HSOI; 1/D
0.0508 .0784 .1046 .1570 .2004 .2490 .3857 .5949 .8776 1.012 1.186 1.594 2.004 2.544 3.196 3.823 4.276 4.616 4.926 5.612 6.309 7.337 7.695 7.719
= 0.050 M HClOi* = 1.00 M Τ = 25.0°C I = 2.00 M ΗΤΤΑ
255
Stability Constants
[HSOc] 0.0 .045 .091 .136 .182 .227 .273 .318 .364 .409 .454 .500 .545 .591 .636 .682 .727 .773 .818 .864
1/D 0.0608 .0706 .0820 .0915 .1000 .1080 .1224 .1294 .1420 .1698 .1832 .1869 .2050 .2160 .2331 .2344 .2484 .2694 .2769 .3179
HC10I+ = 1.00 M I = 2.00 M T = 25.0°C
determination P u ( I I I ) -HSOÇ [HSOc] 0.0 .045 .091 .136 .182 .227 .273 .318 .364 .409 .454 .500 .545 .591 .636 .682 .727 .773 .818 .864 .909
1/D 0.0681 .0758 .0824 .0867 .0977 .1034 .1110 .1196 .1304 .1379 .1500 .1514 .1668 .1860 .1929 .1935 .2014 .2067 .2344 .2389 .2500
HClOi* = 2.00 M I = 2.00 M T = 25.0°C
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
256
PLUTONIUM CHEMISTRY
3 +
3 +
D e f i n e D = [ P u ] / [ P u ] and C = A/D , and i n v e r t t o g e t e q u a t i o n 6: Q
r
a
0
1 + V
D
1 +
separate the v a r i a b l e s ,
(β,/lH+DtHSO"] ± ^ V (C3 /[H ])[HS0 ]
(6)
+
1
4
S u b t r a c t i n g 1 from both s i d e s o f equation 6 y i e l d s : +
(3-1 / [ H ] ) [HS0"7] -
(D /D - 1) = n
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1 +
(CÉW[H ])[HSO~] +
2 _ (C3 /[H ])[HS0 ]
it-
( ) 7
+
1
4
R e m o v a l o f [HSOîJ] t o t h e l e f t s i d e o f e q u a t i o n 7 and i n v e r s i o n r e s u l t s i n an e q u a t i o n h a v i n g t h e g e n e r a l form o f a s t r a i g h t l i n e :
[HSO-]/(D /D - 1) =
+ £
o
The
c o e f f i c i e n t s c a n be d e t e r m i n e d
vs.
[HSOI;] .
fHSO^]
(8)
by a p l o t o f [ H S O i l / ( D / D Q
- 1)
A p p l i c a t i o n o f e q u a t i o n 10 t o t h e e x p e r i m e n t a l D v s . [HSOTJ] d a t a d e t e r m i n e d a t 25°C and b o t h 1 and 2 M a c i d i t y y i e l d e d s t r a i g h t l i n e p l o t s w i t h s l o p e s i n d i s t i n g u i s h a b l e f r o m z e r o and reproduced t h e 3 i v a l u e s determined i n a n o n - l i n e a r r e g r e s s i o n f i t of the data. T h i s r e s u l t i m p l i e s no a d s o r p t i o n o f PuSO* by t h e r e s i n and j u s t i f i e s u s e o f t h e s i m p l e r d a t a t r e a t m e n t r e p r e s e n t e d b y e q u a t i o n 2. A s i m i l a r a n a l y s i s o f t h e T h ( I V ) - H S 0 5 s y s t e m done by Z i e l e n ( 9 ) l i k e w i s e p r o d u c e d r e s u l t s c o n s i s t e n t w i t h no a d s o r p t i o n o f T h S 0 £ by Dowex AG50X12 r e s i n . S t a b i l i t y c o n s t a n t s a s a f u n c t i o n o f t e m p e r a t u r e and t h e c a l c u l a t e d c o m p l e x a t i o n e n t h a l p i e s and e n t r o p i e s o f t h e a s s o c i a t e d r e a c t i o n s a r e g i v e n i n T a b l e I I . The r e s u l t s o f d u p l i c a t e e x p e r i ments a t 2.0 M a c i d i t y a n d i o n i c s t r e n g t h a r e shown a s t h e l a s t entry i n the table. C o m p a r i s o n o f t h e r e s u l t s a t 25°C, and 1.0 and 2.0 M a c i d i t y i n d i c a t e a n a p p r o x i m a t e i n v e r s e f i r s t o r d e r s t o i c h i u m e t r y i n [HT*~] f o r t h e and a c i d independence f o r K 2 . The p o s t u l a t e d r e a c t i o n s i n t h i s medium a r e g i v e n i n e q u a t i o n s 9 and 1 0 . Pu + HSO, -> PuSO. + H (9) and +
+
PuSot 4
+
HSOT 4
+
PuSO,HSO, 4 4
(10)
D e C a r v a l h o and C h o p p i n ( 1 0 , 11) p r e v i o u s l y h a v e r e p o r t e d t h e s t a b i l i t y c o n s t a n t s , c o m p l e x a t i o n e n t h a l p i e s , and e n t r o p i e s f o r a s e r i e s o f t r i v a l e n t l a n t h a n i d e and a c t i n i d e s u l f a t e s . As t h e i r w o r k was c o n d u c t e d a pH 3, t h e d o m i n a n t s u l f a t e s p e c i e s was So£~ and t h e m e a s u r e d r e a c t i o n was a s i n e q u a t i o n 12. M
3 +
+
S0?~ 4
+
MSot 4
Carnall and Choppin; Plutonium Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
(11)
17.
NASH AND CLEVELAND
257
Stability Constants
Table I I Pu(III)-HSOÏ s t a b i l i t y c o n s t a n t s , e n t h a l p i e s , and e n t r o p i e s , f o r t h e r e a c t i o n s r e p r e s e n t e d by e q u a t i o n s 9 a n d 1 0 , ( I = 2.00 M; [ H C l O i J = 1.00 M) Temperature (degrees C e l s i u s )
K
Downloaded by EAST CAROLINA UNIV on March 13, 2016 | http://pubs.acs.org Publication Date: May 19, 1983 | doi: 10.1021/bk-1983-0216.ch017
2.7 10.0 16.5 25.0 25.0* *Η010
4
4.25 4.06 3.92 3.57 2.17
κ
l
(+ (+ (4(+ (+
0.92 0.80 0.67 0.36 0.41
0.33) 0.47) 0.54) 0.26) 0.26)
(+ (+ (+ (+ (+
2
0.10) 0.14) 0.14) 0.08) 0.12)
= 2.00 M.
AG ΔΗ ΔΞχ X
Χ
= -3.15 (+ 0.18) k j / m = -5.2 (+ 1.0) kJ/m = -6.8 (+ 1.4) J/m-°K
AG ΔΗ AS
2
2
2
= +2.53 (+ 0.62) k j / m = -28.1 (+ 6.4) k j / m = -102 (+ 34) J/m-°K
To compare t h e p r e s e n t r e s u l t s w i t h t h o s e o f D e C a r v a l h o and C h o p p i n , o u r r e s u l t s i n 1 M a c i d must be c o r r e c t e d f o r t h e h e a t and e n t r o p y o f HS0I[ i o n i z a t i o n . Z e b r o s k i e t a l . (12) determined K = 0.084, w h i l e Z i e l e n ( 9 ) g i v e s t h e h e a t o f i o n i z a t i o n a s A H = +23.2 k j / m . The c a l c u l a t e d e n t r o p y i s A S = +98 j/m-°K. The t h e r m o d y n a m i c p a r a m e t e r s f o r t h e r e a c t i o n a
a
a
Pu
3 +
+
S0? 4
+
•> P u S o t