Stability Constants, Enthalpies, and Entropies of Plutonium(III) and

17 Stability Constants, Enthalpies, and Entropies of Plutonium(III) and Plutonium(IV) Sulfate Complexes K. L. NASH and J. M. CLEVELAND

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

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 .


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.


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 -


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


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


(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


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


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


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


(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


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

Stability Constants, Enthalpies, and Entropies of Plutonium(III) and

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