Thermodynamic investigation of thiourea in water solutions

A C T A

U N I V E R S I T A T I S

L O D Z I E N S I S

FOLIA CHIMICA

1, 1982

S t e f a n i a T a n ie w s k a -O s iń s k a , B a r t ł o m i e j P a łe c z

THERMODYNAMIC INVESTIGATION OF THIOUREA IN WATER SOLUTIONS*

R e l a t i v e p a r t i a l

m o la l e n t h a l p i e s o f t h i o u r e a a n d w a te r

a n d e x c e s s

o f r e l a t i v e p a r t i a l

m o la l e n t r o p y o f w a te r w ere

d e te r m in e d fro m

e n t h a l p i e s o f s o l u t i o n

o f t h i o u r e a i n

wa­

t e r w i t h i n t h e te m p e r a t u r e r a n g e

2 9 3 . 15- 3 3 3 .1 5 K.

I n t r o d u c t i o n

i

-L-... .

* 1

The aim o f t h i s w ork was t o i n v e s t i g a t e th e a q u e o u s

s o l u t i o n s

o f t h i o u r e a fro m t h e th erm odyn am ic

p o i n t o f v ie w .

E n t h a l p i e s

o f

s o l u t i o n an d d i l u t i o n

o f t h i o u r e a (TU)

i n w a te r [ 1 ]

w ere d e t e r ­

m ined w i t h i n

t h e te m p e r a tu r e r a n g e

2 9 3 .1 5 - 3 3 3 .1 5 K.

R e s u l t s an d d i s c u s s i o n

On t h e b a s i s

o f t h e o b t a i n e d

i n t e g r a l e n t h a l p i e s

o f

d i l u t ­

i o n

(A H )

[ 1 ]

r e l a t i v e p a r t i a l m o la l

e n t h a l p i e s

o f t h e

s o l ­

v e n t

(L .,)

an d o f t h e

s o l u t e

(L g )

w ere c a l c u l a t e d i n T a b le 1 .

R e l a t i o n

L1 - f ( T ) ,

d e s c r i b e d

by a t h i r d - d e g r e e p o ly n o m ia l,

e n a b l e s u s t o

c a l c u l a t e t h e

a c t i v i t y o f

w a te r by m eans o f G ib b s

an d H e lm h o ltz

[ 2 , 3 ]

f o r m u la :

* T h e p r e s e n t w ork

h a s b ee n c a r r i e d o u t

an d s u p p o r t e d w i t h i n

t h e fram ew o rk o f

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I n t e r d e p a r t m e n t P ro b le m M R -I-1 1 .

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U s in g t h e v a l u e s o f ogmo-tic

c o e f f i c i e n t s o f t h i o u r e a i n

s o l u t i o n s

a t t h e te m p . 2 9 8 .1 5 K

o b t a i n e d by B on ner

e t »1

t h e e x c e s s

o f r e l a t i v e p a r t i a l m o la l

e n t r o p y o f

s o l v e n t

was c a l c u l a t e d

( T a b le 2 ,

F i g . 1)

o v e r t h e

te m p e r a t u r e

2 9 3 .1 5 - 3 3 3 .1 5 K.

T a b l e

E x c e s s o f r e l a t i v e p a r t i a l m o la l e n t r o p i e s

o f w a te r

f o r a q u e o n s t h i o u r e a a n d u r e a

s o l u t i o n s a t te m p e r a tu r e 2 9 8 .1 5 K

m

I-( m ole/kg)

AS^

(j/ra o le deg)

t h i o u r e a

u r e a

0 .1

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0 . 2

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1 .0

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1 .4

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1 .5

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i . e

0 .0 7 0 4 8

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w a te r

[ 4 ] ,

(AS®)

r a n g e

303.15 K(30°C)

313.15K |40°C)

323.15 K(50°Cl

333.15 K(60°C)

298,15 k (25°C)

1,0

, . .1

kg

. 1 . E x c e s s o f r e l a t i v e

p a r t i a l m o la l e n t r o p y

o f s o l v e n t AS1

a s a f u n c t i o n o f c o n c e n t r a t i o n o f t h i o u r e a i n w a te r

The v a l u e s o f

AS^

c a l c u l a t e d by u s

f o r t h i o u r e a

s o l u t i o n s

i n t e m p e r a t u r e

r a n g e u n d e r i n v e s t i g a t i o n

show t h e

s t r u c t u r e -

- b r e a k l n g c h a r a c t e r

o f t h i o u r e a .

The o b t a i n e d v a l u e s

o f

e x c e s s

o f r e l a t i v e p a r t i a l m o la l

e n t r o p y o f w a te r

a t t h e

te m p e r a t u r e

2 9 8 .1 5 K

a r e m ore p o s i t i v e

t h a n t h e v a l u e s

o f t h i s f u n c t i o n f o r

u r e a s o l u t i o n s [5 , 6 ]

( s e e T a b le 2 ) .

I t s u g g e s t s m ore

d e s t r u c ­

t i v e e f f e c t

o f t h i o u r e a m o le c u le s

on w a te r s t r u c t u r e

th a n

t h a t

o f u r e a m o l e c u le s .

On t h e b a s i s

o f h e a t c a p a c i t y a n d

s m a ll c h a n g e s i n t h e w a te r

p r o t o n s i g n a l ,

S u b ra m a n ia n

e t a l [ 7 ] r e a c h e d t h e

same

c o n l u -

s i o n a b o u t t h e

d e s t r u c t i v e e f f e c t

o f u r e a a n d

t h i o u r e a

on

t h e

s t r u c t u r e w a t e r ,

t h e e f f e c t o f t h i o u r e a b e in g

s t r o n g e r .

The more d e s t r u c t i v e

e f f e c t o f t h i o u r e a

on s p e c i f i c

w a te r

s t r u c t u r e i s

c a u s e d by

t h e r e p la c e m e n t o f

o x y g en atom i n a u r e a

m o le c u le by

a s u l p h u r atom [ a ; 9 ]

w h ich h a s

w e a k e r p r o t o n

a c ­

c e p t i n g a b i l i t y .

A p l a n a r t h i o u r e a

m o le c u le b e i n g

b i g g e r

t h a n

t h a t o f u r e a ,

d o e s n o t h a v e

enough room

i n t h e h y d ro g e n

bond

l a t t i o e o f w a t e r

s t r u c t u r e [ 1 0 ] .

REFERENCES

[1 ]

T a n i e w s k a - 0 t i ii a k a

S. ,

P a ł e c z

B . ,

J .

Chem. T herm odynam ics

1 2 , 775 (1 9 8 0 ),

[ 2 ]

I z m a i l o v

N. A .,

E le k t r o k h i m i a r a s t v o r o v ,

p .

1 1 2 .

I z d . K h a rk . U n iv . K harkov ( 1 9 5 9 ) .

[ 3 ]

R o b i n s o n

R. A. ,

S t o k e s

R . M .,

E l e c t r o l y t e s

S o l u t i o n s ,

London ( 1 9 5 5 ) .

[ 4 ]

B o n n e r

0 . D. t

J o r d a n

C. F . ,

A r i s m a n

R.

K. ,

B e d n a r e k

J . M .,

J . Chem. T herm o d y n am ics,

8 ,

1173 (1 9 7 6 )«

[ 5 ] Ł o g w i n i e n k o

R . ,

D o c to r a l t h e s i s »

Lódź U n i v e r s i ­

t y 1 9 7 2 .

[ 6 ]

B a r o n e

G. ,

E l i a

V. ,

R i z z o

E . ,

IV I n t e r n .

C o n f, C a l o r i m e t r y

an d T h erm o d y n am ics,

M o n t p e l l i e r ,

F ra n c e

( 1 9 7 5 ) .

[ 7 ]

S u b r a m a n i a n

S . ,

S a r m a

T. S. ,

B a l a s u-

b r a m a n i a n

D. ,

A h l u w a i i a

J . C . , J , P h y s .

C h em .,

7 5 , 815 (1 9 7 1 ) .

[ 8 ]

S t e w a r t

J . E . ,

J . Chem. P h y s .,

2 6 , 248 (1 9 5 7 ) .

[ 9 ]

P e^n k a l a

T . ,

Z a ry s k r y s t a l o c h e m l i ,

t . 2 ,

W arszawa

•

( 1 9 6 8 ) ,

s . 1 4 5 .

[ 1 0 ] S t ę p i e ń

A .,- U n i v e r s i t y o f L o d ź.

P e r s o n a l com m unica­

t i o n .

.

D e p a rtm e n t o f P h y s i c a l C h e m is try

\

I n s t i t u t e o f C h e m is try

U n i v e r s i t y o f

S t e f a n i a T a n le w s k a -O s iń s k a , B a r t ł o m i e j P a ł e c z

BADANIA TERMODYNAMICZNE ROZTWORÓW TIOMOCZNIK-WODA

Na p o d s ta w ie pom iarów

c a łk o w ite g o c i e p ł a

r o z p u s z c z a n i a

t i o ­

m o c z n ik a w w o d z ie [ 1 ] w p r z e d z i a l e t e m p e r a t u r

2 9 3 ,1 5 - 3 3 3 .1 5 Kwy­

l i c z o n o w a r t o ś c i

w z g lę d n y ch c z ą s tk o w y o h

molowych e n t a l p i i

wody

( L ,)

i tio m o c z n ik a

( L ? ) .

K o r z y s t a j ą c z w a r t o ś c i

( L j)

o r a z a k ­

ty w n o ś c i wody

w t y c h m ie s z a n in a c h

w yznaczono n a d m ia r

w z g lę d n e j

c z ą s t k o w e j m olow ej e n t r o p i i

r o z p u s z c z a l n i k a

(A Sj1) .

P rz e p ro w a ­

d z o n a a n a l i z a

w spom nianych f u n k c j i

term o d y n a m ic z n y c h

w z a l e ż n o ­

ś c i od s t ę ż e n i a

1 te m p e r a tu r y

w s k a z u je n a

s i l n i e j

n i s z c z ą c y

wpływ tio m o c z n ik a n i ż m o czn ik a n a

s t r u k t u r ę w ody.

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