Physical Chemistry Third Edition

598 13 Chemical Reaction Mechanisms II: Catalysis and Miscellaneous Topics

0 1020304050607080

1.0

0.8

0.6

0.4

0.2

0.0

(a)

(b)



/

0

 0510 mV

(limiting exponential form)

 05100 mV

 051000 mV

x/Å

Outer

Helmholtz

plane

Inner

Helmholtz

plane

Solvated cation

Diffuse layer

Metal

Specifically absorbed anion

x^5 Solvent molecule

1 x 2

Figure 13.14 The Electrical Double Layer.(a) The structure of the double layer

(schematic). From Bard and Faulkner,op. cit., p. 8. (b) The electric potential in the diffuse

double layer. From Bard and Faulkner,op. cit., p. 505.

EXAMPLE13.7

Find the Debye length at 298.15 K for an aqueous solution of HCl with a molality of

0 .0200 mol kg−^1.

Solution

The permittivity of water at this temperature is 6. 954 × 10 −^10 C^2 N−^1 m−^2 and the density

of water is 997 kg m−^3.

κe

(

2 NAvρ 1 I

εkBT

) 1 / 2