Concise Physical Chemistry

c13 JWBS043-Rogers September 13, 2010 11:27 Printer Name: Yet to Come

PROBLEMS AND EXAMPLES 219

(c) Find the equilibrium constantKwfor the dissociation of pure water.

(d) Find the concentration of hydrogen ions H+in pure water.

(e) Why is it meaningful to calculate the equilibrium constant for H+even though

we know that H 3 O+,H 5 O+,...also exist in pure water?

Problem 13.8

The molar conductivities of NaCl are given in the handbook as

mol dm−^3 Conductivity mol dm−^3 Conductivity

5.0000e-4 124.4400 1.0000e-3 123.6800

5.0000e-3 120.5900 0.0100 118.4500

0.0200 115.7000 0.0500 111.0100

0.1000 106.6900

Plot these data in the form of a Kohlrausch plot. Determine the value of◦NaCland

the slope of the linear extrapolation to◦NaCl.

Problem 13.9

The molar conductivities◦of NH 4 Cl,NaOH,and NaCl are 149.6, 247.7, and

126.4 in units of 10^4 Sm^2 mol−^1 .Find◦NH 4 OH.

Problem 13.10

Show that the units of conductivityκare ohm−^1 m−^1.

Problem 13.11

One meaning of the term Gibbsfreeenergy is that
Gis the maximum work that

can be obtained from a chemical reaction. Conversely, the negative of
Gis the

minimum work that must be put into a chemical system to reverse its direction. Given

that
G=−237 kJ mol−^1 for the spontaneous reaction (note the sign of
G)

H 2 (g)+^12 O 2 (g)→H 2 O(l)

and the fact that workw=charge(V) where the charge is in coulombs and V is the

voltage, find the minimum potential in volts necessary for the electrolysis of water to

form H 2 (g)+^12 O 2 (g).