Concise Physical Chemistry

c05 JWBS043-Rogers September 13, 2010 11:25 Printer Name: Yet to Come

82 ENTROPY AND THE SECOND LAW

Problem 5.3

What is the entropy of isothermal mixing of 1 mol of helium with 1 mol of argon if

the two gases start out in separate chambers, each at 1 bar pressure, and they produce

2 mol of mixed gases also at 1 bar pressure?

Problem 5.4

Industrial production of ammonia NH 3 is carried out by combination of the elements

at aboutT=650 K andp=400 bar (Metiu, 2006):

3H 2 +N 2 →2NH 3

What is the enthalpy change for this reaction at this temperature and pressure? For

simplicity, assume ideal behavior of all three gases.

Problem 5.5

What is the enthalpy change for the pressure change from 1.0 bar to 40 MPa?

Problem 5.6

Sulfur dioxide has a heat of fusion of 7.41 kJ mol−^1 at its melting point of 200 K.

Find the entropy change for the melting process

SO 2 (s)→SO 2 (l)

How does this compare with the entropy change for melting ice which has


Hfusion=333.6 J g−^1 (CRC Handbook of Chemistry and Physics, 2008–2009,

89th ed.)

Problem 5.7

On theoretical grounds, Peter Debye proposed what is known as the Debye third-

power law for the entropy of perfectly crystalline solids near absolute zero K.

Cp=AT^3 , T<15 K

Solid chlorine Cl 2 (s) has a heat capacity ofCp= 3 .72 J K−^1 mol−^1. What is the

entropy of Cl 2 (s) atT=15 K?