Concise Physical Chemistry

c04 JWBS043-Rogers September 13, 2010 11:24 Printer Name: Yet to Come

70 THERMOCHEMISTRY

Problem 4.8

Plot the heat capacity of ethylene from the following data set:

Temperature (K) Heat capacity,Cp(J K−^1 mol−^1 )

300.0000 43.1000

400.0000 53.0000

500.0000 62.5000

600.0000 70.7000

700.0000 77.7000

800.0000 83.9000

900.0000 89.2000

1000.0000 93.9000

Problem 4.9

Suppose that the heat capacitiesCpfor N 2 ,H 2 , and NH 3 in the standard state are

constant with temperature change (they aren’t) at 29.1, 28.8, and 35.6 J K−^1 mol−^1.

Suppose further that
rH◦for the reaction

N 2 +3H 2 →2NH 3

is−92.2 kJ mol−^1 (of N 2 consumed) at 298 K. What is
Cpfor the reaction? What

is
rH◦at 398 K? What is the (hypothetical)
rH◦at 0 K?