Physical Chemistry , 1st ed.

2.56.1.20 g of benzoic acid, C 6 H 5 COOH, is burned in a
porcelain dish exposed to the air. If 31,723 J of energy is given
off and the system temperature is 24.6°C, calculate q, w, H,
and U. (Compare your answers to those from the previous
problem.)

2.11 Changing Temperatures

2.57.Assuming constant heat capacities for products and re-
actants, determine the H(500°C) for 2H 2 (g) + O 2 (g) →
2H 2 O (g). (Hint:be careful which data you use for water!)

2.58.Use the heat capacities of the products and reactants of
the thermite reaction and the calculated Hof the process to
estimate the temperature of the reaction. Assume that all of
the heat generated goes to increasing the temperature of the
system.

2.59.The following are values of heat capacity for nitrogen
gas:

Temp (K) CV(J/molK)

300 20.8

400 20.9

500 21.2

600 21.8

700 22.4

800 23.1

900 23.7

1000 24.3

1100 24.9

Using the general formula CVA+ BT+ C/T^2 , find values of
A, B, and Cthat fit the given data.

2.60.What is Ufor 1 mole of N 2 gas going from 300 K to

1100 K at constant volume? Use the expression for CVyou de-

termined from exercise 2.59, and evaluate Unumerically.

2.61.Consider a gas undergoing a reversible, adiabatic

change in volume. Such changes are not isothermal, but you

can still use the special case of Boyle’s law in equation 2.49.

Plot the final pressure of 1.00 mole of ideal gas at 1.00 bar ini-

tial pressure as the volume increases. Also plot the isothermal

final pressure as volume increases from the same initial condi-

tions (that is, Boyle’s law). How do these two plots compare?

Exercises for Chapter 2 65

Symbolic Math Exercises