Cliffs AP Chemistry, 3rd Edition

(d) Restatement: Calculate Kat 500°C and 1 atm.

. RT T log

HT T

K

∆ K

2 303 T

T

12

21

1

%^h- = 2

(. )(. )( )( )

,

logKK

JK K K

JK K

2 303 8 314 773 298

57 200 773 298

(^1298)
773
:

• 
  


• =

`j

616. =logKK 298773

log K 773 −log K 298 = 6.16

log K 298 = − 0.838 from part (c)

log K 773 = 6.16 + (−0.838) = 5.32

K =2.09 ×l0^5

(e) Restatement: Calculate ∆S°at 298 K and 1 atm.

∆G°= ∆H°−T∆S°

,,

∆S ∆∆Η T G 298

57 200 4 780

K^176

JJ

= - = JK:^1

% =

% % -

(f) Restatement: Calculate the temperature at which ∆G°is equal to zero at 1 atm, assuming

that ∆H°and ∆S°do not change significantly as the temperature increases.

∆G°= ∆H°−T∆S°

0 = 57,200 J −T(176 J ⋅K–1)

,

T

176

57 200

325

JK

J

1 K

:

==-

2. (a) Define the concept of entropy.
   (b) From each of the pairs of substances listed, and assuming 1 mole of each substance,
   choose the one that would be expected to have the lower absolute entropy. Explain
   your choice in each case.
   (1) H 2 O(s) or SiC(s) at the same temperature and pressure
   (2) O 2 (g) at 3.0 atm or O 2 (g) at 1.0 atm, both at the same temperature
   (3) NH 3 (,) or C 6 H 6 (,) at the same temperature and pressure
   (4) Na(s) or SiO 2 (s)

Answer

2. (a) Restatement: Define entropy.
   Entropy, which has the symbol S, is a thermodynamic function that is a measure of
   the disorder of a system. Entropy, like enthalpy, is a state function. State functions
   are those quantities whose changed values are determined by their initial and final
   values. The quantity of entropy of a system depends on the temperature and pressure

of the system. The units of entropy are commonly J ⋅K–1⋅mole–1. If Shas a °(S°),

Energy and Spontaneity