Concise Physical Chemistry

c07 JWBS043-Rogers September 13, 2010 11:25 Printer Name: Yet to Come

PROBLEMS AND EXAMPLES 105

Example 7.2 Adenosine 5′-triphosphate ATP

The hydrolysis of adenosine 5′-triphosphate ATP to adenosine 5′-diphosphate ADP

plus an inorganic phosphate ion can be written

AT P+H 2 O→ADP+phosphate

If 10 mL of ATP with concentration[AT P]= 0 .200 mol L−^1 are pipetted into a

calorimeter with a heat capacity of 0.576 kJ K−^1 (Example 7.1) and a temperature rise

of 0.107 K is found, what is the enthalpy of hydrolysis of adenosine 5′-triphosphate

to adenosine 5′-diphosphate plus an inorganic phosphate ion under these conditions?

What is the sign of
rH?

Solution to Example 7.2

0 .107 K

(

0 .576 kJ K−^1

)

= 0 .0616 kJ

10 .0mL= 0 .0100 L

0 .0100 L(0.200 mol L−^1 )= 0 .00200 mol ATP

0 .0616 kJ

0 .00200 mol

=− 30 .8kJmol−^1

The sign of
rHis negative because the reaction is exothermic. Heat flowing out

of the reacting system at constant external pressure means that its enthalpy balance

must decrease.

Problem 7.1

What is the change in the entropySfor one mole of a pure substance for an infinites-

imal change inTandp? Given: Entropy is an exact differential

dS(T,p)=

(

∂S

∂T

)

p

dT+

(

∂S

∂p

)

T

dp

Problem 7.2

In an experiment on the nitrogen tetroxide reaction at 298 K

N 2 O 4 (g) →← 2NO 2 (g)

pure N 2 O 4 (g) was introduced into a reaction vessel maintained at constant temperature

and a total pressure of 2.500 bar. When equilibrium had been reached, the partial