Concise Physical Chemistry

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

104 EQUILIBRIUM

and the other producing 4 mol of ATP

2 Glyceraldehyde-3-phosphate+2 phosphate+4 ADP→2 lactate+4ATP+2H 2 O

Thesummedreactionis

Glucose+2 phosphate+2 ADP→2 lactate+2ATP+2H 2 O

for a net gain of 2 mol of ATP. The first of these two reactions is unfavorable from

the point of view of a positive
G◦= 2 .2kJmol−^1 but at the initial concentrations

chosen to be at or near physiological concentrations,

Q=

( 0. 14 )^2 ( 0. 019 )^2

5. 0 ( 1. 85 )^2

= 0. 0196

(

3. 61 × 10 −^4

)

≈ 4 × 10 −^7  1

This very small reaction quotient drives the metabolic conversion of ADP to ATP

which then powers other reactions within the biological system as a whole.

PROBLEMS AND EXAMPLES

Example 7.1 Solution Calorimetry

A half-liter solution calorimeter system consisted of the calorimeter itself, a tempera-

ture measuring circuit, an electrical heating circuit, and calorimeter fluid. The system

was prepared with a solution of magnesium ion at 0.001 M. The ionic strength was

brought to 0.25 M with KCl, a neutral electrolyte, and the pH was adjusted to 7.0.

When the heating circuit was activated at a current flow ofIamperes for a timet,

an amount of heat energyqp= 96 .5 J was delivered through a heating resistorR

(q=I^2 Rt) producing a temperature rise of
T= 0 .166 K.^2 What was the water

equivalent (calorimeter constant) of the calorimeter system?

Solution to Example 7.1 The water equivalent of a calorimeter is the heat capacity

of the entire system as if it were all water even though it consists of various parts made

of various materials and contains a solution of reactants and products different from

pure water. The water equivalent can be found by a straightforward heat capacity

calculation even though we know that the heat capacity of the system is the sum of

many parts. We calculate

Cp=

dqp

dT

qp


T

=

95. 6

0. 166

=576 J K−^1 = 0 .576 kJ K−^1

(^2) 1 amp volt sec=1JandEin volts=IR.