Concise Physical Chemistry

(Tina Meador) #1

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 positiveG◦= 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 ofT= 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.

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