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Posted by on Saturday, April 28, 2012 at 2:28pm.

I can't seem to get this problem, i really don't understand it
Chemical reactions can also be coupled. The decreasing free energy of a spontaneous change can be stored in substance whose formation would not ordinarily be spontaneous. Living organisms have a remarkable ability to couple reactions in order to make the most of the free energy that passes through. The principle biological free- energy reservoir is the ATP-ADP system. When adenosine diphosphate (ADP) molecules add phosphate units to produce adenosine triphosphate( ATP) molecules, they store 31 kj/mol of free energy that can be release when the reaction is reversed :
ADP^(3-)(aq)+ HPO4^(2-)(aq)+H^(+) „³ ATP^(4-)(aq) +H2O(l) delta G =31kJ
In a living cell, this free energy is supplied by the oxidation of glucose to CO2 and H2O:
C6H12O6(s)+6O2(g)„³6CO2(g)+6H2O(l) delta G = -2870kJ
The oxidationof 1 mol of glucose releses 2870 kJ of free energy. Some of this energy is used to convert 36 mol of ADP to ATP:
36ADP^3-(aq) + 36HPO4^2-(aq) +36H^+(aq) -->36ATP^4(aq)- + 36H2O(l) delta G = (36)(31)= 1100kJ
Hence, 1100kJ, or 38%, of the energy released by 1 mol of glucose is stored in ATP. The ATP later releases this energy as needed. Some of the energy is used for muscle action, and some is used to synthesize highly organized biomolecules and structural elements. In this way, living organisms are able to exist as temporary islands of low entropy in an increasingly disordered environment. Eventually, the stored energy is released, and the universe obtains its full entropy increase.
1)Calculate the equilibrium constant at 25 degrees Celsius for the hydrolosis of adenosine triphosphate (ATP) into adenosine diphosphate (ADP):
ATP^(4-)+ H2O(l)<-„³ADP^(3-)(aq)+HPO4^(2-)(aq)+H^(+)(aq)

2)In human red blood cells, the concentrations of ATP^(4-), ADP^(3-) and HPO4^(2-) are 2.25 mM, 0.25mM and 1.65 mM respectively. Estimate delta G and use it to show which reaction, forward or reverse, is capable of providing useful work.
Assume that the pH is 7 and the temperature is 25 degrees Celsius .

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