Spontaneous reaction Aris Kaksis Riga Univ. docent Biochemistry

Āris Kaksis Riga Stradin’s University Medical Chemistry 2013.

Spontaneous reaction condition Gibs free energy change negative ΔG_reac<0

http://aris.gusc.lv/BioThermodynamics/thermReacSpontaneouseE.doc

Studies in „Medical chemistry”, „Biochemistry”. Studies of Gibs free energy change calculation conditions

ΔG_reac = ΔH_reac – T ·ΔS_reac

ΔH_reac Enthalpy	ΔS_reac Entropy	T Temperature	ΔG_reac Free energy	Spontaneous ability of reaction
Dispersed energy T·ΔS_reac>0 is bound in surrounding and is lost as used free energy ΔG_reac<0	ΔS_reac>0 Positive entropy increases entropy change is positive	decomposition reaction	AB =>A + B	Biochemical catabolism in living organisms consume the free energy in spontaneous reactions maintain organisms living.
1. Endothermic Positive ΔH_reac>0		low T ΔH_reac>\|-T·ΔS_reac\|	Positive ΔG_reac>0 ΔH_reac–T·ΔS_reac>0	unfavorable reaction at low temperature
1. Endothermic Positive ΔH_reac>0	Dispersed energy is forming greater measure of chaos ΔS_reac>0 Positive . Spontaneous catabolic reactions	high T ΔH_reac<\|-T·ΔS_reac\|	Negative ΔG^°_reac< 0 ΔH_reac–T·ΔS_reac< 0	spontaneous reaction at high temperature
2. Exothermic Negative ΔH_reac<0	consume free energy change ΔG_reac<0 for life mantanance of organisms 37º C in human as well as to supply the heat for organisms as reaction Exothermic ΔH_reac<0	low T high T	Negative ΔG_reac< 0 ΔH_reac–T·ΔS_reac> 0	spontaneous reaction at any temperature
Living cell proliferations and existing conditions for Life	ΔS_reac<0 Negative entropy decreases entropy change is negative	synthesis reaction	A + B =>AB	Biochemical anabolism energy accumulates and organize in compounds as synthesized the higher order as well decreases measure of chaos ΔS_reac<0 Negative
3. Endothermic Positive ΔH_reac>0	Synthesized as well as produced free energy ΔG_reac>0 Positive accumulates in photosynthesis, in ATP synthesis, in polypeptides as well as in proteins,	any T	Positive ΔG_reac>0 ΔH_reac–T·ΔS_reac>0	unfavorable reaction thermodynamically forbidden at any temperature
4. Exothermic Negative ΔH_reac<0	in synthesized molecules, living cells live and proliferates	high T \|ΔH_reac\|<\|-T·ΔS_reac	Positive ΔG_reac>0 ΔH_reac–T·ΔS_reac>0	unfavoable rreaction at high temperature
4. Exothermic Negative ΔH_reac<0		low T \|ΔH_reac\|>\|-T·ΔS_reac\|	Negative ΔG_reac<0 ΔH_reac–T·ΔS_reac<0	spontaneous reaction at low temperature

In life important are negative change ΔS_reac<0 of entropy and positive increase ΔG_reac>0 of free energy!

Negative change ΔS_reac<0 dispersed energy TΔS decreases and into reaction accumulates supplied +Q energy into compound macroergic bonds as increase the free energy ΔG_reac>0.

ΔH_reac=ΔG_reac+T·ΔS_reac .

Opposite to spontaneous reaction ΔG_reac>0 negative change of free energy is lost energy.

Biochemical Reaction examples studies for students:

1. Glucose and oxygen Green plants Photosynthesis

red and blue light photons energy E=hν absorbtion

heat accumulates in glucose substance

ΔH_reac>0 EndothermicΔH_reac=+2863.82 kJ/mol

6CO₂ +6 H₂O + Q=2863.82 kJ/mol

photosynthetic proces ΔG_reac>0 is Endoergic ΔG_reac= +2840 kJ/mol

free energy accumulates in 1 mol cytosolic glucose molecules C₆H₁₂O₆ biochemically „combusted” by oxygen O₂ in mitochondria to combustion products CO₂ and H₂O along oxidative phosphorilation pathway and glycolise.

direct reaction

———————→

hoto

reverse reaction

←———————

oxygen

C₆H₁₂O₆+ 6 O₂

Glucose

biochemical

„combustion”

Glycolysis, Oxidative Phosphorylation

2. ATPase driven ATP synthesis (ATP adenosine tr

One mole of glucose C₆H₁₂O₆ produces glycolytical, mitochondrial totally 36 ATP molecules. Membrane integral enzyme ATPase nano engine to accumulate free energy ΔG_reac=+30.5 kJ/mol per produced ATP molecule under proton gradient drives in to reaction