Thermodynamics
A knowledge of thermodynamics enables one to determine whether a physical procedure is possible, and is needed for understanding why proteins fold to their native conformation, why some enzyme-catalyzed reactions needed an how muscles generate mechanical force, input of energy, etc. Thermodynamics is the explanation of the relationships between the several forms of energy and how energy affects matter on the macroscopic level. That is applies to biochemistry thermodynamics which is most frequent concerned with describing the conditions under that processes occur spontaneously through themselves.
In thermodynamics a system is the matter within a described region. The matter in the rest of the universe is known as the surroundings. First law of the thermodynamics a mathematical statement of the law of conservation of energy states in which the total energy of a system and its surroundings is a stable:
ΔE = EB - EA =Q-W
in that EA is the energy of the system at the begin of a procedure and EB at the end of the procedure. Q is the heat absorbed through the system and W is the work done through the system. The change in energy of a system depends only on the initial and ?nal states and not on how it reached that state. Processes in that the system releases heat example for have a negative Q are known as exothermic processes; those in that the system gains heat instance example have a positive Q are known as endothermic. The SI unit of energy is the J (Joule), although the cal (calorie) is still often used 1 kcal 4.184 kJ.
First law of the thermodynamics cannot be used to predict whether a reaction can occur spontaneously as some spontaneous reactions have a positive ΔE. Thus a function variant from ΔE is needed. One such function is S (entropy), that is a measure of the degree of randomness or disorder of a system. The entropy of a system raise ΔS is positive when the system becomes more disordered. The 2nd law of thermodynamics states in which a process can occur spontaneously only if the sum of the entropies of the system and its surroundings increases or in which the universe tends towards maximum disorder which is:
( ΔSsystem - ΔSsurroundings ) > 0 for a spontaneous process
Moreover, using entropy as a criterion of whether a biochemical procedure can occur spontaneously is hard, as the entropy changes of chemical reactions are not readily measured and the entropy change of both the system and its surroundings must be known. These dif?culties are overcome through using a various thermodynamic function, free energy (G), proposed through Josiah Willard Gibbs that merge the ?rst and second laws of thermodynamics:
ΔG =ΔH - TΔS
in that ΔG is the free energy of a system undergoing a transformation at constant P (pressure) and T (temperature), ΔH is the change in enthalpy (heat content) of this system and in that ΔG is the free energy of a system undergoing a transformation at constant P (pressure) and T (temperature), ΔH is the change in enthalpy (heat content) of this system and ΔS is the modify in the entropy of this system. The enthalpy change is given through: is the modify in the entropy of this system. The enthalpy change is given through:
ΔH = ΔE+ PΔV
The volume change (ΔV) is small for nearly all biochemical reactions, and so ΔH is nearly equivalent to ΔE. Thus
ΔG = ΔE -TΔS
Therefore, the ΔG of a reaction depends both on the change in internal energy and on the change in entropy of the system. The modification in free energy ΔG of a reaction is a valuable criterion of whether which reaction can occur spontaneously:
- Only if ΔG is negative a reaction can occur spontaneously;
- If ΔG is zero a system is at equilibrium;
- If ΔG is positive a reaction cannot occur spontaneously. An input of energy is needed to drive such a reaction;
- If a reaction the ΔG is independent of the path of the transformation;
- ΔG gives no information about the rate of a reaction.