�BIO chemical Thermodynamics��By�Sumit Sharma�Deptt,. Of Biotechnology
BIOENERGETICS
THERMODYNAMICS
It is the branch of physical chemistry that deals with the energy changes.
Science of the relationship between heat, work, temperature, and energy.
Thermodynamics, deals with the transfer of energy from one place to another and from one form to another.
BIOENERGETICS
It is the field of biochemistry concerned with the transformation and use of energy by the living cell.
In biological system, the heat energy cannot be used to drive the vital processes obtain energy by chemical linkage to oxidation reactions.
The simplest type of coupling may be represented by the equation.
A + C B + D + Heat
The conversation of metabolite A to B occurs with the release of energy. It is coupled to another reaction, wherein energy is required to convert metabolite C to metabolite D.
CONCEPT OF ENERGY
Energy
It is defined as the capacity to do work , which is the product of a given force acting through a given distance
Work = force × displacement
It is one of the fundamental components of any system. Energy exist in variety of forms such as electrical, mechanical and chemical energy etc.
THERMODYNAMIC QUANTITIES
We define three thermodynamic quantities that describe the energy changes occurring in a chemical reaction.
These are the characteristic features of a system, capable of specifying the systems state.
GIBB’S FREE ENERGY (G)-
When a reaction proceeds with the release of free energy, the free energy change ΔG , has a negative value and the reaction proceeds spontaneously with the loss of free energy i.e., it is EXERGONIC. If in addition, ΔG is of great magnitude, the reaction goes virtually to completion and is essentially irreversible.
In endergonic reaction the system gains free energy and ΔG is positive and the reaction proceeds only if free energy can be gained i.e., it is ENDERGONIC. If in addition ΔG is of high magnitude, the system is stable with little or no tendency for a reaction
ENTHALPY (H)
Enthalpy is the heat content of the reacting system . It reflects the no. and kinds of chemical bonds in the reactants and products. When a chemical reaction releases heat , it is said to be exothermic; the heat contents of the products is less than that of the reactants and ΔH has , by convention , negative value. Reacting systems that take up heat from the surroundings are endothermic and has positive value of ΔH.
ENTROPY (S)
It is the quantitative expression for the randomness or disorder in the system. When the products of the reaction are less complex and more disordered then the reactants , the reactions is said to proceed with gain in entropy.
Relationship Between Thermodynamic Quantities
Under the condition existing in biological system , changes in free energy , enthalpy and entropy are related to each other quantitatively by the equation;
ΔG = ΔH – TΔS
Where,
ΔG = change in gibbs free energy of the reacting system
ΔH = change in enthalpy of the system T = absolute temperature
ΔS = change in entropy of the system
FIRST LAW OF THERMODYNAMICS
It is the principle of conservation of energy. It states that the total amount of energy in the universe (i.e., system and surroundings ) remains constant. Energy can neither be created nor destroyed during a given process.
It may undergo transformation from one form to another.
Example - Chemical energy can be transformed into mechanical, thermal, radiant or electrical energy.
SECOND LAW OF THERMODYNAMICS
The Second law of thermodynamics states that physical and chemical processes proceed in such a way that the randomness or disorder of the universe (the system and its surroundings) increase to the maximum possible.
IT CAN BE EXPLAINED WITH THE HELP OF FOLLOWING EXAMPLE
The expansion of gas into an empty cylinder simply redistributes the gas molecules until equilibrium is reached. The total no. of molecules remain unchanged .
COMBINING FIRST AND SECOND LAW
The entropy changes of chemical reaction are not readily measurable, the entropy is not used as a criterion whether a biochemical process can occur spontaneously or not.
For spontaneity, both the entropy changes should be known. These difficulties are alleviated by using a different thermodynamic function called free energy(G).
FREE ENERGY FUNCTION WAS CREATED BY COMBINING FIRST AND SECOND LAW OF THERMODYNAMICS IN THE FORM OF FOLLOWING EQUATION -
ΔG = ΔH – TΔS
Where,
ΔG = change in gibbs free energy of the
reacting system
ΔH = change in enthalpy of the system T = absolute temperature
ΔS = change in entropy of the system
References
Thank you !