First and Second law of thermodynamics. Concept of entropy, Free energy, and enthalpy.

1. Unit 1.0
Module 1.0
Prof. V. M. Chaudhari
Department of Microbiology,
PSGVPMandal’s ASC College,
Shahada.
T.Y.B.Sc. CBCS June 2020-2021
TYBSc. 2020-21 CBCS. Dr.VMC

2. Learning objectives
• Laws of thermodynamics
• First Law of Thermodynamics
• Second Law of Thermodynamics
• Concept of entropy
• Free energy
• Enthalpy
TYBSc. 2020-21 CBCS. Dr.VMC

3. First Law of
Thermodynamics
Second Law of
Thermodynamics
Entropy
Free
energy
Enthalpy
Bioenergetics
TYBSc. 2020-21 CBCS. Dr.VMC

4. Bioenergetics
Bioenergetics or biochemical thermodynamics
deals with the study of energy changes
accompanying the biochemical reactions.
The reactions are broadly classified as
Exothermic reaction (energy releasing) and
Endothermic reaction (energy consuming)
Bioenergetics is concerned with the initial and
final states of energy component of the reaction.
TYBSc. 2020-21 CBCS. Dr.VMC

5. All Biological energy transformations obey the laws of
thermodynamics.
The first law of thermodynamics also known as Law of
conservation of energy.
Based on the Principle of conservation of energy.
Statement 1.
Energy can be neither created nor destroyed.
Only energy transformed from one from to another.
Total amount of energy of the universe remains constant.
Laws of Thermodynamics
TYBSc. 2020-21 CBCS. Dr.VMC

6. Statement 2.
Energy in one form if disappears, it make its
appearance in an exactly equivalent quantity in
another form.
During burning of coal chemical energy yield heat which
moves engine to move train. Thus energy in one form
disappears it make its appearance in another form.
TYBSc. 2020-21 CBCS. Dr.VMC

7. Statement-
Second Laws defines entropy as a randomized state of
energy unavailable to do work.
Entropy of the universe increases during all
chemical and physical natural processes.
It means the natural tendency of any system is to become
more disordered results in increase in entropy.
Second law of thermodynamics
TYBSc. 2020-21 CBCS. Dr.VMC

8. Entropy is a quantitative expression for the randomness or
disorder in a system.
Second law introduces the concept of entropy.
It is amount of energy unavailable for conversion into work.
The term entropy was introduced by Clausius in 1865. It is
denoted by Symbol S.
Entropy is expressed in terms of entropy unit EU, which have
dimensions of Calories/mole/degree.
Entropy
TYBSc. 2020-21 CBCS. Dr.VMC

9. Significance
1. A characteristics of a spontaneous process is accompanied
by an increase in the disorder or randomness of the molecule
constituting the system.
2. A spontaneous process always proceed to attain a state of
equilibrium.
When the products of a reaction are less complex and more
disordered than the reactants, the reaction is said to proceed
with a gain in entropy.
TYBSc. 2020-21 CBCS. Dr.VMC

10. The amount of energy that can do work during a reaction at
constant temperature and pressure is called free energy.
In biological system free energy is the most important type of
energy. Free energy is denoted by symbol G given by J.
Gibbs.
Free energy is measure of the potential energy of the
substance it can not be measured directly but change in free
energy of a reaction can be measured.
It is denoted by symbol ΔG.
GIBBS FREE ENERGY, G
TYBSc. 2020-21 CBCS. Dr.VMC

11. The change in free energy ΔG, of a reaction is calculated by
taking the difference between the sum of free energies of the
products and that of reactants.
A + B ↔ C + D
ΔG = Free energy = G products – G reactants
ΔG = (GC+GD) – (GA+GB)
Unit of ΔG= Joules/mole(J/mol) or Calories/mole(cal/mol)
ΔG= negative(-) when reaction is exothermic
ΔG= positive (+) When reaction is endothermic
ΔG= zero(0) at the stage of equiibriumTYBSc. 2020-21 CBCS. Dr.VMC

12. Enthalpy, is the heat content of the reacting system.
It is denoted by symbol H.
It reflects the number and kinds of chemical bonds in the
reactants and products.
The enthalpy change ΔH is defined as the amount of heat the
reacting system releases to or absorb from the surrounding at
constant temperature and pressure.
Unit of ΔH= Joules/mole(J/mol) or Calories/mole(cal/mol)
Enthalpy
TYBSc. 2020-21 CBCS. Dr.VMC

13. ΔH= negative when a chemical reaction releases heat,
reaction is exothermic
ΔH= positive when reacting systems take up heat from
their surroundings and are endothermic.
TYBSc. 2020-21 CBCS. Dr.VMC

14. TYBSc. 2020-21 CBCS. Dr.VMC