Chapter 17 - Entropy, Free Energy, and Equilibrium
The first of thermodynamics' three laws, according to which energy can be transferred from one form to another but not created or destroyed.
The amount of heat given out or absorbed by a system during a constant-pressure operation, which chemists characterize as a change in enthalpy (H), is one measure of these changes.
The 2nd thermodynamics law explains why chemical processes tend to be one-way.
The third legislation is an extension of the second legislation
The term "spontaneous reaction" refers to a reaction that occurs in a given set of circumstances.
If we assume that the system's energy is reduced by spontaneous processes, we can explain why a ball is rolling downhill and why it springs in a clock.
Likewise, there are many spontaneous exothermic reactions.
The assumption in this case is that spontaneous processes are always reducing the energy of a system.
Experience tells us that, though the process is endothermic, ice melts spontaneously over 0° C.
The dissolution of ammonium nitrate in water is a further example against our supposition.
We need to create a new thermodynamic variable called entropy to anticipate the spontaneity of a process.
Entropy (S) is a measure of how to spread out or dispersed a system's energy is among the numerous alternative ways that a system can contain energy.
Distribution III is most likely because it is achieved by 6 microstate or 6 different modes.
Distribution I is least likely because it has one microstate.
On the basis of this analysis, the likelihood of a particular distribution (state) occurring is determined by the number of ways in which the distribution is achieved (microstates).
As the number of molecules approaches the macroscopic scale, it is not hard to see that they are distributed evenly between the two compartments, as there are many, many more microstats in this distribution than any other distribution.
The second law of thermodynamics expresses the relationship between entropy and reaction spontaneity:
In a spontaneous process, the entropy of the cosmos grows, while in an equilibrium process, it remains unchanged.
The difference in standard entropies between products and reactants determines the standard entropy of reaction Srxn °, just as it does for the enthalpy of a reaction.
The entropy of a perfect crystalline solid is zero at absolute zero temperature, according to the third rule of thermodynamics.
Since gasses are invariably more entropic than liquids and solids.
Predicting the sign of −S° is harder for reactions involving only liquid and solids;
however in many such cases an increase of the total number of molecules and/or ions accompanies an increase in entropy
The free-energy change for a reaction when it occurs under standard-state conditions when reactants in their standard states are transformed to products in their standard states, is known as the standard free-energy of reaction (G°rxn).
ΔG < 0 The reaction is spontaneous in the forward direction.
ΔG > 0 The reaction is nonspontaneous.
The reaction is spontaneous in the opposite direction.
ΔG = 0 The system is at equilibrium.
There is no net change
Case 1: A significant negative value of G° will cause G to be negative as well.
As a result, unless a considerable amount of product has been generated.
the net reaction will proceed from left to right.
Case 2: A large positive G° term tends to make G positive as well.
As a result, unless a considerable amount of reactant has been created, the net reaction will proceed from right to left.
Even though many biological reactions have a positive G° value, they are necessary for life to exist.
These reactions are related to an energetically advantageous process in biological systems, one with a negative G° value.
Enzymes make a wide range of non-spontaneous reactions easier in biological systems.
For instance, during metabolism in the human body, glucose-related food molecules.
(C6h12O6) are converted into dioxide and water with a significant free energy release: C6H12O6(s) + 6O2(g) ⟶ 6CO2(g) + 6H2O(l) ΔG° = −2880 kJ/mol
Free energy is stored until cells are needed by ATP.
ATP is hydrolysed for ADP and phosphoric acid under appropriate circumstances, with 31 kJ/mol free energy releases, which can be used to power unfavorable reactions such as protein synthesis.
The first of thermodynamics' three laws, according to which energy can be transferred from one form to another but not created or destroyed.
The amount of heat given out or absorbed by a system during a constant-pressure operation, which chemists characterize as a change in enthalpy (H), is one measure of these changes.
The 2nd thermodynamics law explains why chemical processes tend to be one-way.
The third legislation is an extension of the second legislation
The term "spontaneous reaction" refers to a reaction that occurs in a given set of circumstances.
If we assume that the system's energy is reduced by spontaneous processes, we can explain why a ball is rolling downhill and why it springs in a clock.
Likewise, there are many spontaneous exothermic reactions.
The assumption in this case is that spontaneous processes are always reducing the energy of a system.
Experience tells us that, though the process is endothermic, ice melts spontaneously over 0° C.
The dissolution of ammonium nitrate in water is a further example against our supposition.
We need to create a new thermodynamic variable called entropy to anticipate the spontaneity of a process.
Entropy (S) is a measure of how to spread out or dispersed a system's energy is among the numerous alternative ways that a system can contain energy.
Distribution III is most likely because it is achieved by 6 microstate or 6 different modes.
Distribution I is least likely because it has one microstate.
On the basis of this analysis, the likelihood of a particular distribution (state) occurring is determined by the number of ways in which the distribution is achieved (microstates).
As the number of molecules approaches the macroscopic scale, it is not hard to see that they are distributed evenly between the two compartments, as there are many, many more microstats in this distribution than any other distribution.
The second law of thermodynamics expresses the relationship between entropy and reaction spontaneity:
In a spontaneous process, the entropy of the cosmos grows, while in an equilibrium process, it remains unchanged.
The difference in standard entropies between products and reactants determines the standard entropy of reaction Srxn °, just as it does for the enthalpy of a reaction.
The entropy of a perfect crystalline solid is zero at absolute zero temperature, according to the third rule of thermodynamics.
Since gasses are invariably more entropic than liquids and solids.
Predicting the sign of −S° is harder for reactions involving only liquid and solids;
however in many such cases an increase of the total number of molecules and/or ions accompanies an increase in entropy
The free-energy change for a reaction when it occurs under standard-state conditions when reactants in their standard states are transformed to products in their standard states, is known as the standard free-energy of reaction (G°rxn).
ΔG < 0 The reaction is spontaneous in the forward direction.
ΔG > 0 The reaction is nonspontaneous.
The reaction is spontaneous in the opposite direction.
ΔG = 0 The system is at equilibrium.
There is no net change
Case 1: A significant negative value of G° will cause G to be negative as well.
As a result, unless a considerable amount of product has been generated.
the net reaction will proceed from left to right.
Case 2: A large positive G° term tends to make G positive as well.
As a result, unless a considerable amount of reactant has been created, the net reaction will proceed from right to left.
Even though many biological reactions have a positive G° value, they are necessary for life to exist.
These reactions are related to an energetically advantageous process in biological systems, one with a negative G° value.
Enzymes make a wide range of non-spontaneous reactions easier in biological systems.
For instance, during metabolism in the human body, glucose-related food molecules.
(C6h12O6) are converted into dioxide and water with a significant free energy release: C6H12O6(s) + 6O2(g) ⟶ 6CO2(g) + 6H2O(l) ΔG° = −2880 kJ/mol
Free energy is stored until cells are needed by ATP.
ATP is hydrolysed for ADP and phosphoric acid under appropriate circumstances, with 31 kJ/mol free energy releases, which can be used to power unfavorable reactions such as protein synthesis.
