The branch of science which deals with energy changes in physical and chemical processes is called thermodynamics



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The branch of science which deals with energy changes in physical and chemical processes is called thermodynamics

  • The branch of science which deals with energy changes in physical and chemical processes is called thermodynamics

  • Some common terms which are frequently used in the discussion of thermodynamics are:



System

  • System





System is a specified part of the universe which is under observation

  • System is a specified part of the universe which is under observation

  • The remaining portion of the universe which is not a part of the system is called the surroundings

  • The system is separated by real or imaginary boundaries.



homogeneous

  • homogeneous





Extensive

  • Extensive

  • (m, V, U, H, G, S, c)

  • The properties of the system whose value depends upon the amount of substance present in the system



Classification

  • Classification

  • of a process according to the constant parameter of a system are:

  • Isothermic process – temperature is constant, T=const

  • Isochoric process – volume is constant V = const.

  • Isobaric process – pressure of the system is constant, p = const

  • Adiabatic process – the system is completely isolated from the surroundings. For an adiabatic (Q=0) system of constant mass, ▲U=W



Exothermic process is a process that releases energy as heat into its surroundings. We say that in an exothermic process energy is transferred ‘as heat’ to the surroundings. For example: a reaction of neutralization (acid + basic).

  • Exothermic process is a process that releases energy as heat into its surroundings. We say that in an exothermic process energy is transferred ‘as heat’ to the surroundings. For example: a reaction of neutralization (acid + basic).

  • Endothermic process is a process in which energy is acquired from its surroundings as heat. Energy is transferred ‘as heat’ from the surroundings into the system. For example: the vaporization of water



Reversible process is a process in which the direction may be reversed at any stage by merely a small change in a variable like temperature, pressure, etc.

  • Reversible process is a process in which the direction may be reversed at any stage by merely a small change in a variable like temperature, pressure, etc.

  • Irreversible process is a process which is not reversible. All natural process are irreversible



State function (thermodynamic function)

  • State function (thermodynamic function)

  • Internal energy U [J/mol]

  • Enthalpy H [kJ/mol] or [kJ]

  • Entropy S [J/mol K] or [J/K]

  • Gibbs energy G [J/mol] or [J]

  • ΔU = U(products) – U(reactants)



State function depends only upon the initial and final state of the system and not on the path by which the change from initial to final state is brought about.

  • State function depends only upon the initial and final state of the system and not on the path by which the change from initial to final state is brought about.



It is the sum of different types of energies associated with atoms and molecules such as electronic energy, nuclear energy, chemical bond energy and all type of the internal energy except potential and kinetic energies.

  • It is the sum of different types of energies associated with atoms and molecules such as electronic energy, nuclear energy, chemical bond energy and all type of the internal energy except potential and kinetic energies.









Enthalpy H

  • Enthalpy H

  • A thermodynamic function of a system, equivalent to the sum of the internal energy of the system plus the product of its volume multiplied by the pressure exerted on it by its surroundings.

  • ▲H = ▲U + p▲V



The meaning of the state functions in the thermodynamic processes

  • The meaning of the state functions in the thermodynamic processes

  • Exothermic process

  • Qv > 0, ▲U < 0

  • Qp > 0, ▲H < 0

  • Endothermic process

  • Qv < 0, ▲U > 0

  • Qp < 0, ▲H > 0



Matter/energy may be altered (converted), but not created (from nothingness) nor destroyed (reduced to nothingness).

  • Matter/energy may be altered (converted), but not created (from nothingness) nor destroyed (reduced to nothingness).

  • The First Law teaches that matter/energy cannot spring forth from nothing without cause, nor can it simply vanish.

  • Energy can neither be created nor destroyed although it may be converted from one form to another.

  • The given heat for the system spends on the change of the internal energy and producing the work:

  • Q = ▲U + W





The study of the energy transferred as heat during the course of chemical reactions.

  • The study of the energy transferred as heat during the course of chemical reactions.

  • Thermochemical reactions:

  • H2(g) + Cl2(g) = 2HCl; ▲ H = -184,6 kJ

  • 1/2 H2(g) + 1/2 Cl2(g) = HCl; ▲ H = -92,3 kJ/mol

  • ▲ H is calculated for 1 mole of product









Second Law of Thermodynamics (refrigerator): It is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish this flow.

  • Second Law of Thermodynamics (refrigerator): It is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish this flow.



The amount of molecular randomness in a system is called the system’s entropy (S).

  • The amount of molecular randomness in a system is called the system’s entropy (S).

  • Entropy is a measure of randomness or disorder of the system



The maximum amount of energy available to a system during a process that can be converted into useful work

  • The maximum amount of energy available to a system during a process that can be converted into useful work

  • It’s denoted by symbol G and is given by

  • ▲G = ▲H - T ▲S

  • where ▲G is the change of Gibbs energy (free energy)

  • This equation is called Gibbs equation and is very useful in predicting the spontaneity of a process.

  • N.B. Gibbs equation exists at constant temperature and pressure



  • 1) Spontaneous (irreversible) process :

  • ▲ G < 0, ▲S > 0, ▲H < 0

  • 2) Unspontaneous (reversible) process :

  • ▲ G > 0, ▲S < 0, ▲H > 0

  • 3) Equilibrium state

  • ▲ G = 0







Chemical kinetics is that branch of chemistry, which deals with the study of the the rates of chemical reactions, the factors affecting the rates of the reactions and the mechanism by which the reactions proceed.

  • Chemical kinetics is that branch of chemistry, which deals with the study of the the rates of chemical reactions, the factors affecting the rates of the reactions and the mechanism by which the reactions proceed.



Simple reactions

  • Simple reactions

  • go in a one elementary

  • chemical act



Primary process – chain initiating step (stage):

  • Primary process – chain initiating step (stage):

  • h

  • Cl2 === 2С1.

  • chlorine molecule absorbs one quantum of light (h) and dissociates to give Cl atoms.

  • Secondary process – chain propagating step (stage):

  • 1. Cl. + Н2 = HCl + H.

  • 2. H. + Cl2 = HCl + Cl.

  • Third process – chain terminating step (stage):

  • Сl. + Cl. = Сl2



For example: Phenol with nitric acid, so have been formed ortho-, pair- and meta-nitrophenol.

  • For example: Phenol with nitric acid, so have been formed ortho-, pair- and meta-nitrophenol.



reactions which are flowing past in two parties: the forward reaction - conducts to formation reaction product and reverse reaction - decomposing reaction product on mother substances.

  • reactions which are flowing past in two parties: the forward reaction - conducts to formation reaction product and reverse reaction - decomposing reaction product on mother substances.

  • k1

  • A + B + C = A1 + B1 + C1

  • k2













FACTORS WHICH INFLUENCE RATES OF CHEMICAL REACTIONS

  • FACTORS WHICH INFLUENCE RATES OF CHEMICAL REACTIONS

  • Concentration of the reacting species.

  • Temperature of the system.

  • Nature of the reactants and products.

  • Presence of a catalyst.

  • Surface area.

  • Exposure to radiation.



Concentration of the reactants.

  • Concentration of the reactants.

  • The rate of a reaction is directly proportional to the concentration of the reactants.



The rate of reaction is proportional to the concentrations of reactants raised to а power.

  • The rate of reaction is proportional to the concentrations of reactants raised to а power.

  • A + B = C;  = k[A][B]

  • equation of the rate laws

  • 3H2+N2 =2NH3;  = k[H2]3[N2]

  • The coefficient k is called the rate constant for the reaction or velocity constant. The rate constant is independent of the concentrations but depends on the temperature.

  • [A] = [B] = 1 mole/liter, then rate = k







Arrhenius Equation

  • Arrhenius Equation

  • It is a well-known fact that raising the temperature increases the reaction rate.

  • E a = activation energy R = 8.314 [ J · mol -1 · K -1 ] T = absolute temperature in degrees Kelvin A = pre-exponential or frequency factor A = p · Z, where Z is the collision rate and p is a steric factor. Z turns out to be only weakly dependant on temperature. Thus the frequency factor is a constant, specific for each reaction.



4. Presence of a catalyst. A catalyst is a substance which influences the rate of a reaction without undergoing any chemical change itself. It has been observed that many reactions are made to proceed at an increased rate by the presence of certain catalysts.

  • 4. Presence of a catalyst. A catalyst is a substance which influences the rate of a reaction without undergoing any chemical change itself. It has been observed that many reactions are made to proceed at an increased rate by the presence of certain catalysts.

  • 5. Surface area.

  • The large the surface area of the reactants, the faster is rate of reaction. It has been observed that if one the reactants is a solid, then the rate of the reaction depends upon the state of sub-division of the solid.

  • 6. Exposure to radiation.

  • In some cases, the rate is considerably increased by the use of certain radiations. For example, reaction of hydrogen and chloride takes place very slowly in the absence of light. However, in the presence of light, the reaction takes place very rapidly.





1. Homogeneous catalysts.

  • 1. Homogeneous catalysts.

  • If the catalyst is present in the same phase as the reactants, it is called а homogeneous catalyst and this type of catalysis is called homogeneous catalysis.

  • NO(g)

  • 2 SO2(g) + О2(g) ===== SO3(g)

  • Н+ (aq)

  • CH3COOC2H5(l)+Н2О(l)=====СНЗСООН(l)+C2H5OH(1)

  • Н+ (aq)

  • С12Н22О11(aq)+Н2О(1)====С6Н12О6(aq)+С6Н12О6 (aq)

  • Sucrose Glucose Fructose



If the catalyst is present in а different phase than the reactants, it is called а heterogeneous catalyst and this type of catalysis is called heterogeneous catalysis.

  • If the catalyst is present in а different phase than the reactants, it is called а heterogeneous catalyst and this type of catalysis is called heterogeneous catalysis.

  • Pt, 8000С

  • 4NH3 + 5O2 ======== 4NO + 6Н2O





Enzymes Substance that acts as a catalyst in living organisms, regulating the rate at which life's chemical reactions proceed without being altered in the process.

  • Enzymes Substance that acts as a catalyst in living organisms, regulating the rate at which life's chemical reactions proceed without being altered in the process.

  • Enzymes are classified by the type of reaction they catalyze:

  • Oxidation-reduction

  • Transfer of a chemical group

  • Hydrolysis

  • Removal or addition of a chemical group

  • Isomerization

  • Polymerization



Influence on the activity of enzymes:

  • Influence on the activity of enzymes:

  • 1. Enzyme activity can be affected by other molecules.

  • Inhibitors are molecules that decrease enzyme activity;

  • If a competing molecule blocks the active site or changes its shape, the enzyme's activity is inhibited. If the enzyme's configuration is destroyed (denaturated), its activity is lost.

  • Activators are molecules that increase activity.

  • Many drugs and poisons are enzyme inhibitors.

  • 2. Activity is also affected by temperature

  • 3. Chemical environment (pH). 4. The concentration of substrate.






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