Farmasi Fisika I-Thermodynamics

FARMASI FISIKA I

Termodinamika

Thermodynamics

Why thermodynamics are important in pharmacy?

Thermodynamics is concerned with the quantitative relationships between heat and other forms of energy. including mechanical, chemical, electric, and radiant energy

Describing energy-related changes in reaction

Determining the fate of simple chemical processes to describing the very complex behavior of biologic cells

Energy

Voltage source

Energy can be considered as the product of

an intensity factor and a capacity factor.

Stated more explicitly, the various types of energy may be

represented as a product of an intensive property independent

of the quantity of material, and the differential of an extensive

property that is proportional to the mass of the system.

Mechanical Energy

A body is said to possess kinetic energy because of its motion or the motion of its parts (i.e., its molecules, atoms, and electrons),

and to possess potential energy by virtue of its position or the configuration of its parts.

It is not possible to know the absolute value of the energy of a system; it is sufficient to record the changes in energy that occur

when a system undergoes some transformation.

Basic Definitions of Thermodynamics

A system is a well-defined part of the universe The system is separated from surroundings, by physical or virtual

boundaries Work is a transfer of energy that can be used to change the height

of a weight somewhere in the surroundings Heat is a transfer of energy resulting from a temperature difference

between the system and the surroundings Both work and heat only appear at the systems boundaries where

the energy is being transferred

The First Law of Thermodynamics

The first law is a statement of the conservation of

energy. It states that, although energy can be

transformed from one kind into another, it cannot be

created or destroyed.

The total energy of a system and its immediate

surroundings (which together are often referred to as

an isolated system) remains constant during any

operation.

The First Law

A close system is one that may

exchange heat and work but not

matter with its surroundings

An open system involved a transfer

of matter in addition to the

exchange of heat and work


According to the first law, the change in internal energy (E) is

related to heat (Q) and work (W) transferred between the

system and its surroundings

E = E2 + E1 = Q + W

E2 = internal energy of the system in its final state

E1 = internal energy of the system in its initial state of the atoms, ions, or

molecules of

The internal energy is related to the microscopic motion of

which the system is composed


By using E = E2 + E1 = Q + W equation, the change of internal

energy can be evaluated by measuring Q and W during the

change of state.

Infinitesimal change in the energy dE is written

dE = dq + dw

Where dq is the heat absorbed and dw is the work done during infinitesimal

change of the system


Isothermal and adiabatic processes

When the temperature is kept constant during a process, the

reaction is said to be conducted isothermally

When heat is neither loss or gained during a process, the

reaction is said to occur adiabatically

In adiabatic process dq = 0 therefore,

dw = dE When work is done by the system, the internal energy decreases, and

because heat cannot be absorbed in adiabatic process, the temperature must

fall.

The work dependent only on the initial and final states of the system.

The First Law of Thermodynamics WORK OF EXPANSION AGAINST A CONSTANT PRESSURE

A vapor confined in a hypothetic cylinder fitted with a weightless, frictionless piston of area A. If a constant external pressure P is exerted to the piston, the total force is P x A. The vapor in the cylinder is now made to expand by increasing the temperature, and the piston moves to the distance h. The work done against the opposing pressure is W = P x A x h A x h is the increase in volume V = V2 V1 Therefore at constant pressure W = P V


Reversible processes A process which is always in a state of virtual thermodynamic

equilibrium, being reversed by an infinitesimal change of

pressure, it is said to be reversible.

If the pressure on the system is increased or decreased rapidly, or

if the temperature of the bath cannot adjust instantaneously to

the change in the system, the isolated system is not in the same

thermodynamic state at each moment, and the process is

irreversible

Exercise : Application of the first law of thermodynamics


Maximum work

The work done by a system in an isothermal process

is at a maximum when it is done reversibly.

What is the maximum work done in the isothermal reversible expansion of 1 mole of an ideal gas from 1 to 1.5 liters at 25C?

Wmax = - n RT ln (V2/V1)

Ideal gas equation PV = nRT R is the gas constant 8.31451 J K-1 mol-1 1.98722 cal K-1 mol-1

Thermochemistry

Many chemical and physical processes are carried out at atmospheric (essentially constant) pressure. Under this condition the work of expansion is done at constant pressure, the heat exchanged equals to the change in enthalpy. W = - P V = - P (V2 - V1) E = Q + W E = Qp - P (V2 - V1) Qp is the heat absorbed at a constant pressure Qp = E2 - E1 + P (V2 - V1) Qp = E2 + PV2 - E1 + PV1 Qp = H (negative = exothermic, positive = endothermic)

enthalpy H

The increase in enthalpy H is equal to the heat absorbed at constant pressure The change in enthalpy accompanying a chemical reaction remains a function only of temperature.

Thermochemistry The formation of methane: C(s) + 2H2(g) == CH4(g) Hf(25C) The combustion of methane: CH4(g) + 2O2(g) == CO2(g) + 2H2O(l) Hcomb(25C) = -212.8 kcal CO2(g) + 2H2O(l) == CH4(g) + 2O2(g) Hcomb(25C) = +212.8 kcal C(s) + O2(g) == CO2(g) Hf(25C) = -94.052 kcal 2(H2(g) + 1/2O2(g) == H2O(l)) 2 (Hf(25C) = -68.317 kcal) ___________________________________________________

C(s) + 2H2(g) == CH4(g)

Hf(25C) CH4(g) = -Hcomb + Hf CO2(g) + 2 x Hf (H2O(l)) = 212.8 kcal + (-94.052 kcal) + 2(-68.317 kcal) = -17.886 kcal

Exercise: Thermochemistry

If breaking C=C bond requiring 130 kcal, breaking Cl-Cl bond requiring 57 kcal, formation of C-C bond liberating 80 kcal and formation of C-Cl liberating 78 kcal of energy. What is the enthalpy change H of the reaction of ethene and chlorine into dichlorethane? 1 cal = 4.184 joules

The Second Law of Thermodynamics

o The first law of thermodynamics observed that energy must be conserved when it is converted from one to another not about the probability that a process will occur.

o The second law refers to the probability of the occurrence of a process based of the observed tendency of a system to approach a state of energy equilibrium

o Heat flows spontaneously only from hotter to colder bodies, and a steam engine can do work only with a fall in temperature and a flow of heat to the lower temperature.

o No useful work can be obtained from heat at constant temperature


o Gases expand naturally from higher to lower pressures, and solute molecules diffuse from a region of higher to lower concentration.

o These spontaneous processes will not proceed in reverse without the intervention of some external agency.

o Although spontaneous processes are not thermodynamically reversible (irreversible), they can be carried out in a nearly reversible manner by an outside agency.


o The energy that may be freed for useful work in a gas, liquid, or solid, or any reaction mixture, is known as the free energy of the system.

o The free energy decreases as a physical or chemical reaction proceeds.

o In general, spontaneous processes at constant temperature and pressure are accompanied by a loss in free energy, and this decrease signifies the natural tendency for the transformation to occur.


o An important consideration is that of the possibility of converting heat into work.

o Not only is heat isothermally unavailable for work; it can never be converted completely into work.

o The spontaneous character of natural processes and the limitations on the conversion of heat into work constitute the second law of thermodynamics.

The Second Law of Thermodynamics The efficiency of the heat engine

Exercise: The second law of thermodynamics

What is the entropy change S accompanying the vaporization of 1 mole of water in equilibrium with its vapor at 25C. This is a reversible and isothermal process and carried out at a constant pressure. The heat of vaporization Hv required to convert the liquid to the vapor state is 10,500 cal/mole.

The Third Law of Thermodynamics

o The third law of thermodynamics states that the entropy of a pure crystalline substance is zero at absolute zero because the crystal arrangement must show the greatest orderliness at this temperature.

o The third law cannot be applied to supercooled liquids because their entropy at 0 K is probably not zero.

Exercise

H and S for the transition from liquid water to ice at -10C and at 1 atm pressure are 1343 cal/mole and -4.91 cal/mole deg, respectively. What is the G for the phase change at this temperature and indicate whether this process is spontaneous?

The Third Law of Thermodynamics FREE ENERGY FUNCTIONS AND APPLICATIONS

o Two new thermodynamic properties, the Gibbs free energy G and the Helmholtz free energy or work function A are now introduced, and some applications of these important functions to chemistry and pharmacy are considered.

o These functions may be related to the other thermodynamic quantities in the following way. Disregarding electric and other forms of energy, we consider PV work as the only useful work or external energy that a system can accomplish.


The heat content or total energy of the system is then divided into internal and external energy:

H = E + PV Total Internal External energy energy energy

The total heat maybe divided into isothermally available or free energy G and isothermally unavailable energy TS

H = G + TS Total isothermally isothermally energy available unavailable energy energy


Finally, the internal can be divided into isothermally available internal energy or work function A and isothermally unavailable energy TS.

Thus, for an isothermal process

E = A + TS Internal isothermally isothermally energy available unavailable internal energy energy


A number relationships maybe obtained by rearranging these quantities and placing various restrictions on the processes described

G = H - TS G = E + PV - TS G = A + PV

Exercise

What is the free energy change when 1 mole of an ideal gas is compressed from 1 atm to 10 atm Determine the change in the entropy, Helmholtz free energy, and Gibbs free energy, when a mole of ideal gas is compressed from 1atm to 100 atm at 20C. What is the free energy change when the kidneys transfer various chemical constituents at body temperature from the blood plasma to the more concentrated urine. The concentration of urea in the plasma is 0.005 mole/liter; in the urine is 0.333 mole/liter. Calculate the free energy change in transporting 0.1 mole of urea from the plasma to the urine.

Exercise

If the molar concentration of a monomeric species of Sodium cholate at 25C is 4 x 10-3 mole/liter and the concentration of dimeric species is 3.52 x 10-5 mole/liter, what is the equilibrium constant and the standard free energy for the dimerization process?

The Laws of Thermodynamics

The First Law of Thermodynamics Energy is conserved; it can be neither created nor destroyed

The Second Law of Thermodynamics In an isolated system, natural processes are spontaneous when

they lead to an increase in disorder, or entropy

The Third Law of Thermodynamics The entropy of a perfect crystal is zero when the temperature of

the crystal is equal to absolute zero

Documents

Farmasi Fisika I-Thermodynamics