Topics To Be Discuss• Introduction and Fundamentals of Thermodynamics (Chapter 1)• The First Law of Thermodynamics for Close and Open Systems

(Chapter 2)• Equation of State (Chapter 3)• Heat Effects (Chapter 4)• The Second Law of Thermodynamics (Chapter 5)• Thermodynamic Properties of (Pure) Fluid (Chapter 6)• Production of power from heat (Chapter 8)• Refrigeration & Liquefaction (Chapter 9)• Vapour-Liquid Equilibrium (Chapter 10)• Theory of Solution Thermodynamics (Chapter 11)• Chemical Reaction Equilibrium (Chapter 13)

Thermodynamics

Science of Energies.Study of science of transfer & Conversion of

Energies from one form to another and the study of properties and characteristics of matter needed for this transference.

Greek words: therme (heat) + dynamis (power)

Thermodynamics Power developed from heat

Types Of ThermodynamicsClassical thermodynamics formulate the

macroscopic stateStudies the average behavior of large groups of

MoleculesDefines macroscopic properties such as

temperature and pressure.Statistical thermodynamics formulate the

microscopic stateDefines the properties of a system based on the

behavior of molecules/atoms.

Chemical engineer & thermodynamics

Calculation of heat and work requirements for physical and chemical processes

Determination of equilibrium conditions forChemical reactionsTransfer of chemical species between phases (mass

transport)Thermodynamicsdeals with driving forcedoes not deal with RATEs of physical or chemical

phenomenaRate=f(driving force, resistance)

Basic Thermodynamic definitions A system contains a substance with a large amount of molecules or

atoms, and is formed by a geometrical volume of macroscopic dimensions subjected to controlled experimental conditions

A simple system is a single state system with no internal boundaries, and is not subject to external force fields or inertial forces

A composite system has at least two simple systems separated by a barrier restrictive to one form of energy or matter

The boundary of the volume separates the system from its surroundings

A system may be taken through a complete cycle of states, in which its final state is the same as its original state

Closed and Open systems

Closed system: Material content is fixed Internal mass changes only due to a chemical reaction Exchange energy only in the form of heat or work with the surroundings

Open system: Material and energy content are variable Systems freely exchange mass and energy with their surroundings

Other systems

Isolated system:Cannot exchange energy and matterThermally insulated system:System surrounded by an insulating boundaryUniverse:A system and its surroundings

Processes Energy conversion and degradation: physical and chemical processes “A process takes place in a system!” Adiabatic process: Any process within an adiabatic system (no heat transfer through the

system boundaries) Steady state process: Input = Output Variables in the system remain constant with time System exchanges energy or matter at a constant rate Unsteady state process (transient process): Variables in the system change with time Input = output + Accumulation Infinitesimal process: A process that takes place with only an infinitesimal change in the

macroscopic properties of a system

Thermodynamic properties

are derived from the statistical averaging of the observable microscopic coordinates of motion

If a thermodynamic property is a state function its change is independent of the path between

the initial and final statesdepends on only the properties of the initial and

final states of the systemThe infinitesimal change of a state function is an

exact differential

What do we mean by the State of a System?

The state of a system is fixed by knowing a minimum number of the system properties

EXTENSIVE are additive and depend upon the mass of the system, e.g. m, n, V,

H, U, etc. All extensive properties are homogeneous functions of the first

order in the mass of the system Ex: Doubling the mass of a system at constant composition doubles

the internal energy INTENSIVE are not additive and do not depend upon the mass of the

system,e.g. P, T, refractive index, density, thermal conductivity, etc. Intensive properties can be expressed as derivatives of extensive

properties

Energy Mechanical work of expansion or compression proceeds with the observable motion of the coordinates of

the particles of matter Chemical work proceeds with changes in internal energy due to changes in the chemical composition (mass

action) Potential energy is the capacity for mechanical work related to the position of a body Kinetic energy is the capacity for mechanical work related to the motion of a body Potential and kinetic energies are external energies Sensible heat and latent heat are internal energies

State Of Equilibrium

We only Apply Thermodynamics at equilibriumMechanical Equilibriumno unbalanced forcesChemical Equilibriumno chemical potential differencesThermal Equilibriumno temperature differencesPhase EquilibriumNo phase change

MechanicalEquilibrium

Zeroth Law

Object A is in equilibrium with both the thermometer and object B. Then the thermometer should also be in equilibrium with object B.

This means all three objects have the same temperature

Temperature scales

Ideal Gas Thermometer

t (C)

f (t)

Limit (pV) p 0

100 C0 C-273.15 C

Substance – gasProperty – limit(pV) Reference pointInterpolation

f (t)= pV=0

Absolute Zerof(t) = Pv at triple point of water T = 22711.8 273.15 K 273.15K

Slope R

Triple point of water

Work: P-V

Internal Energy U

No concise thermodynamic definitionCannot be directly measuredOnly absolute values are known(no reference point)In thermodynamics, only changes in internal

energy are used ΔU=U2-U1

First law of thermodynamics:Conservation of energy

During a process:Energy can be transferred and converted

from one form to another, while the total energy remains constant

(Energy of the system) + (Energy of the surroundings) = 0

Finite change in quantity

First law of thermodynamics

Example 2.4 (Ref: Smith,Van Ness, Abbott, 7th ed, p28)

When a system is taken from state a to state b in Fig. 2.1 along path acb, 100 J of heat flows into the system and the system does 40 J of work.

a) How much heat flows into the system along path aeb if the work done by the system is 20 J?

b) The system returns from b to a along path bda. If the work done on the system is 30 J, does the system absorb or liberate heat? How much?

James Prescott Joule’s experiment

Problem 2.5 (Ref: Smith,Van Ness, Abbott, 7th ed, p56)

One mole of gas in a closed system undergoes a four-step thermodynamic cycle. Use the data given in the following table to determine numerical values for the missing quantities.

Constant-V and Constant-P Process

• Energy balance for n moles of a homogeneous fluid contained in a closed system:

• d(nU) = dQ + dW• Mechanically reversible, closed system:• dW = -Pd(nV)• Then d(nU) = dQ - Pd(nV)

@ Constant-V

• If V = cnst dV = 0• for closed system dn = 0 dW = -Pd(nV) = 0• Then

• Closed, constant volume system:• Heat transferred = Change in internal energy

@ Constant-P

reversible, closed, constant pressure system:Heat transferred = Change in enthalpy

Enthalpy

Is used to calculate cooling and heating processes (heat exchangers, evaporators, distillation columns, pumps, turbines, engines, etc) appears in energy balances to calculate Q and W

Ex: Enthalpy of moist and humid air sensible heat + latent heat

Example 2.8(Ref: Smith,Van Ness, Abbott, 7th ed, p39)

Calculate ΔU and ΔH for 1 kg of water when it is vaporized at 100 °C and 101.33 kPa. Specific volumes of liquid and vapor water at these conditions are 0.00104 and 1.673 m3/kg. 2256.9 kJ of heat is added to water for it to vaporize.

Solution:System: 1 kg water @ constant TAssumption: Mechanically reversible, closed, constant P systemΔH = Q = 2256.9 kJΔH = ΔU + Δ(PV) ΔU = ΔH – PΔVPΔV = 101.33 kPa * (1.673-0.00104) m3 =169.4 kJΔU = 2256.9 - 169.4 = 2087.5 kJ

Heat capacity @ constant V

Heat capacity @ constant P

General Energy Balance

Control volume with one entrance-exit

COMPRESSIBILITY FACTOR—A MEASUREOF DEVIATION FROM IDEAL-GAS

BEHAVIORCompressibility factor Z A factor that accounts for the deviation of real gases from ideal-gas behavior at a given temperature and pressure.

The farther away Z is from unity, the more the gas deviates from ideal-gas behavior.

Gases behave as an ideal gas at low densities (i.e., low pressure, high temperature).

Question: What is the criteria for low pressure and high temperature?

Answer: The pressure or temperature of a gas is high or low relative to its critical temperature or pressure.

35Comparison of Z factors for various gases.

Reduced temperature

Reduced pressure

Pseudo-reduced specific volume Z can also be determined from

a knowledge of PR and vR.

Corresponding State Two Parameter

Principle of Corresponding States

Lennard-Jones (LJ) 12/6 pair-potential

Interaction forces that exist between molecules of any substance, typically at very short intermolecular separation distances (~ 5 – 20A(where 1A= 10-8m)

If the centre of total positive and negative charges in a molecule do not coincide (for example, for water), it results in a permanent dipole, which imparts a polarity to the molecule.

B/ r

A/r −6

−12

Molecules for which the centres of positive and negative charge coincide (for example, methane) do not possess a permanent dipole and are termed non-polar. When two polar molecules approach each other closely the electric fields of the dipoles overlap, resulting in their re-orientation in space such that there is a net attractive force between them.

When molecules approach to distances even less than ~ 5 A or so, a repulsive interaction force comes into play due to overlap of the electron clouds of each molecule, which results in a repulsive force field between them.

Virial EOS

Generally applicable to moderate deviations from ideal gas behavior, the virial EOS is given by two alternate forms:

Pitzer Correlation

Acentric Factor “The compressibility factor for all fluids with the same value of ω, when compared at the same reduced temperature and pressure are approximately the same, and hence the deviation from ideal-gas behavior is nearly the same.”

Generalized Compressibility factor Approach to EOS: Pitzer Correlations

41

OTHER EQUATIONS OF STATESeveral equations have been proposed to represent the P-v-T behavior of substances accurately over a larger region with no limitations.

Van der Waals Equation of State Critical isotherm

of a pure substance has

an inflection point at the

critical state.

This model includes two effects not considered in the ideal-gas model: the intermolecular attraction forces and the volume occupied by the molecules themselves. The accuracy of the van der Waals equation of state is often inadequate.