CHE 312 Lecture 1
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Transcript of CHE 312 Lecture 1
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CHE 312Chemical
Engineering Thermodynamics II
Credit Hours 3 – 0
By Dr. Qazi Nasir
Lecture # 1
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CHE 312 Chemical Engineering Thermodynamics II• In nineteenth century, the science of thermodynamic was
born which describe the operation of steam engines
• The name was given as power developed from heat is the main application of steam engine
• The principle which valid for engines are generalized as first and second laws of thermodynamics
• These laws have no mathematical sense
• Chemical engineers among other problems , calculation of heat and work requirement for physical and chemical processes, determination of equilibrium conditions for chemical reactions and transfer of chemical species between phases
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CHE 312 Chemical Engineering Thermodynamics II• The application of thermodynamics to any real problems
starts with the identification of body
• Body = system
• Thermodynamic state = Measurable macroscopic properties such as length , time, mass, temperature and amount of substance (Mass, no of moles, total volume, specific volume)
• Temperature: commonly measured in liquid-in-glass thermometer, wherein the liquid expands when heated
• Pressure: The normal force exerted by the fluid per square meter or Nm-2. (dead-weight gauge)
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CHE 312 Chemical Engineering Thermodynamics IIWork: when a force acts through a distance then work is performed
• A work which accompanies a change in volume of fluid is often encountered in thermodynamics, e.g. compression and expansion of fluid in a cylinder
• The force exerted by the piston on the fluid is equal to the product of the piston area and pressure of the fluid.
• The displacement of the piston is equal to the total volume change of the fluid divided by area
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CHE 312 Chemical Engineering Thermodynamics II
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CHE 312 Chemical Engineering Thermodynamics IIArea is constant
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CHE 312 Chemical Engineering Thermodynamics IIHeat: Hot object brought in contact with cold object becomes cooler whereas cooled object become warmer.
• Something is transferred from hot object to cold object is Heat Q
• Temperature is a driving force for the transfer of energy as heat
• Rate of heat transfer from one body to another is proportional to the temperature difference. Between two bodies
• 1/100th quantity of heat which when transferred to one kilogram mass of water raised its temperature from 0 to 100 0C
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CHE 312 Chemical Engineering Thermodynamics IIThermodynamic properties are classified into two types
Direct measureable properties
• Pressure-volume-temperature (PVT) relationships
Indirect measureable properties
• Determined indirectly using relationships that express in terms of physical properties
• Internal energy, entropy, enthalpy, Helmholtz free energy, Gibbs free energy and association properties such as chemical potential and fugacity)
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CHE 312 Chemical Engineering Thermodynamics II
Four quantities called ‘thermodynamic potential’ are useful
in the chemical thermodynamics of reactions and non-
cyclic processes.
• Internal energy
• Enthalpy
• Helmholtz free energy
• Gibbs free energy
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CHE 312 Chemical Engineering Thermodynamics IIHelmholtz Free Energy
• Internal energy U might be thought of as the energy required to create the system in the absence of changes in temperature or volume
• But in environment of temperature T, some the energy can be obtained by spontaneous heat transfer in TS
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CHE 312 Chemical Engineering Thermodynamics IIGibbs Free Energy
• Internal energy U might be thought of as the energy required to create the system in the absence of changes in temperature or volume
• Amount of work PV must be done if the system is created from a very small volume.
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CHE 312 Chemical Engineering Thermodynamics IIFugacity
• In chemical thermodynamics, the fugacity (f) of a real gas is effective pressure which replaces the true mechanical pressure in accurate chemical equilibrium calculations.
• For example, nitrogen gas (N2) at 00C and a pressure of P = 100 atm has a fugacity of f = 97.03 atm
• This also means the chemical potential of real nitrogen at a pressure of 100 atm is less than if nitrogen were an ideal gas.
• Fugacities are determined experimentally or estimated from various model
• The ideal gas pressure and fugacity are related through fugacity coefficient
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CHE 312 Chemical Engineering Thermodynamics IIFundamental equations
J. W. Gibbs give the names because they contain all information needed for the complete description of the thermodynamic state of a system.
Fundamental equations for closed system
System that do no exchange mass with the surroundings is considered as closed system
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CHE 312 Chemical Engineering Thermodynamics IIFundamental equations for the Internal EnergyA closed homogenous system which experience the transfer of a small of heat dQ and an amount of volumetric work dW. The change in internal energy according to first law is given as
dU = dQ – dW (1)
If changes are reversible, then:
dW = PdV ; dQ = TdS
dU = TdS – PdV
U = f(S, V)
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CHE 312 Chemical Engineering Thermodynamics IIFundamental equations for the Internal Energy
Consider a differential change in S and V. The corresponding change in U is given as.
Comparison of equation (1) indicates that
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CHE 312 Chemical Engineering Thermodynamics IIThe system enthalpy is also specified from the definition
H = U + PV
Similarly, the two energy properties
A = U – ST
Gibbs free energy
G = U + PV - ST
Therefore, the availability of the functional relationship U = f(S,V) gives complete description on the thermodynamic state of the system i.e. its fundamental equation
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CHE 312 Chemical Engineering Thermodynamics IIThe fundamental Equation for H, A, and G
H = U + PV (2)
The enthalpy differential
dH = dU + PdV + VdP
As, TdS = dU + PdV
dH = TdS + VdP
which indicates that:
H = f(S,P) (3)
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CHE 312 Chemical Engineering Thermodynamics IIThe differential change in S and P leads to following form
Comparison with Eq (2) indicates that
(4)
Eq (3) and Eq (4) completely describe the system once S and P are specified. It is therefore, also a fundamental equation
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CHE 312 Chemical Engineering Thermodynamics IISimilarly, Helmholtz & Gibbs free energy can be describe as
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CHE 312 Chemical Engineering Thermodynamics II• Recommended Books
• Smith J.M., Van Ness H.C., Abbott M.M. “Chemical Engineering Thermodynamics” 6th Ed. 2001. McGraw Hill International Edition.
• Daubert Thomas E. “Chemical Engineering Thermodynamics”, 1st Ed. 1985, McGraw Hill Book Company.
• Sandler Stanley I. “Chemical and Engineering Thermodynamics” 3rd Ed. John Wiley and sons, Inc.