What is Thermodynamics

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What is Thermodynamics     1. Understanding why
things happens   2. Concerning heat, work,
related temperature, pressure, volume and
equilibrium      3. Equations relate macroscopic
properties
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The laws of thermodynamics    
 
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       Study of heat engines        Being
studied by all students in physical science and
engineering
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Concept of State        
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From Avogadros hypothesis the volume per mole of
all ideal gases at 0oC and 1atm pressure is
22.414 litres.  
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For n mole gas PVnRT
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For water vapour, the number of moles for Kg
water is obtained by  
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Thermodynamics Process Work and Energy Heat
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1. Open system- material and energy exchange
2. Closed system- energy exchange only
3. Isolated system- no material and energy exchange

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What we learn from this module?       1.Internal
energy U and entropy S   2.Combining U and S with
P, T and V gives enthalpy HU PV and Gibbs
energy GH-TS     3.?H is related to heat
adsorption or release at constant pressure 4. G
controls the position of equilibrium in closed
systems at constant temperature and pressure.  
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Why is Thermodynamics useful?   1.Qualitative
explanation of materials behaviour   2.Quantitativ
ely understanding of materials status. 3.
Physical significance of thermodynamic functions.

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Applications of Thermodynamics     1.Extraction,
refining   2.Corrosion   3.Phase
transformation-phase diagram calculation     4.Mat
erials processing   5.Design of new materials.
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The First Law of Thermodynamics       
Conservation of Energy Principle      Same
principle in mechanics, physics and
chemistry    
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Work done in an Expansion (or contraction)
against an External Pressure    
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Expansion against a constant external
pressure      

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W12
Q12
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Reversible process and Maximum Work Reversible
process for a closed system    W
system-environment W environment-system Q
environment-system Q system-environment    
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For an ideal gas          
For isothermal process, ie. Tconstant
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Thermodynamics tutorial on the 24th of Oct
(Tuesday) From 2pm D14
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• Questions
• How to calculate W for a constant pressure
  process?
• How to calculate W for an isothermal reversible
  process?
• Is a constant pressure process an reversible
  process? Explain why?
• All of these questions are concerned with ideal
  gas systems.

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Example Gas compress during quasi-equilibrium
processing, with PVconstant. The system is the
gas   P1101325 N/m2, V10.01m3,
V20.005m3   Find W
W-702J
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Enthalpy   ?Uq-w       Q Heat is transferred
due to the presence of a temperature
difference.     Work here is considered as the
work of expansion.     U results from the
oscillation of atoms or ions in solid and
movement of the particles in gas and
liquid.     Q and w depend on how the change is
carried out where the difference between them
does not.     At constant volume, w0 and ?Uq
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Thursday lecture

• Sackville Street Building C9
• 11am-1200

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The Enthalpy Function
When Pconstant
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      At constant pressure, the change in
enthalpy is equal to the heat     The change of
enthalpy is independent of path. Q Does q or W
depend on path?     For the change involving
solids and liquids, ?H??U, but for gases,
?H??U Qexplain why?
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Example 1   Given pconstant101.3 kPa V11m3,
V22m3 Q12200kJ   Find a) ?U b) an expression
for Q12 in terms of thermodynamics properties for
a quasi-equilibrium process.
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Example 2.   Given TT1T2constant for the
process P1200 kPa, T1300K V12m3, V24m3 Find
a) W and b) Q W277KJ
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Heat Capacities (Cp and Cv)     a)                
      Under constant volume conditions Cv- all
heat supplied increases energy of
sample b)                     Under constant
pressure conditions Cp- Heat supplied increases
energy of sample and provides energy for work
performed.  
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Relation between Cv and U     The 1st Law    When
Vconstant     Therefore  
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For n moles of materials over small ranges in
temperature Cv?constant
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Relation between Cp and H   At constant
pressure             Over small range of T for
n moles of materials  
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Summary   At constant volume     At constant
pressure     Molar heat capacity at constant
pressure     Molar heat capacity at constant
volume  
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• Questions
• For a constant temperature process of an ideal
  gas, prove ?H?U.
• For a gas system, explain why Cp is larger than
  Cv?
• For a solid/liquid system, explain why Cp is
  close to Cv?
• What are the equations for calculating change of
  enthalpy and internal energy due to temperature
  change?