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Thermo
Dr. Nuri Solak, Asst. Prof.
http://web.itu.edu.tr/solaknu/
www.ninova.itu.edu.tr
http://web.itu.edu.tr/solaknu/
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11.09.2014 => Introduction, Definition of terms, Importance of thermodynamics in
metallurgical and materials eng.
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18.09.2014 => I. Law of thermodynamics, enthalpy, heat capacity, Kirchhoff equation
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25.09.2014 => Heat of reaction, Hess Law, temperature dependency of heat of reaction
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02.10.2014 => Combustion and fuel, adiabatic flame temperature
09.10.2014 => Adiabatic flame temperature
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16.10.2014 => Combustion and fuel, adiabatic flame temperature, Energy balance
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23.10.2014 => II. Law of thermodynamics, entropy, III. Law of thermodynamics,
variation of entropy as a function of temperature
30.10.2014 => 1. Mid-term
06.11.2014 =>Standard free energy, equilibrium constant.
13.11.2014 => Calculation of composition of reaction under equilibrium conditions,
Phase equilibrium in a one-component system
20.11.2014 => Standard free energy, equilibrium constant, calculation of composition of
reaction under equilibrium conditions, Phase equilibrium in a one-component system
27.11.2014 => Standard free energy, equilibrium constant, calculation of composition of
reaction under equilibrium conditions, Phase equilibrium in a one-component system
04.12.2014 => 2. Mid-term
11.12.2014 => Ellingham diagrams, Reduction reactions of oxides
What is Thermodynamics
• Thermodynamics is a science and, more importantly, an
engineering tool used to describe processes that involve
changes in temperature, transformation of energy, and
the relationships between heat and work.
• Thermodynamic is not only related to heat, it gives
interrelation between different forms of energy.
• Thermodynamics is derived from the Greek words therme,
meaning heat, and dynamis, meaning power.
• Thermodynamics is concerned only with the equilibrium
state of matter.
Basic Definitions
A thermodynamic system (sistem) is a quantity of
matter of fixed identity, around which we can draw
a boundary. The boundaries may be fixed or
moveable.
Piston (boundary) and gas (system)
Work or heat can be transferred across the system
boundary. Everything outside the boundary is the
surroundings (çevre).
Basic Definitions
Isolated system (Soyut ): “have walls or boundaries that
are rigid, do not permit transfer of mechanical energy,
perfectly insulating, and impermeable. They have a
constant energy and mass content.
Adiabatic systems (Adyabatik): Perfectly insulated
systems. No energy transfer but matter can be transferred.
Closed systems (kapalı): have walls that allow transfer of
energy in or out of the system but are impervious to
matter. They contain a fixed mass and composition, but
variable energy.
Open Systems (açık): have walls that allow transfer of both
energy and matter to and from the system.
Basic Definitions
Homogenous System:
A finite region in the physical system across
which the physical and chemical properties are
uniformly constant. It is also described as phase.
Heterogeneous System:
The system when it contains two or more
phases, e.g., coexisting of ice and water.
Extensive Materials Properties
An extensive property is a physical quantity whose
value is proportional to the size of the system it
describes.
• ENERGY !!!
• entropy
• enthalpy
• mass
• momentum
• volume
Instensive Materials Properties
It is a physical property of a system that does not
depend on the system size or the amount of
material in the system
• temperature
• density (or specific gravity)
• viscosity
• electrical resistivity
• hardness
• melting point and boiling point
• magnetization
Macroscopic & Microscopic Energy
• Potential energy and kinetic energy are macroscopic
forms of energy. They can be visualized in terms of
the position and the velocity of objects.
• In addition to these macroscopic forms of energy, a
substance possesses several microscopic forms of
energy. Microscopic forms of energy include those
due to the rotation, vibration, translation, and
interactions among the molecules of a substance. It
is so called internal energy due to atomic-molecular
motion.
E = U + KE + PE
E = total energy
U = Internal energy
If we calculate change in energy
dE = q – PdV - w
(other, special conditions)
Change in Energy
(Produced work)
Change in Thermodynamic Properties
(Given Energy)
dE = q – PdV
d  independent of the path taken (yoldan bağımsız)
  dependent of the path taken (yola bağımlı)
If we heat up a system the given energy is not stored in the form of heat energy. It cause
increase in internal energy, e.g., increase atomic motions, therefore temperature increases .
1. Law Thermodynamics
dE = q – PdV
‘the change of a body inside an adiabatic
system, from a given initial state to a given final
state, involves the same amount of work by
whatever means the process is carried out’
‘Energy cannot be created, nor destroyed’
energy can change forms
E = U + KE + PE
E=U
dE = dU = q – PdV
Thermodynamic properties depend on :
Temperature (T), Pressure (P), and Volume (V)
T = f(P,V)
E = f(P,V)
𝑑𝐸 =
δ𝐸
δ𝑃
δ𝐸
𝑑𝑃 +
δ𝑉
𝑉
P = f(T,V)
E = f(T,V)
V = f(T,P)
E = f(T,P)
𝑑𝑉
𝑑𝐸 =
𝑃
𝑑𝐸 =
δ𝐸
δ𝑇
δ𝐸
𝑑𝑇 +
δ𝑉
𝑉
𝑑𝑉
𝑇
δ𝐸
δ𝑇
δ𝐸
𝑑𝑇 +
δ𝑃
𝑃
𝑑𝑃
𝑇
In a closed system where E1 and V1
q amount of energy is given
E2 and V2 are reached
dE = dU = q - PdV
E = E2 – E1 = qp – P (V2-V1)
(E2 + PV2) – (E1 + PV1) = qp
H2
H = E + PV
Enthalpy
H1
H2 – H1 = qp
H = qp
independent of the path
dependent of the path
Units
• We use SI units!
• Calorie, the quantity of heat required to raise
the temperature of 1 gram of water from
14.5°C to 15.5°C. Now, we use Joule as energy
unit, 1 cal = 4.18 Joule.
• Temperature unit is Kelvin (K).
• Gas constant R = 8.314 J/mol∙K
Heat Capacity
Heat capacity (C) of a system is the ratio of the
heat added to or withdrawn from the system to
resultant change in the temperature of the
system. Heat capacity at constant volume is Cv
and at constant pressure is Cp.
δ𝑞
𝐶=
𝑑𝑇
(δq)p = (dH)p
𝐶𝑝 =
δ𝑞
𝑑𝑇
δ𝑞
𝐶𝑝 =
𝑑𝑇
δ𝑞
𝐶𝑉 =
𝑑𝑇
𝑃
=
𝑃
𝑑𝐻
𝑑𝑇
𝑃
𝑉
Heat Capacity
δ𝑞
𝐶𝑝 =
𝑑𝑇
𝐻2
𝑑𝐻
𝐻1
=
=
𝑃
𝑑𝐻
𝑑𝑇
𝑇2
𝐶
𝑇1 𝑝
𝐻 = 𝐻2 − 𝐻1 =
𝑃
𝑑𝑇
𝑇2
𝐶
𝑇1 𝑝
𝑑𝑇
Kirchhoff’s Equation
Required energy to increase temperature
Cp = a + b T + cT -2
Heat Capacity
• If there is a phase transition, e.g., melting of a
metal, crystallographic (polymorphic)
transition, then transition enthalpy should be
included, like you did it at high school for
melting latent energy (gizli ısı) for ice.
• To indicate standart conditions ° sign is used.
It is 1 atm and 25°C.
Heat Capacity
Cp = a + b T + c T -2
Cp(A) = 10.5 + 3.4∙ 10-3 T + 5.6∙105 T -2
Material
A
a
b∙103
c∙10-5
Range (K)
10.5
3.4
5.6
200-2500
Heat Capacity
𝐻 = 𝐻2 − 𝐻1 =
𝑇2
𝐶
𝑇1 𝑝
Q = m C T
Q = m.L
Q = mC1 T + m.L + mC2 T
𝑑𝑇
Heat Capacity Values of Selected Materials @25°C
[Cp (J K-1 g-1 or J oC-1 g-1)]
Aluminium
Cp = 0.90
Water
Cp = 4.18
Carbon
Cp = 0.72
Ethanol
Cp= 2.44
Copper
Cp = 0.39
H2SO4
Cp = 1.42
Lead
Cp = 0.13
HCl
Cp = 0.85
Mercury
Cp= 0.14
KOH
Cp= 1.18
What happened if the heat capacity of water were 0.4 instead 4 J/mol K
Heat Capacity at low temperature
Example - 1
1187K
1664K
α-Fe  γ-Fe  -Fe
112 gram of
α-Fe at 300K and γ–Fe at 1200K
Calculate required energy to increase temperatere 100K
for each case.
Cp α-Fe = 37.12 + 6.17∙ 10-3 T
(298 – 1187K)
Cp γ-Fe = 24.48 + 8.45∙ 10-3 T
(1187 – 1664K)
Fe = 56 gr/mol
a) 7855.9 J/112 gr
b) 7008 J/112 gr
Example - 2
at 27°C, take 112 gr Al2O3
In order to increase temperature 100°C,
calculate the required energy.
Cp Al2O3= 117.43 + 10.38∙ 10-3 T - 37.11 ∙ 105 T-2
Answer : 9903.74 J/112 gr
(298 – 1800K)
Hint:
Be careful it is asked from 27°C to 127°C
Actually, it means from 300K to 400 K
Example - 3
Take 1 kg and 1 mol of ZrO2 and calculate
required energy to increase temperature from:
a) RT to 1200K
1450K
α
b) RT to 1600 K
HT = 5900 J/mol
Ttransition = 1450 K
ZrO2 = 123.2 g/mol
Cp α-ZrO2= 69.62 + 7.53∙ 10-3 T - 14.06 ∙ 105 T -2
Cp -ZrO2= 74.48 (1450 – 2800 K)
(298 – 1450K)
a) 521 781 J/kg
b) 819 980 J/kg
Homework
• Plot Temp vs Cp for Al2O3 for the given
temperature:
T = 298, 350, 550, 600, 800, 950, 1100, 1500,
1550, 1650, 1800 K
Cp Al2O3= 117.43 + 10.38∙ 10-3 T - 37.11 ∙ 105 T-2
Use Excel !!!
(298 – 1800K)
What are the advantages of high
specific heat capacity of water?
http://www.tutorvista.com/physics/animations
/advantages-of-high-specific-heat-of-wateranimation
What are the advantages of high
specific heat capacity of water?
http://www.tutorvista.com/physics/animations/
advantages-of-high-specific-heat-of-wateranimation
Hess’s Law
• Hess' law states that
the energy change for any chemical or physical
process is independent of the pathway or
number of steps required to complete the
process provided that the final and initial
reaction conditions are the same. In other
words, an energy change is path independent,
only the initial and final states being of
importance.
(dH)p = (H)p
Basic Definitions
• Heat of reaction (H) (Reaksiyon Isısı)
As a result of a reaction, the enthalpy difference
between initial and final state. Released or
absorbed energy of a chemical reaction.
• H>0 Enthermic reaction, energy required
• H<0 Exothermic reaction, energy release
Basic Definitions
• Enthalpy of Formation (Oluşum, Teşekkül) , it is
a special form of heat of reaction.
• H does not have an absolute value (only change
in H can be measured). Therefore it is
convenient to introduce a convention which
allows the comparison of enthalpy difference.
The convention assigns the value of zero to the
enthalpy of elements in their stable states at
298K. Thus the enthalpy of compound at 298K
is simply the heat of formation of compound
from its elements.
Basic Definitions
𝐻2
𝑑𝐻
𝐻1
=
𝑇2
𝐶
𝑇1 𝑝
𝐻 = 𝐻2 − 𝐻1 =
𝑑𝑇
Kirchhoff’s Equation
𝑇2
𝐶
𝑇1 𝑝
𝑑𝑇
Enthalpy Difference
Enthalpy at
high temperature
𝐻2 = 𝐻1 +
𝑇2
𝐶
𝑇1 𝑝
𝑑𝑇
Enthalpy @ T2
Basic Definitions
A + B = C
T = 298K
Hess’s law
𝐻298 = 𝐻𝐶 298 − (α𝐻𝐴 298+ 𝐻𝐵 298)
Important: This a chemical reaction, due to the reaction there is an Enthalpy Change !
A + B = C
T=T
𝐻𝑇 = 𝐻𝐶 𝑇 − (𝐻𝐴 𝑇+ 𝐻𝐵 𝑇)
Important: This a chemical reaction, due to the reaction there is an Enthalpy Change !
𝐻𝐴 𝑇2 = 𝐻𝐴 𝑇1 +
𝑇2
𝐶
𝑇1 𝑝
𝑑𝑇
Fuels & Combustion
• Combustion (Yanma) is used to describe
exothermic combustion reaction of fuels.
Oxidation reaction such as oxidation of
aluminum is an exothermic reaction but it is
not considered as combustion.
• Conventional fuels can be in solid, liquid or
gas state. The most commonly used fuels are
hydrocarbons.
• Reaction products are water vapour and CO2.
Calorific Value (Kalorifik Güç)
• The heating value or energy value of a
substance, usually a fuel (or food), is the
amount of heat released during the
combustion of a specified amount of it. For
solid and liquids it is 1 kg. For gases 1 m3.
• Reaction is always exothermic but calorific
value is taken positive.
Adiabatic Flame Temperature
(Alev Sıcaklığı)
Fuel298 + Oxidation Agent298 = Reaction ProductsTF
Fuel298 + Oxidation Agent298 = Q + Reaction Products298
Q + Reaction Products298 = Reaction ProductsTF
Adiabatic Flame Temperature
𝑇𝑓
∆𝐶′𝑃(𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) dT
Q298=
298
Combustion at room temperature
Adiabatic Flame Temperature
@ High Temperature
𝑇𝑓
∆𝐶′𝑃(𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) dT
QT =
𝑇
Combustion at high temperature
Flue gas (baca gazı)
𝑇𝑓𝑙𝑢𝑒
Qflue =
298
Always 298K !
Reference point !
∆𝐶′𝑃(𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) dT