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Introduction to Chemical Engineering
Thermodynamics
Chapter 2
1KFUPM Housam Binous CHE 303
2KFUPM Housam Binous CHE 303
Internal energy
It does not include energy due to macroscopic position ormovement
Addition of heat increases molecular activity and hence internalenergy
First Law of Thermodynamics
KFUPM Housam Binous CHE 303 3
Although energy assumes many forms, the total quantity
of energy is constant, and when energy disappears in one
form it appears simultaneously in other forms
KFUPM Housam Binous CHE 303 4
potential, kinetic and internal energy are
stored with matter
heat and work are energy in transit across
the boundary separating system and
surroundings
KFUPM Housam Binous CHE 303 5
Energy balance for closed system
no energy associated with matter is transportedacross the boundary
All energy exchange appears as heat and work
closed system
KFUPM Housam Binous CHE 303 6
Specific and molar internal energy are intensive
SI Units are Joule/kg and Joule/mole
No absolute value of the internal energy
But only changes in this property can be calculated
KFUPM Housam Binous CHE 303 7
Depend only on present conditions and not on how they
were reached
State functions
Differential of a state function = infinitesimal change
Differentials of heat and work = infinitesimal amounts
KFUPM Housam Binous CHE 303 8
W+Q is the same for all paths but the amount of
heat or work exchanged is dependent on the process
KFUPM Housam Binous CHE 303 9
Equilibrium
No change and no driving force or tendency for change
In a system not at equilibrium with an appreciable driving force:
change will not occur if the resistance to change is very large
KFUPM Housam Binous CHE 303 10
The phase rule (Gibbs, 1875)
Number of phases
Number of chemical species
KFUPM Housam Binous CHE 303 11
Reversible ProcessesFrictionless
Differentially removed from equilibrium
Traverses succession of equilibrium states
Driven by force imbalances which are differential inmagnitude
Can be reversed at any point by differential change inexternal conditions
When reversed it retraces the forward path and restores theinitial state of the system and the surroundings
KFUPM Housam Binous CHE 303 12
KFUPM Housam Binous CHE 303 13
KFUPM Housam Binous CHE 303 14
Reversible processes are said mechanically reversible
KFUPM Housam Binous CHE 303 15
Constant-volume process
Mechanically reversible closed-system process:
If in addition, constant-volume process:
KFUPM Housam Binous CHE 303 16
Constant-pressure process
Enthalpy
KFUPM Housam Binous CHE 303 17
Heat Capacity at Constant Volume
Mechanically reversible closed-system contant-volume process:
KFUPM Housam Binous CHE 303 18
Heat Capacity at Constant Pressure
Mechanically reversible closed-system contant-pressure process:
KFUPM Housam Binous CHE 303 19
Mass Balance for Open Systems
KFUPM Housam Binous CHE 303 20
Assume: (1) steady-state
(2) single entrance and single exit stream
KFUPM Housam Binous CHE 303 21
The General Energy Balance
KFUPM Housam Binous CHE 303 22
Shaft work
Expansion/ contraction work
Stirring work
KFUPM Housam Binous CHE 303 23
Energy Balance for steady-state processes
Steady-state: no changes with time
Thus consider only shaft work
KFUPM Housam Binous CHE 303 24
Flow calorimeter for enthalpy measurements
liquid water at 0°C