1. Chemical Engineering Thermodynamics (CHPE208) Summer 2014-15
Chapter 1
Introduction & Definitions
Chapter 1 – Introduction & Definitions

2. Chapter - 1 Introduction & Definitions
What is Thermodynamics?
System and surroundings
Thermodynamic System Properties
Intensive and extensive properties
Mass, Force, Temperature & Zeroth law of thermodynamics, Pressure, Work & System work, Heat
Dimensions & Units
Chapter 1 – Introduction & Definitions

3. What is Thermodynamics?
Thermodynamics is the branch of physical science which deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and by extension, of the relationships between all forms of energy.
Laws of thermodynamics
Zeroth law (thermodynamic equilibrium and temperature)
First law (conservation of energy [work, and heat])
Second law (Entropy)
Third law (Absolute zero temperature)
Thermodynamics deals with equilibrium states.
Thermodynamic considerations do not establish the rate of chemical or physical processes. Rates depend on driving forces and resistances. Driving forces are thermodynamic variables, but resistances are not.
Thermodynamics does not deal with rate of energy transfer.
Chapter 1 – Introduction & Definitions

4. Chapter 1 – Introduction & Definitions
System & Surroundings
System is defined as a quantity of matter or a region in space chosen for study and application of thermodynamics.
Surroundings: The mass or region outside the system is called its surroundings
Boundary: The real or imaginary surface that separates the system from its surroundings is known as boundary
Types of system: Based on the mass and energy interactions between a system and its surroundings, a systems cane be classified as open, closed or isolated system
Closed system (control mass) consists of fixed mass, and there can be no mass transfer between system and surroundings, but energy can be exchanged between system and surroundings.
Open system (control volume): both energy and mass can be exchanged between a system and its surroundings.
Isolated system: In an isolated system, there can be neither mass nor energy exchange between the system and surroundings
Chapter 1 – Introduction & Definitions

5. Closed System Closed system (also known as a control mass)
Consists of a fixed amount of mass, and no mass can cross the boundary, i.e. no mass can enter or leave the closed system
Energy can cross the boundary
The volume of a closed system does not have to be fixed 5

6. Closed System

7. Isolated System
In an isolated system, even energy is not allowed to cross the boundary NO 7

8. Open System In an Open system (also called control volume)
Both mass and energy can cross the boundary of
a control volume.
Boundaries of a control volume are called a control surface
Control surface can be real or imaginary
A control volume can be fixed in size and shape or it may involve a moving boundary
This involves mass flow such as a compressor, turbine, or nozzle. 8

9. Open System

10. Chapter 1 – Introduction & Definitions
System Properties
Any characteristic of a system is called a property.
Some familiar properties are Pressure (P), Temperature (T), Volume (V), Mass (m)
Density (ρ) is defined as mass per unit volume of substance.
SI units: kg/m3, kg/l, g/cc or g/cm3
Specific volume (ν) is defined as the volume per unit mass ν=V/m = 1/ ρ; SI Units: m3/kg, l/kg, cc/g or cm3/g
Specific gravity (SG) is defined as the ratio of density of a substance to density of some standard substance at specified temperature and pressure
Chapter 1 – Introduction & Definitions 10

11. Chapter 1 – Introduction & Definitions
Types of Properties
Intensive properties are the properties that do not depend on the size (mass) of a system.
Examples: temperature, pressure, and density.
Extensive properties are properties that depend on the size (mass) of a system.
Examples: Mass m, Volume V, and total Energy E.
Specific properties. Some examples of specific properties are specific volume (v = V/m) and specific total energy (e = E/m).
Note: Ratio of any two extensive properties is an intensive property. Example:  = m/V, v = V/m
Chapter 1 – Introduction & Definitions

12. Chapter 1 – Introduction & Definitions
How to differentiate between intensive and extensive properties?
Divide the system into two equal parts with a partition
If each part has the same property value as the original system, the property is intensive
If each part has only half the property value of the original system, the property is extensive
Chapter 1 – Introduction & Definitions

13. Chapter 1 – Introduction & Definitions
Mass
Chapter 1 – Introduction & Definitions

14. Chapter 1 – Introduction & Definitions
Force
Exercise: An astronaut weighs 730 N in Houston, Texas, where the local acceleration of gravity is g = 9.81 m/s2. What are the astronaut’s mass and weight on the moon, where g = 1.67 m/s2?
Chapter 1 – Introduction & Definitions

15. State and Equilibrium1/2
For a system not undergoing any change, a set of properties which can completely describe the system is called as the state of the system.
At a given state, all the properties of a system have fixed values
If the value of one property changes, the state will change
Thermodynamics deals with
equilibrium states.
• In an equilibrium state, there are no unbalanced potentials
(or driving forces) within the system

16. State and Equilibrium2/2
Thermodynamic Equilibrium:
A system is said to be in thermodynamic equilibrium if it maintains thermal, mechanical, phase, and chemical equilibrium.
Thermal Equilibrium: The temperature throughout the
entire system is uniform
Mechanical Equilibrium: The pressure throughout the
Phase Equilibrium: The mass of each phase is in
equilibrium
Chemical Equilibrium: Chemical composition does not
change with time, i.e.no chemical reactions take place 16

17. The State Postulate

18. Processes and Cycles
Process: Any change that a system undergoes from one equilibrium state to
another is called as a process.
Path: Path is the series of states through which a system passes during a process.
How to describe a process completely? To describe a process completely, one should specify the initial and final states of the process as well as the path it follows, and the interaction with surroundings
Cycle: A system is said to have undergone a cycle if it returns to its initial state at the end of the process, and so the initial and final states are identical for a cyclic process.

19. Types of Processes
In most of the processes we study, one property of thermodynamic is held constant, also, the prefix iso- is often used to designate a process for which a particular property remains constant.
isothermal process, is a process during which the temperature T remains constant;
isobaric process is a process during which the pressure P remains constant; and
isochoric (or isometric) process is a process during which the specific volume v remains constant.
Isentropic process: Entropy held constant 19

20. Steady and Unsteady States
Steady state implies no change with time. The term uniform, however, implies no change with location over a specified region.
Unsteady state or transient, the opposite of steady
The steady-flow process:
a process during which a fluid flows through a control volume steadily. That is, the fluid properties can change from point to point within the control volume, but at any fixed point they remain the same during
the entire process (V, m & E), ie not change with time.
Steady-flow Process
Here CV – Control volume 20

21. Temperature and the Zeroth Law of Thermodynamics
A measurement of the overall microscopic kinetic energy
of a body or a system,
fast-moving molecules have high kinetic energy → they
have high temperature.
when an object is in contact with another object that is at a different temperature, heat is transferred from the object
at higher temperature to the one at lower temperature
until both objects attain the same temperature
(ie Thermal Equilibrium).
The equality in Temperature is the only requirement for thermal equilibrium
Chapter 1 – Introduction & Definitions

22. Temperature and the Zeroth Law of Thermodynamics
If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other
If the third body is a thermometer and it is in thermal equilibrium with two different bodies, then the two bodies must also be in equilibrium and at the same temperature
Chapter 1 – Introduction & Definitions 22

23. Chapter 1 – Introduction & Definitions

24. Chapter 1 – Introduction & Definitions
Pressure
Example: At K (27C) the reading on a manometer filled with mercury is 60.5 cm.
The local acceleration of gravity is m/s2. To what pressure does this height of mercury correspond?
Chapter 1 – Introduction & Definitions

25. Chapter 1 – Introduction & Definitions
Work
Chapter 1 – Introduction & Definitions

26. Chapter 1 – Introduction & Definitions
System work
When work is done by a thermodynamic system, it is usually a gas that is doing the work. The work done by a gas at constant pressure is:
For non-constant pressure, the work can be visualized as the area under the pressure-volume curve which represents the process taking place. The more general expression for work done is:
System work is a major focus in the discussion of heat engines.
Chapter 1 – Introduction & Definitions

27. Chapter 1 – Introduction & Definitions
Energy - 1
Since the definition of velocity is u = dl/dt, the expression for work becomes,:
This equation may now be integrated for a finite change in velocity from u1 to u2:
Chapter 1 – Introduction & Definitions

28. Kinetic Energy - Exercise
Problem: An automobile having a mass of 1250 kg is travelling at 40 m/s. What is its kinetic energy? How much work must be done to ring it to a stop? Answer: Given data: m = 1250 kg; velocity, v = 40 m/s A work equivalent to the kinetic energy must be done to stop the automobile, Work = 1 MJ
Chapter 1 – Introduction & Definitions

29. Chapter 1 – Introduction & Definitions
Energy - 2
Exercise: Verify that the SI unit of kinetic and potential energy is the joule
Chapter 1 – Introduction & Definitions

30. Chapter 1 – Introduction & Definitions
Heat
A hot object brought in contact with a cold object becomes cooler, whereas the cold object becomes warmer because heat (Q) is transferred from the hot object to the cold one.
Heat always flows from higher temperature to a lower one, and when there is no temperature difference there is no net transfer of heat.
Temperature difference is called as the driving force for the heat transfer. The rate of heat transfer from one body to another is proportional to the temperature difference between the two bodies.
In thermodynamic sense, heat is never regarded being stored within a body. Heat exists only as energy in transit from one body to another.
When heat is added to system, it is stored not as heat but as kinetic and potential energy of the atoms and molecules making up the system.
Chapter 1 – Introduction & Definitions

31. Dimensions and Units - 1 Primary Dimension Symbol SI unit
mass
m (sometimes M)
kg (kilogram)
length
L (sometimes l)
m (meter)
time
t (sometimes T)
s (second)
temperature
T (sometimes q )
K (Kelvin)
electric current
I (sometimes i)
A (ampere)
amount of light  (luminous intensity)
C (sometimes I)
c (candela)
amount of matter
n or N (sometimes )
mol (mole)
Secondary Dimension
SI Unit
Force F
N (Newton)
Acceleration a
m/s2
Pressure
P or P
N/m2, Pa
Energy E
J, N.m
Power P
W (J/s)
Chapter 1 – Introduction & Definitions

32. Chapter 1 – Introduction & Definitions
Dimensions and Units - 2
Chapter 1 – Introduction & Definitions