BASIC CONCEPTS OF
THERMODYNAMICS
Chemical Thermodynamics (A)
Chemistry and Energy Relations
Lecture Notes 07
Chemistry for Engineers
BASIC CONCEPTS OF THERMODYNAMICS
INTRODUCTION
THERMODYNAMICS is the study of the interrelation of various forms of energy. It
came from the Greek words “therme” (heat) and “dy’namis” (power).
CHEMICAL THERMODYNAMICS is the study of the interrelation between heat
and work with chemical reactions or with physical changes of states within the
scope of the laws of thermodynamics.
CHEMICAL ENERGY is the energy stored in all substances which appears when
the substances undergo transformation.
BASIC CONCEPTS OF THERMODYNAMICS
THERMODYNAMIC SYSTEMS
SYSTEM – is defined as any part of the universe that is chosen for a study and is
confined in an inert container, which can either be real or imaginary, to separate
it from the rest of the universe
SORROUNDINGS – is the rest of the universe that isn’t defined as the system
boundary
surroundings
system
BASIC CONCEPTS OF THERMODYNAMICS
CLASSIFICATIONS OF SYSTEM
1. ISOLATED – a system that is not capable of exchanging neither matter nor
energy with the rest of the universe
2. CLOSED – a system that is capable of exchanging only energy but not matter
with the surroundings
3. OPEN – a system that is capable of exchanging both matter and energy across
the boundary
BASIC CONCEPTS OF THERMODYNAMICS
PHASES OF A SYSTEM
PHASE – is defined as a homogeneous, physically distinct and mechanically
separable portion of a system
HOMOGENEOUS SYSTEM – a system that consists of only one phase
HETEROGENEOUS SYSTEM – a system consisting of two or more phases
BASIC CONCEPTS OF THERMODYNAMICS
PROPERTIES OF A SYSTEM
PROPERTY – a characteristic which can be quantitatively evaluated or a
characteristic quality of the system which depends on the final system. Examples
are pressure, temperature, energy
GENERAL CLASSES OF THERMODYNAMIC PROPERTIES
1. Extensive properties – those that are dependent on the mass of the system
2. Intensive property – those that are independent on the mass of the system
BASIC CONCEPTS OF THERMODYNAMICS
THERMODYNAMIC STATES AND PROCESSES
THERMODYNAMIC PARAMETERS – are measurable physical characteristics of a system that enable us to define
the system itself (composition, volume, temperature, pressure)
STATE OF A SYSTEM – is the system’s condition described or measured by a set of thermodynamic variables. It
changes when one or more of its thermodynamic variables undergo(es) change(s)
STATE FUNCTION – a thermodynamic property which depends only on the state of the system but not on the
paths followed by the system during the change. Examples are changes in internal energy, enthalpy, entropy and
free energy.
EQUILIBRIUM STATE – a system with fixed composition, a uniform temperature of the system and with its
surroundings, and with no unbalanced force within the system and the system and its surroundings.
PATH is a locus of series of states through which a system passes between initial and final states.
PROCESS is the transformation of a thermodynamic system from one thermodynamic state to another
BASIC CONCEPTS OF THERMODYNAMICS
TYPES OF PROCESSES
Isothermal – occurs when the change of the system occurred at constant temperature
Isobaric – occurs when the change of the system is observed but the operation was
carried out at constant pressure
Isochoric – occurs when the change of the system took place under a constant volume
Adiabatic – occurs when the change in the system occurred without an exchange of
heat with the surroundings but the temperature of the system changes.
Isentropic – the entropy remains constant during the process
Isenthalpic – the enthalpy remains constant during the process
BASIC CONCEPTS OF THERMODYNAMICS
CLASSIFICATIONS OF PROCESSES
Non-flow process – a process undergone by fluid in a closed system
Flow process – a process undergone by a fluid in an open system
Reversible process – a process in which the energy change in every step of the process
can be reversed in direction by an infinitesimal change in any of the variables acting on
the system. A process can be made reversible by performing the change very slowly
with no friction and no finite temperature differences.
Irreversible process – a process in which the system and the surrounding after
undergoing changes cannot get back to their initial state and tend to proceed to a
different direction but cannot proceed to the reverse direction
BASIC CONCEPTS OF THERMODYNAMICS
DIMENSIONS OF UNITS
QUANTITY
SI UNIT
ENGLISH UNIT
Length
meters (m)
foot (ft)
Mass
kilogram (kg)
pound mass (lbm)
Time
second (s)
second (s)
Temperature
Kelvin (K)
Rankine (R)
Volume
cubic meter (m3)
cubic feet (ft3)
Pressure
Pascal (Pa)
pound per square inch (psi)
Force
Newton (N)
pound force (lbf)
Energy
Joules (J)
foot-pound force (ft-lbf)
BASIC CONCEPTS OF THERMODYNAMICS
COMMON CONVERSION FACTORS
BASIC CONCEPTS OF THERMODYNAMICS
COMMON CONVERSION FACTORS
BASIC CONCEPTS OF THERMODYNAMICS
COMMON CONVERSION FACTORS
BASIC CONCEPTS OF THERMODYNAMICS
BASIC CONCEPTS OF THERMODYNAMICS
DENSITY, SPECIFIC VOLUME AND SPECIFIC WEIGHT
Density of a substance is the ratio of the mass to the volume of the substance
Specific volume of a substance is the ratio of the volume to the mass of the substance
Specific weight of a substance is the ratio of the weight to the volume of a substance
Specific gravity (relative density) of a liquid is the ratio of density of the liquid to the
density of water at a specified temperature
Specific gravity (relative density) of a gas is the ratio of the density of air to the density
of water at a specified temperature and pressure
BASIC CONCEPTS OF THERMODYNAMICS
TEMPERATURE
Temperature is the measure of the coldness or warmth of a substance
Absolute temperature is the temperature measured using a scale beginning at
zero, with that zero being the coldest theoretically attainable in nature.
Boiling point – the state wherein the liquid and the gaseous phases of a
substance is at equilibrium
Melting point – the state wherein the solid and the liquid phases of a substance
is at equilibrium
Triple point – the state wherein all three phases (solid, liquid and gas) of a
substance coexist simultaneously (Triple point of water is 0.01°C)
BASIC CONCEPTS OF THERMODYNAMICS
TEMPERATURE: the measure of the coldness or warmth of a substance
BASIC CONCEPTS OF THERMODYNAMICS
PRESSURE
Pabsolute = Pgauge + Patmospheric
BASIC CONCEPTS OF THERMODYNAMICS
ENERGY
ENERGY is defined as the capacity or ability to do work.
POTENTIAL ENERGY of a system is a result to its elevation in a gravitational field.
PE = mgh
KINETIC ENERGY of a system is a result of motion relative to some reference
KE = ½ mv2
INTERNAL ENERGY of a system is the energy stored within the body resulting from the kinetic and
potential energy in molecules.
U = PE + KE
BASIC CONCEPTS OF THERMODYNAMICS
ENERGY
MECHANICAL ENERGY is a form of energy that can be converted directly and
completely into mechanical work by an ideal mechanical device such as an ideal
pump or turbine.
ENTHALPY of a system is the energy that is equivalent to the sum of the internal
energy of the system and the product of the pressure and the volume
H = U + PV
HEAT is a form of energy that flows between two systems by virtue of a
temperature difference between them.
BASIC CONCEPTS OF THERMODYNAMICS
WORK
WORK is the energy transfer associated with force acting through a distance
TYPES OF WORK
1. Electrical work is the work done on a charged particle by an electric field
Welectrical = VI∆t
2. Mechanical work is the amount of energy transferred by a force or the work done by
a system
W = Fd
BASIC CONCEPTS OF THERMODYNAMICS
3. Moving boundary work occurs when the mass of the substance contained within the
system boundary causes force to act on the boundary surface and make it move
W = p∫dV
4. Gravitational work is the work done against the force of gravity
W= mg
5. Acceleration work is the work associated with change in the velocity of a system
W = 1/2m (v22 -v12)
6. Shaft work is the work done with energy transmission with a rotating shaft
7. Spring work is the work done by a spring as a result of the application of force to it
BASIC CONCEPTS OF THERMODYNAMICS
SAMPLE PROBLEMS
1. Carry out the following conversions of energy units: (a) 14.3 BTU into cal,
(b) 1.4 x105 cal into joules, (c) 31.6 mJ into BTU
2. Make the following conversions: (a) 72°F to °C; (b) 216°C to °F; (c) 233°C to K;
(d) 315K to °F; (e) 0K to °F
3. Suppose you decide to define your own temperature scale using the freezing
point (13°C) and boiling point (360°C) of oleic acid, the main component of
olive oil. If you set the freezing point of oleic acid as 0°O and the boiling point
as 100°O, what is the freezing point and boiling point of water on this new
scale?
BASIC CONCEPTS OF THERMODYNAMICS
SAMPLE PROBLEMS
4. The density of air at ordinary atmospheric pressure and 25°C is 1.19 g/L.
What is the mass, in kilograms, of the air in a room that measures 14.5 ft x
16.5 ft x 8.0 ft.
5. (a) A sample of tetrachloroethylene, a liquid used in dry cleaning that is being
phased out because of its potential to cause cancer, has a mass of 40.55g and
a volume of 25.0mL at 25°C. What is its density at this temperature?
(b) Carbon dioxide is a gas at room temperature and pressure. However,
carbon dioxide can be put under pressure to become supercritical fluid that is
much safer dry-cleaning agent than tetrachloroethylene. At a certain
pressure, the density of supercritical CO2 is 0.469 g/cm3. What is the mass of
a 25.0mL sample of supercritical CO2 at this pressure?
BASIC CONCEPTS OF THERMODYNAMICS
SAMPLE PROBLEMS
6. An astronaut weighs 739N in Houston, Texas, where the local acceleration of gravity
is g = 9.793 m/s2. What are the astronaut’s mass and weight in the moon where g =
1.67 m/s2?
7. A dead-weight gauge with a 1-cm diameter piston is used to measure pressures
very accurately. In a particular instance, a mass of 6.14kg (including piston and pan)
brings it into balance. If the local acceleration of gravity is 9.82 m/s2, what is the
gauge pressure being measured? If the barometric pressure is 748 torr, what is the
absolute pressure?
8. At 27°C, the reading on a manometer filled with mercury is 60.5 cm. The local
acceleration of gravity is 9.784 m/s2. To what pressure does this height of mercury
correspond? Express answer in bar. Density of mercury at 27°C is 13.53g/cm3.
BASIC CONCEPTS OF THERMODYNAMICS
SAMPLE PROBLEMS
9. A fluid has a density of 920 kg/m3. What is the specific gravity of the fluid?
10. A condenser vacuum gauge read 580 mmHg when the barometer reads 760
mmHg. Determine the absolute condenser pressure in bars.
11. The initial pressure and volume in a piston-cylinder arrangement are 300 kPa
and 2m3, respectively. Energy is added to the system and the piston is
withdrawn in such a way that the quantity PV remains constant. If the final
pressure is 100 kPa, find the work done by the gas on the piston.
BASIC CONCEPTS OF THERMODYNAMICS
REFERENCES
Brown, T.L., Lemay Jr., H.E., Bursten, B.E., Murphy, C.J., and Woodward, P.M. (2012) Chemistry: The
Central Science, 12th Ed., USA: Pearson Education, Inc.
Brown, L.S. and Holme, T.A. (2011) Chemistry for Engineering Students, 2nd Edition, USA, Brooks/Cole,
Cengage Learning
Chang, R. (2010) Chemistry, 10th Ed., New York, McGraw Hill
Maron, S.H and Lando, J.B. (1974) Fundamentals of Physical Chemistry. Macmillan Publishing Co. Inc.
New York, USa
Smith, J.M., Van Ness, H.C., Abbot, M.M. (1996) Introduction to Chemical Engineering Thermodynamics,
5th Ed., McGraw Hill International Editions, Chemical Engineering Series, Singapore
Tordillo, J. (2019) Simplified Engineering Thermodynamics For Thermodynamics 1 and 2, Tordillo
Publising, Cebu City, Philippines