University of Mines and Technology

Chemical Thermodynamics
( RP 263)
CHAPTER 1
Dr Benjamin Edem Meteku
Department of Chemical & Petrochemical Engineering
bemeteku@umat.edu.gh
February 2024
 Course Objectives
❖ To help students understand the standard enthalpy of
formation and its temperature dependence (Hess's law) based
on the first law of thermodynamics.
❖ To help students derive important thermodynamic relations.
❖ To help students perform numerical calculations
involving thermodynamic variables.
❖ To help students apply thermodynamic principles to
analyze practical problems.
❖ To explain various chemo-thermal phenomena by
understanding Gibbs energy and chemical potential.
 Course Description
❖ This course describes the fundamentals of thermodynamics based on
the first and the second laws of thermodynamics and demonstrates
how the newly introduced concepts such as entropy, Gibbs energy, and
chemical potential can explain many thermal phenomena.
❖ Among various thermodynamic topics in many fields, this course
focuses on familiar chemical phenomena (e.g., Hess's law, calculation
of enthalpy of a reaction using Hess’s law. Explain bond enthalpy and
solve bond enthalpy problems etc.)
❖ As one of the science and engineering basic courses required for
Engineering disciplines, this course provides essential contents of
chemical thermodynamics using some fundamental principles in
Chemistry.
 Course Content
❖ Fundamental Concepts in Thermodynamics
❖ First Law of Thermodynamics
❖ Laws of Thermochemistry
❖ Second Law of Thermodynamics
 Mode of Delivery
❖ Lectures

❖Tutorials

❖Group Work

❖Assignment.
 Assessment of Students
❖ Attendance [10%]

❖ Continuous Assessment [30%]

- Assignments
- Quizzes

❖ End of Semester Exams [60%]

 Reading Materials
❖ Dahm, D. and Visco, D. P. (2014), Fundamentals of Chemical Engineering Thermodynamics,
Cengage Learning Publishers, Boston, United States, 1st Edition, 700 pp
❖ Elliott, J. R and Lira, C. T (2012), Introduction to Chemical Engineering Thermodynamics,
Prentice Hall, New Jersey, United States, 2nd Edition 912 pp
❖ Koretsky, M. D. (2012), Engineering and Chemical Thermodynamics, Wile Publisher, New York
City, United States, 2nd Edition, 704 pp
❖ Smith, J. M., Van Ness, H. C., Abbott, M. M. and Swihart, M. T. (2017), Introduction to Chemical
Engineering Thermodynamics, McGraw-Hill Education; New York, United States, 8th Edition, 768
 INTRODUCTION
❖ The branch of science which deals with the study of
different forms of energy and the quantitative relationship
between them is as thermodynamics.
❖ However, when we confine our study to chemical changes
and chemical substances(species) only, then that branch of
thermodynamics is known as chemical thermodynamics.
❖ When a chemical reaction occurs, it is accompanied by an
energy change which may take any of several different forms.
- For example, the energy change involved in the
combustion of fuels like kerosene, coal, wood, natural gas,
etc., takes the form of heat and light.
 INTRODUCTION
❖ Electrical energy is obtained from chemical reactions in
batteries (a battery is a device that stores chemical energy and
converts it to electrical energy).
❖ The formation of Glucose ( C6H12O6 )by the process of
photosynthesis requires the absorption of light energy from
the sun.
❖ In summary, the energy change that accompanies a
chemical reaction can take different forms.
 INTRODUCTION – Historical Perspective
❖Benjamin Thompson, in 1798, proposed a link between
work and heat generated from observing the boring of
cannons
❖Nicolas Carnot, in 1824, first proposed the concept of
reversibility
❖James Joule (a brewmaster), between 1840-1849 measured
rising temperature from mechanical stirring – quantifying the
relation between work and heat
❖The term ‘thermodynamics’ was coined by Kelvin in 1849
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
System, Surroundings and Boundary
❖ System: A system is the part of the physical universe which is
under study.
❖ Surroundings: The rest of the physical universe or environment
around the system.
Hence, the surrounding means all other things which can
interact with the system.
❖ Boundary: Any real or imaginary surface separating the system
from the surroundings.
Thus,
UNIVERSE = SYSTEM + SURROUNDINGS
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
System, Surroundings and Boundary

Thermodynamic System Water Contained in a Beaker Constitutes a System

FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Thermodynamic Systems
Depending on how a system interacts with the surroundings, there are three
(3) categories of systems namely; Closed, Open and Isolated systems.

❖ Open System: An Open System is a system which can exchange both

matter and energy (heat or work) with the surroundings
Example, Hot water contained in an open beaker.
❖ Closed System: A Closed System (also known as control mass) is a system
which CANNOT exchange matter with the surrounding BUT can exchange
energy (heat or work)
❖ Isolated System: An Isolated system is a system which can exchange
neither matter nor energy with the surrounding. If the boundary is closed and
insulated, no interaction is possible with the surrounding. Example, Hot or
cold water contained in a thermos flask.
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Thermodynamic Systems

The Three Types of Thermodynamic Systems

FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Thermodynamic Systems
Preamble
A hot tea (let us call it a system)kept in a stoppered thermos flask
remains hot for a couple of hours.
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS

Types of Thermodynamic Systems

❖If this flask is made of perfect insulating material, then there
would be no exchange of matter or energy between the system and
the surroundings. Hence we have an Isolated System.

❖ If we keep hot tea in a stoppered glass or stainless-steel flask, it

will not remain hot after some time. Here energy is lost to the
surroundings through the steel walls, but due to stopper, the matter
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Thermodynamic Systems

Plants, animals, human beings are all examples of open systems, because they
continuously exchange matter (food, etc) and energy with the surroundings.
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
State of a System
❖The State of a system refers to the condition of the system

❖The thermodynamic State of a System is defined by specifying

values for a set of measurable properties sufficient to determine all
other properties.

❖ For fluid systems, the fundamental properties which determine

the state of the system include Pressure, Volume and Temperature
(P,V,T)

❖ The measurable properties of a thermodymic system are called

State Variables or State functions
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
State of a System

❖ A State Function is a property whose value does not

depend on the path taken to reach that specific value

❖ In contrast however, Path Functions are functions that

depend on the path taken to reach that specific value. Eg.
Heat (q) and work (w)

❖ Steady state is when none of the properties of a system

changes with time
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
State of a System
❖ When the state of a system changes, the change depends only on
the initial and the final state (second state) of the system and NOT
the path taken

Change of State from Initial State to Final State through 3 paths: I, II and III
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
State of a System
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
❖ A thermodynamic property is a characteristic of a
system and it is used to specify the condition or state of a
system

❖Examples include; pressure, temperature, volume, mass

 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
❖ Several thermodynamic properties are typically used to describe the
interactions between a system and its surroundings:
- mass m
- pressure p
- temperature T
- volume V and specific volume v
- internal energy U and specific internal energy u
- enthalpy H and specific enthalpy h
- entropy S and specific entropy s
❖These measurable properties of a system, state functions (state variables)
may be divided into two namely; intensive and extensive properties, based
on their dependence on mass.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
❖ Extensive property is a thermodynamic property that
depends on the size of the system or amount of material
(mass dependent).

Properties such as: mass, volume, internal energy,

enthalpy, entropy, mole, and Gibbs’ free energy are all
extensive properties.
Their values change accordingly as the size of the system
changes (Depends on the quantity of matter in a system)
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
❖ Intensive property is a thermodynamic property that is NOT
dependent on size of the system or amount of material (mass
independent).
Properties such as age, colour, pressure, temperature, viscosity,
density, surface tension, refractive index, specific internal energy,
specific enthalpy and specific entropy.
Their values do not change when the sample size of the system changes
(Does not depend on quantity of matter).
NB
All specific properties are intensive properties because they refer to
the corresponding extensive property per unit mass.
E.g. specific volume
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
Example of Intensive Property

If the overall temperature of a glass of water (our system) is 20ºC,

then any drop of water in that glass has a temperature of 20ºC.

Similarly if the concentration of salt, NaCl, in the glass of water is

0.1 mole/litre, then any drop of water from the glass also has a salt
concentration of 0.1 mole/litre.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
Summary of Properties

❖Extensive properties ?
depend on the size of the system and hence the mass of the system. Examples
include mass, volume, and total energy.

❖Intensive properties ?
are independent of the size of the system. They include pressure and
temperature.

❖A specific property (denoted by lower case letters) refers to an extensive

property per unit mass. eg. v = V/m.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
Practice Problems
1. Is volume an extensive or intensive property?
2. Is density an extensive or intensive property?
3. The mass of a system is 2kg. If the internal energy of the
system is U, what is
(a) the specific internal energy of the system
(b) Is the calculated property in (a) intensive or extensive
4. What is the relation between an extensive property B and
its corresponding intensive property b
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Properties of a System
Practice Problems
Answers

1. extensive
2. intensive
3. a) U/2
b) intensive
4. B = m*b )
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
❖A System may change from one state to another state through a
Process.
A change from one state to another is a process.
❖These processes involve the change of conditions such as
temperature, pressure, volume.

❖ For example,
Suppose we want to raise the temperature of a system. We may do it
by heating it. Here, heating is the process. The method of bringing
about a change in state is called process.
The following are the common thermodynamic processes:
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
1. Isothermal Process
Processes in which the temperature remains constant or fixed. This is often
achieved by placing the system in a thermostat ( constant temperature bath).
For an Isothermal process,
dT = 0
For example,
Ice melts at 273 K and 1 atm pressure. The temperature does not change as
long as the process of melting goes on.
When the temperature of the system remains constant during various
operations, then the process is said to be isothermal. This is attained either by
removing heat from the system or by supplying heat to the system.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
2. Adiabatic Process
Processes in which no heat flows into or out of the system. In other words, no
heat transfer occurs between a system and its surrounding.
Adiabatic conditions can be approached by carrying the process in an insulated
container such as ‘thermos’ bottle/flask. High vacuum and highly polished
surfaces help to achieve thermal insulation.
For an adiabatic process,
dq = 0
For example
If an acid is mixed with a base in a closed thermos flask, the heat evolved is
retained by the system. Such processes are known as adiabatic processes
because the thermos flask does not allow exchange of heat between the system
and the surroundings.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
3. Isobaric Process
Processes which take place at constant pressure or the pressure remains
constant. They are also referred to as Isopiestic
For an Isobaric process,

dp = 0
For example,
Heating of water to its boiling point and its vaporisation take place at the same
atmospheric pressure. These changes are therefore designated as isobaric
processes and are said to take place isobarically.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
4. Isochoric Process
Processes in which the volume remains constant.
For an Isochoric process,
dV = 0
For example,
The heating of a substance in a non-expanding chamber is an example of
isochoric process.

5. Isentropic process
Processes in which the entropy remains constant.
For an Isentropic process,
dS = 0
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
6. Cyclic Process
When a system in a given state goes through a number of different
processes and finally returns to its initial state, the overall process is
called a cycle or cyclic process.

In other words, a thermodynamic cycle or cyclic process is a

sequence of processes that begins and ends at the same state.
For a Cyclic process,
dE = 0 and dH = 0
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Types of Processes
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Reversible and Irreversible Processes
Reversible Processes
A thermodynamic reversible process is one that takes place
infinitesimally slowly and its direction at any point can be reversed
by an infinitesimal change in the state of the system.

❖ In a reversible process, the initial and the final states are

connected through a succession of equilibrium states. All changes
occurring in any part of the process are exactly reversed when it is
carried out in the opposite direction.

❖ Thus both the systems and its surroundings must be restored

exactly to their original state, when the process has been performed
and then reversed.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Reversible and Irreversible Processes
Preamble for Concept
Imagine a liquid in equilibrium with its vapor in a cylinder closed by a
frictionless piston, and placed in a constant temperature bath as shown below:

❖ If the external pressure on the piston

is increased by an infinitesimally
small amount, the vapors will
condense, but the condensation will
occur so slowly that the heat evolved
will be taken up by the temperature
bath.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Reversible and Irreversible Processes
Preamble for Concept
❖ The temperature of the system will not rise, and the pressure above
this liquid will remain constant. Although condensation of the vapor is
taking place, the system at every instant is in the state of equilibrium. If
the external pressure is made just smaller than the vapor pressure, the
liquid will vaporize extremely slowly, and again temperature and
pressure will remain constant.

❖ In the above example rapid evaporation or condensation by the sudden

decrease or increase of the external pressure, will lead to non-
uniformity in temperature and pressure within the system and the
equilibrium will be disturbed. Such processes are known as
irreversible processes.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Reversible and Irreversible Processes
Irreversible Processes
A thermodynamic irreversible process is one that when the process
is initiated, no infinitesimal change in external conditions can
reverse it.
❖ Factors that cause a process to be
irreversible are called irreversibilities
and include: Friction, mixing of two
fluids, electric resistance, chemical
reactions etc.
❖ All real processes and all spontaneous
Processes are irreversible. Eg rusting
FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Reversible and Irreversible Processes
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Exothermic & Endothermic Reactions
Exothermic Reactions
❖ Add a few cm3 of dilute HCl in a test tube containing a few pieces of
granulated zinc and observe the evolution of a gas. Feel the test tube. It
would be hot.
❖ You must have also observed that when some water is added to quick
lime to prepare white wash, a lot of heat is evolved
❖ When a fuel like cooking gas or coal is burnt in air, heat is evolved
besides light
❖Many chemical reactions such as the above, lead to release of energy
(heat) to the surroundings. We call these type of reactions as
exothermic reactions
❖Exothermic reactions are those reactions which proceed with the
evolution of heat or reactions in which chemical energy is released
as heat energy.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Exothermic & Endothermic Reactions
Endothermic Reactions
❖ Add a small amount of solid ammonium chloride in a test tube
half-filled with water. Shake and feel the test tube. It will feel cold.
❖ Similarly repeat this experiment with potassium nitrate and feel
the test tube, it will feel cold
❖ Mix barium hydroxide with ammonium chloride in small
quantities in water taken in a test tube. Feel the test tube. It will be
cold.
❖ In all the above processes we see that heat is absorbed by the
system from the surroundings. Such reactions are called
endothermic reactions.
❖Endothermic reactions are those reactions which proceed with
the absorption of heat from the surroundings.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
❖ These are balanced stoichiometric chemical equations in which energy(heat)
changes and the states of the reactants and products are specified.

❖ Rules/Conventions for writing Thermochemical Equations

1. The Physical state of the reacting species or products be it solid, liquid or gas
are denoted by symbols in bracket beside the chemical formulae
solid – (s)
liquid – (l)
gas – (g)
2. The amount of heat evolved or absorbed is denoted by the symbol ΔH and is
written after the equation followed by semicolon (;)
ΔH = (- ) = Exothermic
ΔH = (+) = Endothermic
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
❖ Rules/Conventions for writing Thermochemical Equations
3. In case of elements which exhibit allotropy, (the existence of two or
more different physical forms of a chemical element) the name of allotropic
modification is mentioned. For example,
C (graphite), C (diamond), etc

4. The substances in aqueous solutions are specified using the symbol (aq).
For example NaCl (aq) stands for an aqueous solution of sodium chloride.

5. Thermochemical equations may be balanced even by using fractional

coefficients, if so required. The coefficients of the substances of the chemical
equation indicate the number of moles of each substance involved in the
reaction and the ∆H values given correspond to these quantities of substances.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
❖ Example for Exothermic reaction

CH4 (g) + 2O2 (g) CO2 (g) + 2H2 O (l); ∆H= – 891 kJ

❖ Example for Endothermic reaction

H2 (g) + I2 (g) 2HI (g); ∆H= 52.2 kJ

 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
❖ In case the coefficients are multiplied or divided by a factor, ∆H value must also be
multiplied or divided by the same factor. In such cases, the ∆H value will depend upon the
coefficients. For example, in equation

H2 (g) + O2 (g) →H2O (g); ∆H= – 242 kJ

❖ If coefficients are multiplied by 2, we would write the equation as follows

2H2 (g) + O2 (g) →2H2O (g); ∆H =2 (– 242) = – 484 k

Trial Question
Ethane gas is burnt in oxygen to release 3120 kJ of energy. Write a thermochemical
equation for the reaction.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
Solution
2C2H6(g)+7O2(g) 4CO2(g) + 6H2O(l);ΔH= -3120kJ
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
Question
A mole of calcium carbonate decomposes on the absorption
of 177.8 kJ of heat to produce quicklime and a gas. Write a
thermochemical equation for the decomposition.
 FUNDAMENTAL CONCEPTS IN THERMODYNAMICS
Thermochemical Equations
Solution

CaCO3 (s) CaO (s) + CO2 (g) ; ΔH = 177.8 kJ

 ACKNOWLEDGEMENT

The content of presentations herein were adapted

from materials prepared by Dr. Johannes Ami and
Prof. Julius Ahiakpor.

End of Chapter One