EP015 Note 9

KOLEJ MATRIKULASI KEJURUTERAAN JOHOR

KEMENTERIAN PENDIDIKAN MALAYSIA

CHAPTER 9 : KINETIC THEORY OF GASES AND THERMODYNAMICS

9.1 Kinetic Theory of Gases.
9.2 Molecular Kinetic Energy & Internal Energy.
9.3 Molar Specific Heats.
9.4 First Law of Thermodynamics.
9.5 Thermodynamics Processes.
9.6 Thermodynamics Work.

SLT (HOURS)

Lecture : 2.5

Tutorial :7

Practical :0

Ind. Learning : 9.5

TOTAL : 19

9.0 INTRODUCTION

Gas is one of three classical states of matter.
A pure gas may be made up of individual
atoms, molecules, or compounds.

What distinguishes a gas from liquids and
solids is the vast separation of the individual
gas particles. This separation usually makes
a colorless gas invisible to the human
observer.

9.1 KINETIC THEORY OF GASES
LEARNING OUTCOMES

9.1 KINETIC THEORY OF GASES

One of the basic methods used to describe gases is the
kinetic theory of ideal gas based on the following
assumptions :

▪ The attractive force between the molecules is
negligible.

▪ The volume of the molecules is negligible compared
with the volume of the gas in the container.

▪ Molecules are like perfectly elastic spheres. Collisions
between molecules and with the walls are perfectly
elastic.

▪ The time during a collision is very small when
compared to the time between two successive
collisions.

9.1 Kinetic Theory of Gases

Combination of Boyle’s, Charles’s and Pressure laws
produce the ideal gas equation, i.e. :

where nR = constant.
n = number of mole.
R = molar gas constant = 8.31 J mol-1 K-1

or

9.1 Kinetic Theory of Gases

Ideal gas are always undergoing random non-stop
translation (linear) motion which is related closely to
temperature.
The average of molecular translational kinetic energy
(average of kinetic energy of every gas molecule) is
represented as follow :

The root mean square of the speed :

9.1 Kinetic Theory of Gases

The speed is closely related to temperature.
Based on the general :

Therefore, the relationship between root mean square
speed and temperature is as follow:

or

M = mass of 1 mole gas (with unit of kg mol-1)

9.1 Kinetic Theory of Gases

9.2 MOLECULAR KINETIC ENERGY & INTERNAL ENERGY
LEARNING OUTCOMES

9.2 MOLECULAR KINETIC ENERGY & INTERNAL ENERGY
The total molecular translational kinetic energy
(average of kinetic energy of gas) is represented as :

or

9.2 Molecular Kinetic Energy & Internal Energy

Degree of freedom, f :
= the number of
independent ways by
which a molecule can
process energy.

It refers to the number of
independent variables
required to determine the
specific location and
spatial orientation of a
body.

9.2 Molecular Kinetic Energy & Internal Energy

The principle of Equipartition of Energy states that :
“When a certain amount of energy is supplied to a system, each of the
possible degrees of freedom will receive an equal share of the total energy

supplied.”
The kinetic energy for each translational and rotational degree of freedom of

a molecule is ½ kT.

9.2 Molecular Kinetic Energy & Internal Energy

The internal energy of an ideal gas :
= the kinetic energy of the thermal motion of its molecules.

The total energy (internal energy) in a gas :

or

9.2 Molecular Kinetic Energy & Internal Energy

9.4 FIRST LAW OF THERMODYNAMICS
LEARNING OUTCOMES

9.4 FIRST LAW OF THERMODYNAMICS
Thermodynamics is the study of energy
conversion between heat and mechanical work,
and subsequently the macroscopic variables
such as temperature, volume and pressure.

9.4 First Law of Thermodynamics

The first law of thermodynamics states that :
“The total energy in a closed system is constant (the heat, Q is
distributed into the change of internal energy, U and the energy to do

external work, W”.

9.4 First Law of Thermodynamics

9.5 THERMODYNAMICS PROCESSES
LEARNING OUTCOMES

9.6 THERMODYNAMICS WORK
LEARNING OUTCOMES

9.5 THERMODYNAMICS PROCESSES
Thermodynamics work, W done :

9.5 Thermodynamics Processes

The change of internal energy of an ideal gas :
= the change of kinetic energy of the thermal motion of

its molecules.

or

9.5 Thermodynamics Processes

Cyclic process :
= A process that starts and ends at the same state

(point).
In a cyclic process, the internal
energy totally unchanged.

9.5 Thermodynamics Processes

Thermodynamic process :
= A transformation from the state of equilibrium described by the

parameter (p1,V1,T1) to another state (p2,V2,T2).

Generally, there are 4 types of the thermodynamics process :

9.5 Thermodynamics Processes

Isothermal process :
= A thermodynamic process that occurs
at constant temperature.

Work done in isothermal process :

Based on the thermodynamic
equation :

9.5 Thermodynamics Processes

Isochoric (or iso-volumetric) Work done in isochoric process :
process :
= A thermodynamic process that Since no work done by the system, the
occurs at constant volume. heat absorbed is only to increase the
internal energy.
Based on the thermodynamic
equation :

9.5 Thermodynamics Processes

Isobaric process :
= A thermodynamic process that
occurs at constant pressure.

Based on the thermodynamic Work done in isobaric process :
equation :

9.5 Thermodynamics Processes

Adiabatic process :
= A thermodynamic process that
occurs at constant heat.

Another related equation :

Based on the thermodynamic
equation :

9.5 Thermodynamics Processes

Graphical difference between isothermal and
adiabatic processes :

9.5 Thermodynamics Processes

9.3 MOLAR SPECIFIC HEATS
LEARNING OUTCOMES

9.3 MOLAR SPECIFIC HEATS

9.3 Molar Specific Heats

9.3 Molar Specific Heats

KOLEJ MATRIKULASI KEJURUTERAAN JOHOR

KEMENTERIAN PENDIDIKAN MALAYSIA

KOLEJ MATRIKULASI KEJURUTERAAN JOHOR

KEMENTERIAN PENDIDIKAN MALAYSIA