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## EP015 Lecture 15L

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# EP015 Lecture 15L

### EP015 Lecture 15L

Chapter 15

16.1 First Law of Thermodynamics.
16.2 Thermodynamics Processes.
16.3 Thermodynamics Work.

CONCEPTUAL MAP : Thermodynamics

15.0 INTRODUCTION

15.0 INTRODUCTION

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

The first to give a concise
definition of the subject was
Scottish physicist William
Thomson in 1854.

LEARNING OUTCOMES : Thermodynamics

15.1 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”.

LEARNING OUTCOMES : Thermodynamics

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

Thermodynamics work, W
done :

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK
The change of internal energy of an ideal gas :
= the change of kinetic energy of the thermal motion
of its molecules.

or

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

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

(point).

In a cyclic process, the
internal energy totally
unchanged.

LEARNING OUTCOMES : Thermodynamics

14.4 MOLAR SPECIFIC HEAT

14.4 MOLAR SPECIFIC HEAT

14.4 MOLAR SPECIFIC HEAT

14.4 MOLAR SPECIFIC HEAT

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

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 :

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

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

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK
Based on the thermodynamic
equation :

Work done in isothermal
process :

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

Conditions for isothermal process :

• The gas must be kept in a good
conductor with thin walls so that
heat can flow in or out of the
system to maintain a constant
temperature.
• The process must be carried out
slowly to allow heat to flow in or out
of the system.

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

Isochoric (or iso-volumetric)
process :
= A thermodynamic process that
occurs at constant volume.

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK
Based on the thermodynamic
equation :

Work done in isochoric process :

Since no work done by the
system, the heat absorbed is
only to increase the
internal energy.

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

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

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK
Based on the thermodynamic
equation :

Work done in isobaric process :

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

When the gas is heated, energy
enters the system and the
temperature increases.

When the gas expands, it does
work to overcome the
atmospheric pressure, which is
constant.

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK
= A thermodynamic process that
occurs at constant heat.

Another related equation :

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

Based on the thermodynamic
equation :

The gas must be kept in a bad
conductor with thick walls so
that heat will not enter or leave
the system.

The process must be carried out fast so that there is
no sufficient time for the heat to flow in or out of the
system.

15.2 & 15.3 THERMODYNAMICS PROCESSES & WORK

Graphical difference between isothermal and