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CHAPTER 2
THE FIRST LAW OF THERMOYNAMICS
Group 5
1. Riduan
2. Novita Sari3. Putri Eka Nurhikmah Sari
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SOME BASIC UNDERSTANDING
Some basic understanding of thermoynamics is
much related to:
system and environment,
the state of the system and the equation of
state,
State function, Changes in circumstances,
Heat and work.
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4
system and environment :transfer of energy (E) & materr (m)
System(Focus of attentoin)
environment
environment
environment
An open system Closed System Isolated System
environment
E
&
m E
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5
Open
mass & energyShift:
Closed
Energy
Isolated
Di not happen anything
SYSTEM
ENVIRONMENT
6.2
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The State of The System
the state variabel system :
n (the amount of substance)
V (volume)
p (pressure)
T (temperature)
E.g. Gas equation of state:pV = nRT
p = p (n, T, V)
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Condition function
Condition function is each system
characteristic which only concerned with
beginning condition and final condition
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In thermodinamic we know some
condition function :
In energy (u; U)
Entalphy (h; H),
Entropi (s; S),
Gibbs free energy (g; G),
Helmholtz free energy (a; A).
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One of the important characteristic of
differential condition function is total
differential (differential ekstrak),some of total
differrential characteristic are:
2
1. if dz = z2z1, so dz is a
1
Total diferenial
2. If dz = 0, so dz is a total diferential
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3. occurred Euler formula:
if dz = M(x,y) dx + N(x,y) dy so
M N
= (2.1)
y x x y
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Changing condition :
The process which occurred in a system can be
consist of:
1. Reversibel process is a process which
system always in equilibrium condition or
quasy-static
2. Irreversibel process is process which cannt
fulfil reversibel process
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2.1.6 Work
Work is a form of energy that is not ketiap heatexchanged between the system and theenvironment
Figure 2.2. Work exchange between the systemwith its environment
W (+) W(-)
Environment
System
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Sorts of forms of work:
1. electrical work2. mechanical work
3. magnetic work
4. work volume
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work volume
1. Expansion work one step
Expansion work is the work that occurs whenthe system volume swell against pressure
environment.
Work performed by the system: W = mgh
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Expansion work one step
M
M
T.P1.V1
T.P2.V2
S
S
S
S
S
S
S
Sh
(a) Start state (b) Final state
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W=-P1V
W=-P1(V2-V1) (2.5)
W = the total work that accompanies the system
state changes
P1 = pressure outside (environment) caused mass
V2 = volume of the system at the final state
V2 = volume of the system at the initial state
(-) = Adjust system that works
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P1.V1
P2
P1
P2.V2
}rentangP1V1 V2 V
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P1P2
Equation 2.5 is not just for work expansion,
but also the work of compression
In compression, V2
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2. Two-step expansion work
If the state of the system is determined on
the state of his three so-called two-stepexpansion work (2-stroke)
W = W + W first step second step (2.6)
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Expansion work two step
VV2
P1
P1
P1
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The shaded area stating the amount of
work that occurs in a two-step expansion.objec changes to the system with more
steps will be accompanied by greater job.
The shaded area in the two-step systemthat works greater than the work one step.
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P
P
P
P1.V1
P2.V2
V1 V V2 V
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Pl is the pressure of the environment outside
the detention system can be consideredequal to the system pressure (P), Pl = P, so
that equation (2.6) becomes
dW = -P dV (2.7)
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The total number of workers who produced
the reversible expansion can be obtained byintegrating equation (2.7)