1 siss termodinamica antonio ballarin denti [email protected]
TRANSCRIPT
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Spettro solare ed intensità energetica Sole Terra
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Flussi di energia solare
The thickness of the arrows represents the amount of energy absorbed, reflected, or stored per unit time in units of watts W.The U.S. consumption per unit time is approximately 3×1012 W
Only a small amount of the total solar energy reaching the earth is fixed by photosynthesis.
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Sistemi aperti,chiusi ed isolati (sistema e ambiente)
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CALORE: non ha le stesse proprietà di un fluido
Heat is transmitted through vacuum;
an indefinite amountof heat can be
extracted from asolid by friction.
These observations
were originally made by Benjamin Thompson
(Count Rumford)
A hot block of the same material and
the same size weigh the same!
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Esperienza di James Prescott Joule: lavoro e calore
a) b)
By transformating various forms of energy into heat inside a calorimeter (an adiabatic container), Joule showed that:
the same amount of heat appeared in the system when
the same amount of any form of energy was dissipated. Thus, if the mechanical and electrical work done in a) and b) is
the same, the temperature changes in both calorimeters will be
equal.
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Il contributo di Joule alla termodinamica fu la scoperta del principio di conservazione dell’energia, ovvero del:
primo principio della termodinamica
∆E = Q-W
Trasformazioni adiabatiche
Trasformazioni isoterme
Trasformazioni isocore
Trasformazioni isobare
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LAVORO
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CAPACITÀ TERMICA
Se V = cost dE = dQ
Nei gas perfetti : E = E(T) e
A
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Se P = cost dQ = dE + PdV
Nei gas perfetti : E = E(T)
B
Per n = 1:
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LA DIREZIONE DEI PROCESSI NATURALIEntropia
Although entropy can be calculated only for a reversible process between two equilibrium paths, all other proceses (including
irreversible) that go between the same initial and final states will have the same change in entropy.
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The total entropy of the system plus the environment does not change during a reversible heat transfer at constant T
Per un processo irreversibile : produzione interna di entropia
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Durante un processo irreversibile:
Entropy and energy behave differently when crossing the boundary of a system. Although the same energy appears inside the system and crosses the boundary, an excess entropy is “generated” inside the system in irreversible processes; we denote this additional amount of entropy by ∆Si
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Indichiamo con 1 un processo reversibile e con 2 un processo irreversibile
ENTROPIA E CALORE
Ma: S1 = S2
Se T1 = T2
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ENTROPIA E LAVORO
CASO 1: processi reversibili
CASO 2: processi irreversibili
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Essendo E funzione di stato :
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Combinando prima e seconda legge:
Vediamo due processi irreversibili
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1) Trasferimento di calore Q da un corpo a temperatura T1 (1) ad un corpo a temperatura T2 (2)
Per i processi spontanei : T1 T2
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2) Espansione isoterma di un gas perfetto nel vuoto
Essendo : T = cost E = E(T) E = 0
Per un processo spontaneo : V2 V1
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ENERGIA LIBERA E POTENZIALI
1. La funzione di stato G ( energia libera di Gibbs )
Introduciamo alcune grandezze fondamentali:
iS = produzione interna di entropia
W’= lavoro utile (al netto del lavoro P – V )
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2. Lavoro utile e G
lavoro utile
lavoro dovuto a trasporto di carica elettrica
lavoro dovuto a trasporto
di massa
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3. Espressione completa di G
Per T e P costanti :
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4. Il potenziale chimico
ni = moli della specie chimica i - esima
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I
I
II
II
∆n
∆n
∆nThe change in free
energy when matter moves across a
boundary can be calculated as the
sum of the individual changes in eachcompartment;
∆Gtotal = ∆G1 + ∆G2
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25All’equilibrio : ∆G = 0 1= 2
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Nei processi spontanei : 1> 2 (∆G = 0)
Se
Detta C la concentrazione si trova sperimentalmente :
1< 2il processo non può avvenire nel senso ( )
Differenziando e integrando :
Tenendo conto del potenziale standard
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5. forma completa del potenziale chimico
Date due regioni con materia a concentrazioni C1 e C2 :
Se T1 = T2 e P1 = P2 e dato che1= 2° °
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Se T1 T2 e P1 P2 :
P = differenza di pressione tra il sistema 1 e 2
T = differenza di temperatura tra 1 e 2
S = entropia molare parziale
V = volume molare parziale
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6. Il potenziale elettrochimico
The work done when a charge q is transported from a region held at potential 1 to a region held at potential
2 can be broken up into two terms.
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Se le masse sono anche cariche
N0 = numero di Avogadro
n = numero di moliz = carica ionee = carica elettrone
F = e N0 = costante di Faraday
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Per una mole ( n = 1 ) :
1. Sia T = 0 , = 0 :
2. Sia P = 0 , = 0 :
3. P = 0 , T = 0 :