Name: entropy and spontaneous change
Uploaded: 2023-04-30T10:08:43.000Z
Duration: 1 min 14 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Environmental Science

ecosystems-interactions-energy-and-dynamics

Ecosystems: Interactions Energy and Dynamics

9-12.EVS.1.1

The Second Law of Thermodynamics

L'entropia, abbreviata in S, è la misura termodinamica del disordine o della casualità. I sistemi con più disordine hanno un'entropia più alta rispetto a quelli con meno disordine.
Ad esempio, una catena di amminoacidi dispiegata ha un'entropia più elevata rispetto a quando la catena è ripiegata correttamente perché la catena lineare è più flessibile e disorganizzata di una proteina strettamente impacchettata.
La seconda legge della termodinamica afferma che l'entropia di un sistema isolato aumenta sempre. Ciò significa che tutto diventa più disordinato senza input esterni.
I sistemi isolati raramente si verificano in natura, quindi la termodinamica spesso esamina il cambiamento di entropia dell'intero universo. Il cambiamento nell'entropia dell'universo include sia i cambiamenti di entropia del sistema studiato che dei suoi dintorni.
Un processo in cui l'entropia dell'universo aumenta, cioè uno che ha un ΔS maggiore di zero, avviene spontaneamente. Un processo in cui l'entropia diminuisce o ha un -ΔS non è spontaneo e ha bisogno di un input di energia per verificarsi.

la seconda legge della termodinamica

Nella ricerca di una proprietà che possa prevedere in modo affidabile la spontaneità di un processo, è stata identificata una candidata promettente: l'entropia. Gli scienziati si riferiscono alla misura della casualità o del disordine all'interno di un sistema come entropia. Un'alta entropia significa un alto disordine e bassa energia. Per comprendere meglio l'entropia, pensa alla camera da letto di uno studente. Se non venisse applicata energia o lavoro, la stanza diventerebbe rapidamente disordinata. Esisterebbe in uno stato molto disordinato, uno di alta entropia. È necessario inserire energia nel sistema, sotto forma di lavoro dello studente e sistemare ogni cosa, per riportare la stanza a uno stato di pulizia e ordine. Questo stato è uno di bassa entropia.

I processi che comportano un aumento dell'entropia del sistema (ΔS > 0) sono molto spesso spontanei; tuttavia, esistono molti esempi in contrario. Espandendo la considerazione dei cambiamenti dell'entropia per includere l'ambiente circostante, possiamo giungere a una conclusione significativa riguardo alla relazione tra questa proprietà e la spontaneità. Nei modelli termodinamici, il sistema e l'ambiente circostante comprendono tutto, ovvero l'universo, e quindi vale quanto segue:

ΔS_univ = ΔS_sys + ΔS_surr

La seconda legge della termodinamica afferma che tutti i cambiamenti spontanei causano un aumento dell'entropia dell'universo. Una sintesi della relazione tra entropia e spontaneità del processo è riportata nella tabella 1.

Tabella 1: Relazione tra entropia e spontaneità del processo.

<table style="border-collapse: collapse; border: 1px solid black;">
	<tbody>
		<tr>
			<td style="border: 1px solid black; padding: 5px;">ΔS_univ ></td>
			<td style="border: 1px solid black; padding: 5px;">spontaneo</td>
		</tr>
		<tr>
			<td style="border: 1px solid black; padding: 5px;">ΔS_univ <</td>
			<td style="border: 1px solid black; padding: 5px;">non spontaneo (spontaneo nella direzione opposta)</td>
		</tr>
		<tr>
			<td style="border: 1px solid black; padding: 5px;">ΔS_univ =</td>
			<td style="border: 1px solid black; padding: 5px;">at equilibrium</td>
		</tr>
	</tbody>
</table>

Questo testo è adattato da Openstax, Biologia 2e, <a href="https://openstax.org/books/biology-2e/pages/6-3-the-laws-of-thermodynamics">Section 6.3: The Laws of Thermodynamics</a> e Openstax, Chimica 2e, <a href="https://openstax.org/books/chemistry-2e/pages/16-3-the-second-and-third-laws-of-thermodynamics">16.3 The Second and Third Laws of Thermodynamics.</a>

La Seconda Legge della Termodinamica

Nella ricerca di una proprietà che possa prevedere in modo affidabile la spontaneità di un processo, è stato identificato un candidato promettente: l'entropia. Scienziati...

Education

Didattica

JoVE Core

Cell Biology

Biologia cellulare

Unit 1

Unità 1

Energy and Catalysis

Energia e Catalisi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

entropy and spontaneous change

Entropy helps predict whether a process will happen on its own. Entropy is a measure of randomness or disorder in a system. High entropy means high disorder and low energy. A student’s bedroom is a simple example. If no work is done, the room becomes messy over time. That messy state is highly disordered and has high entropy. To make the room clean again, energy must be added as the student puts things away. That organized state has low entropy.

Processes that increase the entropy of the system, written as ΔS &gt; 0, are often spontaneous. Spontaneous means a process can occur without outside help. However, there are many exceptions. To understand spontaneity more fully, entropy changes in the surroundings must also be included. In thermodynamic models, the system and its surroundings make up the universe. The total change in entropy is written as ΔSuniv = ΔSsys + ΔSsurr.

The second law of thermodynamics connects entropy with spontaneous change. It states that all spontaneous changes increase the entropy of the universe. If ΔSuniv is greater than 0, the process is spontaneous. If ΔSuniv is less than 0, the process is nonspontaneous, although the opposite direction would be spontaneous. If ΔSuniv equals 0, the system is at equilibrium.

Entropy and Spontaneous Change

the first law of thermodynamics

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the second law of thermodynamics

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Entropy and Spontaneous Change | JoVE K12

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9-12.EVS.1.2

Entropy and Spontaneous Change

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