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

אנטרופיה (באנגלית: Entropy) היא מדד תרמודינמי לאי סדר או אקראיות. למערכות עם יותר אי-סדר יש אנטרופיה גבוהה יותר מאשר למערכות עם פחות אי-סדר.
לדוגמה, לשרשרת חומצות אמינו לא מקופלת יש אנטרופיה גבוהה יותר מאשר כאשר השרשרת מקופלת כראוי מכיוון שהשרשרת הליניארית גמישה יותר ולא מאורגנת מאשר חלבון ארוז היטב.
החוק השני של התרמודינמיקה קובע כי האנטרופיה של מערכת מבודדת תמיד גדלה. משמעות הדבר היא שהכל נעשה יותר לא מסודר ללא קלט חיצוני.
מערכות מבודדות מתרחשות לעתים רחוקות באופן טבעי, ולכן התרמודינמיקה בוחנת לעתים קרובות את השינוי באנטרופיה של היקום כולו. השינוי באנטרופיה של היקום כולל הן שינויי אנטרופיה של המערכת הנחקרת והן של סביבתה.
תהליך שבו האנטרופיה של היקום גדלה, כלומר, כזו שיש לה ΔS גדול מאפס, מתרחשת באופן ספונטני. תהליך שבו האנטרופיה פוחתת או שיש לה −ΔS אינו ספונטני וזקוק לקלט אנרגיה כדי להתרחש.

החוק השני של התרמודינמיקה

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בחיפוש אחר מאפיין שעשוי לחזות בצורה מהימנה את הספונטניות של תהליך, נמצא מועמד מבטיח: אנטרופיה. אנטרופיה היא המדד לאקראיות או לחוסר הסדר בתוך מערכת. אנטרופיה גבוהה מצביעה על חוסר סדר גבוה ואנרגיה נמוכה. כדי להבין טוב יותר את האנטרופיה, חשבו על חדר שינה של תלמיד. אם לא נשקיע בו אנרגיה או עבודה, החדר יתבלגן במהירות. זה יתקיים במצב מאוד לא מסודר, מצב של אנטרופיה גבוהה. יש להשקיע אנרגיה במערכת, שהתלמיד יעשה את העבודה וינקה הכל כדי להחזיר את החדר למצב של ניקיון וסדר. מצב זה הוא מצב של אנטרופיה נמוכה.

תהליכים הכוללים עלייה באנטרופיה של המערכת (ΔS > 0) הם לעתים קרובות מאוד ספונטניים; עם זאת, ישנן דוגמאות רבות להיפך. על ידי הרחבת ההתייחסות לשינויים באנטרופיה כך שיכללו גם את הסביבה, אנו עשויים להגיע למסקנה משמעותית לגבי הקשר בין תכונה זו לבין ספונטניות. במודלים תרמודינמיים, המערכת והסביבה כוללים את הכל, כלומר את היקום, ולכן הנוסחה הבאה נכונה:

ΔSuniv = ΔSsys + ΔSsurr

החוק השני של התרמודינמיקה קובע שכל השינויים הספונטניים גורמים לעלייה באנטרופיה של היקום. סיכום של הקשר בין האנטרופיה והספונטניות של התהליך ניתן בטבלה 1.

טבלה 1: הקשר בין האנטרופיה לספונטניות של התהליך.

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<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>ΔSuniv > 0</td>
			<td>ספונטני</td>
		</tr>
		<tr>
			<td>ΔSuniv < 0</td>
			<td>לא ספונטני (ספונטני בכיוון ההפוך)</td>
		</tr>
		<tr>
			<td>ΔSuniv = 0</td>
			<td>בשיווי משקל</td>
		</tr>
	</tbody>
</table>
</div>
</div>

בניסיון לזהות תכונה שעשויה לחזות באופן מהימן את הספונטניות של תהליך, זוהתה מועמדת מבטיחה: אנטרופיה. מדענים...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Energy and Catalysis

אנרגיה וקטליזה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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

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9-12.EVS.1.2

Entropy and Spontaneous Change

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