3.3 Second Law of Thermodynamics and Entropy

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What is Entropy S ?

J/K
a measure of disorder or randomness in a system and thus the uncertainty or unpredictability pf data.
quantifies the number of ways microscopic components can be arranged.
Higher entropy means more disorder.

<ul><li><p><span style="color: oklch(0.872 0.01 258.338)">J/K</span></p></li><li><p><span style="color: oklch(0.872 0.01 258.338)">a measure of disorder or randomness in a system and thus the uncertainty or unpredictability pf data.</span></p></li><li><p><span style="color: oklch(0.872 0.01 258.338)">quantifies the number of ways microscopic components can be arranged. </span></p></li><li><p><span style="color: oklch(0.872 0.01 258.338)">Higher entropy means more disorder.</span></p></li></ul><p></p>

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What becomes the entropy equation if the process is isothermal ?

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What is the second law of thermodynamics ?

if a process is applied : Consider a certain amount of gas enclosed in a cylinder–piston chamber and an external compressive force is applied on the piston to decrease the chamber’s volume

In a closed system, the entropy of the system increases for irreversible processes

It remains constant for reversible processes and never decreases

<p><strong>if a process is applied : Consi</strong><span>der </span><strong>a</strong><span> </span><strong>certa</strong><span>in </span><strong>amou</strong><span>nt </span><strong>o</strong><span>f </span><strong>g</strong><span>as </span><strong>enclo</strong><span>sed </span><strong>i</strong><span>n </span><strong>a</strong><span> </span><strong>cylin</strong><span>der–</span><strong>pist</strong><span>on </span><strong>chamb</strong><span>er </span><strong>a</strong><span>nd </span><strong>a</strong><span>n </span><strong>exter</strong><span>nal </span><strong>compres</strong><span>sive </span><strong>for</strong>ce is <strong>appli</strong>ed <strong>o</strong>n <strong>t</strong>he <strong>pist</strong>on <strong>t</strong>o <strong>decre</strong>ase <strong>t</strong>he <strong>chamb</strong>er’<strong>s</strong> <strong>volu</strong>me</p><p><strong>I</strong>n <strong>a</strong> <strong>clos</strong>ed <strong>syst</strong>em, <strong>t</strong>he <strong>entro</strong>py <strong>o</strong>f <strong>t</strong>he <strong>syst</strong>em <strong>increa</strong>ses <strong>f</strong>or <strong>irrevers</strong>ible <strong>proces</strong>ses </p><p><strong>It remai</strong>ns <strong>const</strong>ant <strong>f</strong>or <strong>reversi</strong>ble <strong>proces</strong>ses and <strong>nev</strong>er <strong>decrea</strong>ses</p>

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What is the cycle of carnot ?

A Carnot engine is a perfect imaginary heat engine.
It:

takes in heat from something hot,
uses that heat to move or push (it “does work”),
then throws away some leftover heat to something cold.

<p>A <strong>Carnot engine</strong> is a perfect imaginary heat engine.<br>It:</p><ul><li><p><strong>takes in heat</strong> from something hot,</p></li><li><p><strong>uses that heat to move or push</strong> (it “does work”),</p></li><li><p>then <strong>throws away some leftover heat</strong> to something cold.</p></li></ul><p></p>

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Describe the 4 stages of a carnot cycle (and draw the T-S diagram)

ab – Isothermal Expansion
Heat Q_H enters from the hot reservoir at constant temperature T_H
The gas expands and does work.
bc – Adiabatic Expansion
No heat exchange.
The gas keeps expanding, so it cools down (from T_H to T_L).
cd – Isothermal Compression
Heat Q_L is released to the cold reservoir at constant temperature T_L.
The gas is compressed.
da – Adiabatic Compression
No heat exchange
The gas is compressed, so it heats up (from T_L back to T_H).

Area within loop cycle = net useful work generated by the system

<ul><li><p><strong>ab – Isothermal Expansion</strong><br>Heat Q_H enters from the hot reservoir at constant temperature T_H<br>The gas expands and does work.</p></li><li><p><strong>bc – Adiabatic Expansion</strong></p><p>No heat exchange.<br>The gas keeps expanding, so it cools down (from T_H to T_L).</p></li><li><p><strong>cd – Isothermal Compression</strong><br>Heat Q_L is released to the cold reservoir at constant temperature T_L.<br>The gas is compressed.</p></li><li><p><strong>da – Adiabatic Compression</strong><br>No heat exchange<br>The gas is compressed, so it heats up (from T_L back to T_H).</p></li></ul><p>Area within loop cycle = net useful work generated by the system</p>

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What is the relationship between heat and useful work in a carnot cycle ?

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what is the relationship between Q-H, T_H & Q_L & T_L ? write the demonstration

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What is the fomula for the efficiency of a carnot cycle using Work and Heat exchanged ? Write the demonstration

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What is the formula for the efficiency of a carnot cycle using temperatures ?

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Is the efficiency formula an idealization ? What Would be missing ?

Yes, it depends of the fluid used or the internal structure and design of the engine

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