{"id":1614,"date":"2026-09-08T08:07:33","date_gmt":"2026-09-08T08:07:33","guid":{"rendered":"https:\/\/maroczain.com\/scolaire.maroczain.com\/?page_id=1614"},"modified":"2026-09-08T08:07:33","modified_gmt":"2026-09-08T08:07:33","slug":"entropie-second-principe-cpge","status":"publish","type":"page","link":"https:\/\/maroczain.com\/scolaire.maroczain.com\/entropie-second-principe-cpge\/","title":{"rendered":"Entropie &amp; Second principe CPGE."},"content":{"rendered":"\n&#8220;`html\n<div id=\"mza-entropie-cpge\">\n\n<style>\n#mza-entropie-cpge,#mza-entropie-cpge *{box-sizing:border-box}\n#mza-entropie-cpge{\n --navy:#06172c;--navy2:#0d416d;--gold:#c99a36;--gold2:#efd68c;\n --paper:#f5f6f8;--white:#fff;--text:#18283a;--muted:#687789;--line:#dfe5eb;\n font-family:Arial,Helvetica,sans-serif;background:var(--paper);color:var(--text);overflow:hidden\n}\n#mza-entropie-cpge a{text-decoration:none;color:inherit}\n#mza-entropie-cpge .wrap{max-width:1200px;margin:auto;padding:0 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var(--line);border-radius:18px;padding:22px;margin-bottom:14px\n}\n#mza-entropie-cpge .exercise h3{color:var(--navy);margin:0 0 10px}\n#mza-entropie-cpge .level{\n display:inline-block;padding:6px 9px;margin-bottom:10px;border-radius:999px;\n background:#f1eee5;color:#7b5b1d;font-size:10px;font-weight:900\n}\n#mza-entropie-cpge .exercise p{color:var(--muted);line-height:1.7}\n#mza-entropie-cpge .hint{\n display:none;margin-top:12px;padding:15px;border-radius:12px;\n background:#eef3f7;color:#425469;line-height:1.65\n}\n#mza-entropie-cpge .qcm{\n background:#fff;border:1px solid var(--line);border-radius:23px;padding:28px\n}\n#mza-entropie-cpge .question{\n padding:20px;margin:15px 0;background:#f7f8fa;border-radius:14px\n}\n#mza-entropie-cpge .question strong{display:block;color:var(--navy);margin-bottom:12px}\n#mza-entropie-cpge label{display:block;padding:8px 0;color:#526174;cursor:pointer}\n#mza-entropie-cpge #entResult{\n display:none;margin-top:18px;padding:20px;border-radius:14px;background:var(--navy);color:#fff\n}\n#mza-entropie-cpge .cta{\n text-align:center;padding:50px 24px;border-radius:25px;\n background:linear-gradient(135deg,#06172c,#0d416d);color:#fff\n}\n#mza-entropie-cpge .cta h2{color:#fff}\n#mza-entropie-cpge .cta p{max-width:760px;margin:0 auto 22px;color:#cfdae4;line-height:1.7}\n\n@media(max-width:900px){\n #mza-entropie-cpge .grid,\n #mza-entropie-cpge .grid3,\n #mza-entropie-cpge .method{grid-template-columns:1fr}\n}\n<\/style>\n\n<header class=\"hero\">\n<div class=\"wrap\">\n\n<span class=\"badge\">COURS 15 \u2022 PHYSIQUE CPGE<\/span>\n\n<h1>\u00c9voluer.<br>Dissiper. Irr\u00e9versibilit\u00e9.<\/h1>\n\n<p class=\"lead\">\nLe second principe donne un sens aux transformations thermodynamiques.\nIl introduit l&#8217;entropie, distingue r\u00e9versibilit\u00e9 et irr\u00e9versibilit\u00e9,\net fixe les limites fondamentales des machines thermiques.\n<\/p>\n\n<div class=\"actions\">\n<a href=\"#cours\" class=\"btn gold\">\ud83d\udcda COMMENCER<\/a>\n<a href=\"#methode\" class=\"btn glass\">\ud83e\udde0 M\u00c9THODE<\/a>\n<a href=\"#exercices\" class=\"btn glass\">\ud83e\udde9 EXERCICES<\/a>\n<a href=\"#qcm\" class=\"btn glass\">\u2753 QCM<\/a>\n<\/div>\n\n<\/div>\n<\/header>\n\n<section id=\"cours\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">1. POURQUOI UN SECOND PRINCIPE ?<\/span>\n<h2>Le premier principe ne suffit pas \u00e0 pr\u00e9voir le sens d&#8217;\u00e9volution.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nLe premier principe exprime la conservation de l&#8217;\u00e9nergie.\nMais il n&#8217;interdit pas, \u00e0 lui seul, qu&#8217;une tasse de caf\u00e9 froide se r\u00e9chauffe spontan\u00e9ment\nau contact d&#8217;une pi\u00e8ce plus froide.\n<\/p>\n\n<p>\nLe second principe introduit une contrainte suppl\u00e9mentaire :\ncertaines transformations compatibles avec l&#8217;\u00e9nergie sont pourtant impossibles spontan\u00e9ment.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">2. ENTROPIE<\/span>\n<h2>Une fonction d&#8217;\u00e9tat thermodynamique.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nL&#8217;entropie S est une fonction d&#8217;\u00e9tat.\nSa variation entre deux \u00e9tats ne d\u00e9pend donc que des \u00e9tats initial et final.\n<\/p>\n\n<div class=\"formula\">\n\u0394S = S\u2082 &#8211; S\u2081\n<\/div>\n\n<p>\nUnit\u00e9 SI :\n<\/p>\n\n<div class=\"formula\">\nJ\u00b7K\u207b\u00b9\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">3. BILAN ENTROPIQUE<\/span>\n<h2>\u00c9change plus cr\u00e9ation.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<div class=\"formula\">\n\u0394S = S<sub>\u00e9chang\u00e9e<\/sub> + S<sub>cr\u00e9\u00e9e<\/sub>\n<\/div>\n\n<p>\navec :\n<\/p>\n\n<div class=\"formula\">\nS<sub>cr\u00e9\u00e9e<\/sub> \u2265 0\n<\/div>\n\n<p>\nPour une transformation r\u00e9versible :\n<\/p>\n\n<div class=\"formula\">\nS<sub>cr\u00e9\u00e9e<\/sub> = 0\n<\/div>\n\n<p>\nPour une transformation irr\u00e9versible :\n<\/p>\n\n<div class=\"formula\">\nS<sub>cr\u00e9\u00e9e<\/sub> &gt; 0\n<\/div>\n\n<\/div>\n<\/section>\n\n<section id=\"methode\" class=\"dark\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\" style=\"color:#efd68c\">MZA ENTROPY ENGINE<\/span>\n<h2>Six r\u00e9flexes pour tout bilan entropique.<\/h2>\n<\/div>\n\n<div class=\"method\">\n<div><b>01<\/b><span>SYST\u00c8ME<\/span><\/div>\n<div><b>02<\/b><span>\u00c9TATS<\/span><\/div>\n<div><b>03<\/b><span>\u00c9CHANGES<\/span><\/div>\n<div><b>04<\/b><span>\u0394S<\/span><\/div>\n<div><b>05<\/b><span>CR\u00c9ATION<\/span><\/div>\n<div><b>06<\/b><span>SENS<\/span><\/div>\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">4. ENTROPIE \u00c9CHANG\u00c9E<\/span>\n<h2>\u00c9change thermique avec une source thermostatique.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour un \u00e9change thermique Q avec un thermostat \u00e0 temp\u00e9rature constante T<sub>e<\/sub> :\n<\/p>\n\n<div class=\"formula\">\nS<sub>\u00e9chang\u00e9e<\/sub> = Q\/T<sub>e<\/sub>\n<\/div>\n\n<p>\nQ est compt\u00e9 positivement s&#8217;il est re\u00e7u par le syst\u00e8me.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">5. CAS R\u00c9VERSIBLE<\/span>\n<h2>Pas de cr\u00e9ation interne d&#8217;entropie.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour une transformation r\u00e9versible :\n<\/p>\n\n<div class=\"formula\">\ndS = \u03b4Q<sub>rev<\/sub>\/T\n<\/div>\n\n<p>\nCette relation permet de calculer une variation d&#8217;entropie en choisissant\nun chemin r\u00e9versible fictif entre deux \u00e9tats.\n<\/p>\n\n<div class=\"tip\">\nComme S est une fonction d&#8217;\u00e9tat, le chemin r\u00e9el peut \u00eatre irr\u00e9versible : on peut n\u00e9anmoins calculer \u0394S \u00e0 l&#8217;aide d&#8217;un chemin r\u00e9versible commode.\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">6. GAZ PARFAIT \u2014 VARIATION D&#8217;ENTROPIE<\/span>\n<h2>Une formule fondamentale.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour n moles d&#8217;un gaz parfait \u00e0 capacit\u00e9s thermiques constantes :\n<\/p>\n\n<div class=\"formula\">\n\u0394S =\nnC<sub>V,m<\/sub> ln(T\u2082\/T\u2081)\n+\nnR ln(V\u2082\/V\u2081)\n<\/div>\n\n<p>\nOn peut \u00e9galement \u00e9crire :\n<\/p>\n\n<div class=\"formula\">\n\u0394S =\nnC<sub>P,m<\/sub> ln(T\u2082\/T\u2081)\n&#8211;\nnR ln(P\u2082\/P\u2081)\n<\/div>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">7. ISOTHERME D&#8217;UN GAZ PARFAIT<\/span>\n<h2>Une expression tr\u00e8s simple.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nSi T est constante :\n<\/p>\n\n<div class=\"formula\">\n\u0394S = nR ln(V\u2082\/V\u2081)\n<\/div>\n\n<p>\nou :\n<\/p>\n\n<div class=\"formula\">\n\u0394S = -nR ln(P\u2082\/P\u2081)\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">8. ISOCHORE D&#8217;UN GAZ PARFAIT<\/span>\n<h2>Le volume ne change pas.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<div class=\"formula\">\n\u0394S = nC<sub>V,m<\/sub> ln(T\u2082\/T\u2081)\n<\/div>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">9. ISObare D&#8217;UN GAZ PARFAIT<\/span>\n<h2>La pression reste constante.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<div class=\"formula\">\n\u0394S = nC<sub>P,m<\/sub> ln(T\u2082\/T\u2081)\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">10. ADIABATIQUE R\u00c9VERSIBLE<\/span>\n<h2>Transformation isentropique.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour une transformation adiabatique r\u00e9versible :\n<\/p>\n\n<div class=\"formula\">\n\u03b4Q = 0\n<\/div>\n\net :\n\n<div class=\"formula\">\nS<sub>cr\u00e9\u00e9e<\/sub>=0\n<\/div>\n\ndonc :\n\n<div class=\"formula\">\n\u0394S = 0\n<\/div>\n\n<p>\nUne adiabatique r\u00e9versible est donc isentropique.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">11. ADIABATIQUE IRR\u00c9VERSIBLE<\/span>\n<h2>Attention au pi\u00e8ge classique.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nAdiabatique signifie seulement :\n<\/p>\n\n<div class=\"formula\">\nQ = 0\n<\/div>\n\n<p>\nMais si la transformation est irr\u00e9versible :\n<\/p>\n\n<div class=\"formula\">\n\u0394S = S<sub>cr\u00e9\u00e9e<\/sub> &gt; 0\n<\/div>\n\n<div class=\"tip\">\nR\u00e9flexe concours : adiabatique ne veut pas dire isentropique, sauf si la transformation est \u00e9galement r\u00e9versible.\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">12. D\u00c9TENTE LIBRE<\/span>\n<h2>Un exemple majeur d&#8217;irr\u00e9versibilit\u00e9.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nUn gaz parfait se d\u00e9tend dans le vide d&#8217;un volume V\u2081 vers un volume V\u2082&gt;V\u2081.\n<\/p>\n\n<p>\nPour un syst\u00e8me isol\u00e9 id\u00e9alement :\n<\/p>\n\n<div class=\"formula\">\nQ=0\n<\/div>\n\n<div class=\"formula\">\nW=0\n<\/div>\n\ndonc :\n\n<div class=\"formula\">\n\u0394U=0\n<\/div>\n\n<p>\nPour un gaz parfait, T reste alors constante.\n<\/p>\n\n<p>\nMais :\n<\/p>\n\n<div class=\"formula\">\n\u0394S = nR ln(V\u2082\/V\u2081) &gt; 0\n<\/div>\n\n<p>\nToute l&#8217;augmentation d&#8217;entropie est cr\u00e9\u00e9e int\u00e9rieurement.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">13. CONTACT THERMIQUE ENTRE DEUX CORPS<\/span>\n<h2>La chaleur s&#8217;\u00e9coule spontan\u00e9ment du chaud vers le froid.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nDeux corps \u00e0 temp\u00e9ratures diff\u00e9rentes sont mis en contact dans une enceinte isol\u00e9e.\n<\/p>\n\n<p>\nL&#8217;\u00e9nergie totale se conserve, mais l&#8217;entropie totale augmente :\n<\/p>\n\n<div class=\"formula\">\n\u0394S<sub>total<\/sub> &gt; 0\n<\/div>\n\n<p>\njusqu&#8217;\u00e0 l&#8217;\u00e9quilibre thermique.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">14. SYST\u00c8ME ISOL\u00c9<\/span>\n<h2>Forme essentielle du second principe.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour un syst\u00e8me isol\u00e9 :\n<\/p>\n\n<div class=\"formula\">\nS<sub>\u00e9chang\u00e9e<\/sub> = 0\n<\/div>\n\ndonc :\n\n<div class=\"formula\">\n\u0394S = S<sub>cr\u00e9\u00e9e<\/sub> \u2265 0\n<\/div>\n\n<p>\nL&#8217;entropie d&#8217;un syst\u00e8me isol\u00e9 ne peut pas diminuer spontan\u00e9ment.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">15. MACHINE THERMIQUE<\/span>\n<h2>Transformer une partie de la chaleur en travail.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nUne machine thermique cyclique \u00e9change typiquement :\n<\/p>\n\n<ul>\n<li>une chaleur Q<sub>chaud<\/sub> avec une source chaude ;<\/li>\n<li>une chaleur Q<sub>froid<\/sub> avec une source froide ;<\/li>\n<li>un travail W avec l&#8217;ext\u00e9rieur.<\/li>\n<\/ul>\n\n<p>\nSur un cycle :\n<\/p>\n\n<div class=\"formula\">\n\u0394U = 0\n<\/div>\n\ndonc :\n\n<div class=\"formula\">\nW + Q<sub>chaud<\/sub> + Q<sub>froid<\/sub> = 0\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">16. RENDEMENT D&#8217;UN MOTEUR<\/span>\n<h2>Quelle part de la chaleur re\u00e7ue devient du travail utile ?<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour un moteur thermique :\n<\/p>\n\n<div class=\"formula\">\n\u03b7 = W<sub>utile<\/sub>\/Q<sub>chaud,re\u00e7u<\/sub>\n<\/div>\n\n<p>\navec :\n<\/p>\n\n<div class=\"formula\">\n0 &lt; \u03b7 &lt; 1\n<\/div>\n\n<p>\nAucune machine cyclique ne peut transformer int\u00e9gralement en travail\nla chaleur re\u00e7ue d&#8217;une seule source thermique.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">17. MACHINE DE CARNOT<\/span>\n<h2>La limite th\u00e9orique de performance.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour une machine r\u00e9versible fonctionnant entre une source chaude T<sub>h<\/sub>\net une source froide T<sub>c<\/sub> :\n<\/p>\n\n<div class=\"formula\">\n\u03b7<sub>Carnot<\/sub> = 1 &#8211; T<sub>c<\/sub>\/T<sub>h<\/sub>\n<\/div>\n\n<p>\nLes temp\u00e9ratures doivent \u00eatre exprim\u00e9es en kelvins.\n<\/p>\n\n<div class=\"tip\">\nLe rendement de Carnot d\u00e9pend uniquement des temp\u00e9ratures des deux sources.\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">18. IN\u00c9GALIT\u00c9 DE CLAUSIUS<\/span>\n<h2>Une autre \u00e9criture du second principe.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<p>\nPour un cycle :\n<\/p>\n\n<div class=\"formula\">\n\u222e \u03b4Q\/T \u2264 0\n<\/div>\n\n<p>\nL&#8217;\u00e9galit\u00e9 correspond \u00e0 un cycle r\u00e9versible.\n<\/p>\n\n<\/div>\n<\/section>\n\n<section style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">19. R\u00c9VERSIBILIT\u00c9<\/span>\n<h2>Un id\u00e9al utile mais exigeant.<\/h2>\n<\/div>\n\n<div class=\"grid3\">\n\n<div class=\"card\">\n<h3>\u00c9carts infinit\u00e9simaux<\/h3>\n<p>\nLes \u00e9changes doivent se faire sous des diff\u00e9rences infinit\u00e9simales de temp\u00e9rature, pression ou potentiel.\n<\/p>\n<\/div>\n\n<div class=\"card\">\n<h3>Pas de dissipation<\/h3>\n<p>\nPas de frottement, viscosit\u00e9 dissipative, effet Joule non compens\u00e9 ou turbulence irr\u00e9versible.\n<\/p>\n<\/div>\n\n<div class=\"card\">\n<h3>\u00c9volution quasi-statique<\/h3>\n<p>\nLe syst\u00e8me reste arbitrairement proche de l&#8217;\u00e9quilibre.\n<\/p>\n<\/div>\n\n<\/div>\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">20. SOURCES D&#8217;IRR\u00c9VERSIBILIT\u00c9<\/span>\n<h2>Reconna\u00eetre ce qui cr\u00e9e de l&#8217;entropie.<\/h2>\n<\/div>\n\n<div class=\"grid\">\n\n<div class=\"card\">\n<h3>Frottements<\/h3>\n<p>Dissipation m\u00e9canique.<\/p>\n<\/div>\n\n<div class=\"card\">\n<h3>Conduction thermique<\/h3>\n<p>\u00c9change sous diff\u00e9rence finie de temp\u00e9rature.<\/p>\n<\/div>\n\n<div class=\"card\">\n<h3>D\u00e9tente libre<\/h3>\n<p>Expansion sans pression ext\u00e9rieure oppos\u00e9e.<\/p>\n<\/div>\n\n<div class=\"card\">\n<h3>Effet Joule<\/h3>\n<p>Dissipation \u00e9lectrique dans une r\u00e9sistance.<\/p>\n<\/div>\n\n<\/div>\n<\/div>\n<\/section>\n\n<section id=\"exercices\" style=\"background:#efede7\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">21. EXERCICES PROGRESSIFS<\/span>\n<h2>Calculer \u0394S puis identifier la cr\u00e9ation.<\/h2>\n<\/div>\n\n<div class=\"exercise\">\n<span class=\"level\">NIVEAU 1<\/span>\n<h3>Exercice 1 \u2014 Chauffage isochore<\/h3>\n<p>\nUne mole de gaz parfait est chauff\u00e9e \u00e0 volume constant de T\u2081 \u00e0 T\u2082.\nExprimer sa variation d&#8217;entropie.\n<\/p>\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntHint('eHint1')\">\ud83d\udca1 INDICE<\/button>\n<div id=\"eHint1\" class=\"hint\">\n\u00c0 volume constant, le terme en ln(V\u2082\/V\u2081) dispara\u00eet.\n<\/div>\n<\/div>\n\n<div class=\"exercise\">\n<span class=\"level\">NIVEAU 2<\/span>\n<h3>Exercice 2 \u2014 D\u00e9tente isotherme<\/h3>\n<p>\nUn gaz parfait subit une d\u00e9tente isotherme de V\u2081 \u00e0 V\u2082.\nD\u00e9terminer \u0394S.\n<\/p>\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntHint('eHint2')\">\ud83d\udca1 INDICE<\/button>\n<div id=\"eHint2\" class=\"hint\">\nUtilisez \u0394S=nR ln(V\u2082\/V\u2081).\n<\/div>\n<\/div>\n\n<div class=\"exercise\">\n<span class=\"level\">NIVEAU 3<\/span>\n<h3>Exercice 3 \u2014 D\u00e9tente libre<\/h3>\n<p>\nUn gaz parfait double son volume par d\u00e9tente libre dans une enceinte isol\u00e9e.\nDiscuter Q, W, \u0394U, \u0394T et \u0394S.\n<\/p>\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntHint('eHint3')\">\ud83d\udca1 INDICE<\/button>\n<div id=\"eHint3\" class=\"hint\">\nLa transformation est adiabatique, mais fortement irr\u00e9versible.\n<\/div>\n<\/div>\n\n<div class=\"exercise\">\n<span class=\"level\">NIVEAU PR\u00c9PA<\/span>\n<h3>Exercice 4 \u2014 Moteur de Carnot<\/h3>\n<p>\nUne machine fonctionne entre T\u2095 et T\ud835\ude8c.\nExprimer le rendement maximal th\u00e9orique.\n<\/p>\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntHint('eHint4')\">\ud83d\udca1 INDICE<\/button>\n<div id=\"eHint4\" class=\"hint\">\nLe rendement maximal d&#8217;une machine r\u00e9versible d\u00e9pend uniquement des deux temp\u00e9ratures absolues.\n<\/div>\n<\/div>\n\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">22. PROBLEM LAB<\/span>\n<h2>Mission : moteur thermique r\u00e9el contre moteur id\u00e9al.<\/h2>\n<\/div>\n\n<div class=\"card\">\n\n<h3>Situation<\/h3>\n\n<p>\nUn moteur thermique re\u00e7oit une chaleur Qh d&#8217;une source chaude \u00e0 temp\u00e9rature Th,\nrejette une chaleur Qc vers une source froide \u00e0 Tc et fournit un travail utile.\nSon rendement r\u00e9el est inf\u00e9rieur au rendement de Carnot.\n<\/p>\n\n<p>Votre mission :<\/p>\n\n<ol>\n<li>\u00e9crire le bilan \u00e9nerg\u00e9tique sur un cycle ;<\/li>\n<li>d\u00e9finir clairement le rendement du moteur ;<\/li>\n<li>calculer le rendement de Carnot ;<\/li>\n<li>comparer rendement r\u00e9el et rendement maximal ;<\/li>\n<li>\u00e9tablir le bilan d&#8217;entropie du moteur et des sources ;<\/li>\n<li>identifier o\u00f9 appara\u00eet la cr\u00e9ation d&#8217;entropie ;<\/li>\n<li>expliquer pourquoi les frottements diminuent le rendement ;<\/li>\n<li>expliquer l&#8217;effet d&#8217;une augmentation de Th ;<\/li>\n<li>expliquer l&#8217;effet d&#8217;une diminution de Tc ;<\/li>\n<li>proposer trois am\u00e9liorations physiques permettant de rapprocher le syst\u00e8me d&#8217;un fonctionnement plus r\u00e9versible.<\/li>\n<\/ol>\n\n<div class=\"actions\">\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntHint('eMission1')\">\ud83d\udca1 INDICE<\/button>\n<button type=\"button\" class=\"btn\" style=\"background:#06172c;color:#fff\" onclick=\"mzaEntHint('eMission2')\">\ud83e\udde0 M\u00c9THODE<\/button>\n<\/div>\n\n<div id=\"eMission1\" class=\"hint\">\nCommencez par s\u00e9parer strictement bilan d&#8217;\u00e9nergie et bilan d&#8217;entropie. Ils r\u00e9pondent \u00e0 deux questions diff\u00e9rentes.\n<\/div>\n\n<div id=\"eMission2\" class=\"hint\">\nProc\u00e9dez dans l&#8217;ordre : cycle \u2192 premier principe \u2192 rendement \u2192 Carnot \u2192 \u00e9changes entropiques \u2192 cr\u00e9ation d&#8217;entropie \u2192 origine des irr\u00e9versibilit\u00e9s.\n<\/div>\n\n<\/div>\n<\/div>\n<\/section>\n\n<section class=\"dark\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\" style=\"color:#efd68c\">MZA ENTROPY CHECK<\/span>\n<h2>Les six r\u00e9flexes du second principe.<\/h2>\n<\/div>\n\n<div class=\"method\">\n<div><b>A<\/b><span>\u0394S<\/span><\/div>\n<div><b>B<\/b><span>\u00c9CHANGE<\/span><\/div>\n<div><b>C<\/b><span>CR\u00c9ATION<\/span><\/div>\n<div><b>D<\/b><span>R\u00c9VERSIBILIT\u00c9<\/span><\/div>\n<div><b>E<\/b><span>CARNOT<\/span><\/div>\n<div><b>F<\/b><span>SENS<\/span><\/div>\n<\/div>\n\n<\/div>\n<\/section>\n\n<section id=\"qcm\">\n<div class=\"wrap\">\n\n<div class=\"head\">\n<span class=\"kicker\">23. QCM DE VALIDATION<\/span>\n<h2>Diagnostic Entropie &#038; Second principe CPGE.<\/h2>\n<p>Le score est affich\u00e9 sans r\u00e9v\u00e9ler les r\u00e9ponses correctes.<\/p>\n<\/div>\n\n<div class=\"qcm\">\n\n<form id=\"entQuiz\">\n\n<div class=\"question\">\n<strong>1. Pour une transformation irr\u00e9versible :<\/strong>\n<label><input type=\"radio\" name=\"e1\" value=\"1\"> S cr\u00e9\u00e9e est strictement positive<\/label>\n<label><input type=\"radio\" name=\"e1\" value=\"0\"> S cr\u00e9\u00e9e est toujours nulle<\/label>\n<label><input type=\"radio\" name=\"e1\" value=\"0\"> \u0394S est toujours n\u00e9gative<\/label>\n<label><input type=\"radio\" name=\"e1\" value=\"0\"> Q est toujours nul<\/label>\n<\/div>\n\n<div class=\"question\">\n<strong>2. Pour une transformation r\u00e9versible :<\/strong>\n<label><input type=\"radio\" name=\"e2\" value=\"1\"> S cr\u00e9\u00e9e = 0<\/label>\n<label><input type=\"radio\" name=\"e2\" value=\"0\"> \u0394S = 0 dans tous les cas<\/label>\n<label><input type=\"radio\" name=\"e2\" value=\"0\"> Q = 0 dans tous les cas<\/label>\n<label><input type=\"radio\" name=\"e2\" value=\"0\"> W = 0 dans tous les cas<\/label>\n<\/div>\n\n<div class=\"question\">\n<strong>3. Une transformation adiabatique irr\u00e9versible peut v\u00e9rifier :<\/strong>\n<label><input type=\"radio\" name=\"e3\" value=\"1\"> Q=0 et \u0394S&gt;0<\/label>\n<label><input type=\"radio\" name=\"e3\" value=\"0\"> Q=0 et \u0394S=0 n\u00e9cessairement<\/label>\n<label><input type=\"radio\" name=\"e3\" value=\"0\"> Q&gt;0 obligatoirement<\/label>\n<label><input type=\"radio\" name=\"e3\" value=\"0\"> S cr\u00e9\u00e9e&lt;0<\/label>\n<\/div>\n\n<div class=\"question\">\n<strong>4. Pour un syst\u00e8me isol\u00e9 :<\/strong>\n<label><input type=\"radio\" name=\"e4\" value=\"1\"> \u0394S\u22650<\/label>\n<label><input type=\"radio\" name=\"e4\" value=\"0\"> \u0394S\u22640 toujours<\/label>\n<label><input type=\"radio\" name=\"e4\" value=\"0\"> \u0394S=0 toujours<\/label>\n<label><input type=\"radio\" name=\"e4\" value=\"0\"> Q&gt;0 toujours<\/label>\n<\/div>\n\n<div class=\"question\">\n<strong>5. Le rendement maximal entre Th et Tc vaut :<\/strong>\n<label><input type=\"radio\" name=\"e5\" value=\"1\"> 1-Tc\/Th<\/label>\n<label><input type=\"radio\" name=\"e5\" value=\"0\"> 1-Th\/Tc<\/label>\n<label><input type=\"radio\" name=\"e5\" value=\"0\"> Tc\/Th<\/label>\n<label><input type=\"radio\" name=\"e5\" value=\"0\"> Th+Tc<\/label>\n<\/div>\n\n<div class=\"question\">\n<strong>6. Une d\u00e9tente libre d&#8217;un gaz parfait isol\u00e9 est :<\/strong>\n<label><input type=\"radio\" name=\"e6\" value=\"1\"> irr\u00e9versible avec cr\u00e9ation d&#8217;entropie<\/label>\n<label><input type=\"radio\" name=\"e6\" value=\"0\"> r\u00e9versible et isentropique<\/label>\n<label><input type=\"radio\" name=\"e6\" value=\"0\"> n\u00e9cessairement isotherme r\u00e9versible<\/label>\n<label><input type=\"radio\" name=\"e6\" value=\"0\"> impossible<\/label>\n<\/div>\n\n<button type=\"button\" class=\"btn gold\" onclick=\"mzaEntScore()\">\nVALIDER MON QCM\n<\/button>\n\n<\/form>\n\n<div id=\"entResult\"><\/div>\n\n<\/div>\n<\/div>\n<\/section>\n\n<section>\n<div class=\"wrap\">\n\n<div class=\"cta\">\n\n<div style=\"font-size:43px\">\u0394S = S\u00e9chang\u00e9e + Scr\u00e9\u00e9e<\/div>\n\n<h2>L&#8217;\u00e9nergie se conserve, mais sa capacit\u00e9 \u00e0 produire du travail se d\u00e9grade.<\/h2>\n\n<p>\nLe second principe donne le sens des transformations, mesure l&#8217;irr\u00e9versibilit\u00e9\net fixe les limites physiques des moteurs, r\u00e9frig\u00e9rateurs et machines thermiques.\n<\/p>\n\n<div class=\"actions\" style=\"justify-content:center\">\n<a href=\"#cours\" class=\"btn gold\">\ud83d\udcda REVOIR LE COURS<\/a>\n<a href=\"#exercices\" class=\"btn glass\">\ud83e\udde9 EXERCICES<\/a>\n<a href=\"#qcm\" class=\"btn glass\">\u2753 REFAIRE LE QCM<\/a>\n<\/div>\n\n<\/div>\n<\/div>\n<\/section>\n\n<script>\nfunction mzaEntHint(id){\n const el=document.getElementById(id);\n if(!el)return;\n el.style.display = el.style.display===\"block\" ? \"none\" : \"block\";\n}\n\nfunction mzaEntScore(){\n const form=document.getElementById(\"entQuiz\");\n const result=document.getElementById(\"entResult\");\n\n let score=0;\n let complete=true;\n\n [\"e1\",\"e2\",\"e3\",\"e4\",\"e5\",\"e6\"].forEach(function(name){\n   const answer=form.querySelector('input[name=\"'+name+'\"]:checked');\n   if(!answer){\n     complete=false;\n   }else{\n     score+=Number(answer.value);\n   }\n });\n\n result.style.display=\"block\";\n\n if(!complete){\n   result.innerHTML=\"<strong>R\u00e9pondez aux 6 questions avant de valider.<\/strong>\";\n   return;\n }\n\n const pct=Math.round(score\/6*100);\n\n let level=\"Second principe \u00e0 consolider\";\n if(pct>=50) level=\"Fondations acquises\";\n if(pct>=67) level=\"Bon niveau\";\n if(pct>=84) level=\"Tr\u00e8s bonne ma\u00eetrise\";\n if(pct===100) level=\"Excellent niveau CPGE\";\n\n result.innerHTML=\n \"<strong style='font-size:30px;color:#efd68c'>\"+pct+\"%<\/strong>\"+\n \"<p><b>\"+level+\"<\/b><\/p>\"+\n \"<p>Score : \"+score+\" \/ 6<\/p>\"+\n \"<p>Les r\u00e9ponses correctes et la correction d\u00e9taill\u00e9e restent masqu\u00e9es.<\/p>\";\n}\n<\/script>\n\n<\/div>\n&#8220;`\n","protected":false},"excerpt":{"rendered":"<p>&#8220;`html COURS 15 \u2022 PHYSIQUE CPGE \u00c9voluer.Dissiper. Irr\u00e9versibilit\u00e9. Le second principe donne un sens aux transformations thermodynamiques. Il introduit l&#8217;entropie, distingue r\u00e9versibilit\u00e9 et irr\u00e9versibilit\u00e9, et fixe les limites fondamentales des machines thermiques. \ud83d\udcda COMMENCER \ud83e\udde0 M\u00c9THODE \ud83e\udde9 EXERCICES \u2753 QCM 1. POURQUOI UN SECOND PRINCIPE ? Le premier principe ne suffit pas \u00e0 pr\u00e9voir le [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1614","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/pages\/1614","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/comments?post=1614"}],"version-history":[{"count":1,"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/pages\/1614\/revisions"}],"predecessor-version":[{"id":1616,"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/pages\/1614\/revisions\/1616"}],"wp:attachment":[{"href":"https:\/\/maroczain.com\/scolaire.maroczain.com\/wp-json\/wp\/v2\/media?parent=1614"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}