Laatste berichten
-
19:47
Bruine vlekken op treinaanwijzerbord 10
-
19:44
Vogels in de stad zijn goede klussers 2
-
19:12
Rood laserlicht 3
-
19:07
wig 1
-
17:30
Herleiden afmetingen vanaf een foto 21
-
16:34
[wiskunde] Prijs Product per KG; Alternatief Inzicht 3
-
13:57
do-re-mi-fa-so vliegtuigen 9
-
13:16
geen minkowski-ruimte toch? Doe ik dit nou fout? 17
-
13:12
[natuurkunde] kroon van koning op Syracuse 10
-
12:01
Gravity and gravitation 1
-
10:15
2013 – Augustus Vraag 3 3
-
24 apr
Vraag 2009 Juli Vraag 5 5
-
24 apr
positie 2
-
24 apr
Schroefdraad berekening 8
-
24 apr
[scheikunde] Kan chloorgas de geleiding van elektriciteit belemmeren? 9
-
23 apr
Weerfrustratie 9
-
23 apr
Kunnen quantum Zonnecellen 190% quantum efficiënt zijn 3
-
23 apr
De Euro Nederlandse 100 qubit computer komt eraan
-
23 apr
projectiel 8
-
23 apr
Verschil tussen deze 2 vragen 5
Nieuwsberichten
-
04 mar
Een nieuw soort magnetisme: altermagnetisme
-
31 okt
AI kan via stem diabetes vaststellen 11
-
21 okt
Einstein krijgt wéér gelijk 45
-
07 feb
witter dan wit 20
-
19 jun
irrigatie en de aardas
Entropie
Moderator: physicalattraction
Forumregels
(Middelbare) school-achtige vragen naar het forum "Huiswerk en Practica" a.u.b.
Zie eerst de Huiswerkbijsluiter
(Middelbare) school-achtige vragen naar het forum "Huiswerk en Practica" a.u.b.
Zie eerst de Huiswerkbijsluiter
-
- Berichten: 3.437
Re: Entropie
Entropie is een maat voor de hoeveelheid "wanorde" in je systeem. Een perfect kristal heeft heel weinig wanorde, en daarom een lage entropie. Warme is zeer wanordelijk (in de zin dat je het niet in symmetrieen enzo kan vangen) en daarom heeft warmte een heel hoge entropie. Er is een wet die zegt dat de entropie altijd moet toenemen, en daarom snap je dan ook dat een kristal wel uit elkaar kan vallen in losse delen, maar dat deze losse delen niet vanzelf weer een kristal zullen vormen.
Never underestimate the predictability of stupidity...
-
- Berichten: 88
Re: Entropie
Het is wel belangrijk om op te merken dat locaal de entropie wel kan afnemen, maar dat dat er voor zorgt dat elders de entropie nog groter wordt. IJs dat kristalliseert verkleint locaal de wanorde, maar de warmt edie er bij vrijkomt zal elders de wanorde doen toenemen.
-
- Berichten: 5.679
Re: Entropie
Om deze reden is het ontstaan van complex leven ook logisch: de atomen waar een mens uit is opgebouwd hebben misschien een lager entropieniveau dan eerst, maar de mens heeft de wanorde in de wereld om hem heen beslist doen toenemenHet is wel belangrijk om op te merken dat locaal de entropie wel kan afnemen, maar dat dat er voor zorgt dat elders de entropie nog groter wordt. IJs dat kristalliseert verkleint locaal de wanorde, maar de warmt edie er bij vrijkomt zal elders de wanorde doen toenemen.
In theory, there's no difference between theory and practice. In practice, there is.
-
- Berichten: 1.279
Re: Entropie
Maar hoe bereken je die wanorde? Wanorde is toch subjectief? Volgens mij is mijn kamer zeer ordelijk maar volgens mama...
-
- Berichten: 5.679
Re: Entropie
Valt wel uit te drukken in objectieve maten. Gelijkmatigheid van verdeling (variantie e.d.) van energie- en massadichtheid bijvoorbeeld.Maar hoe bereken je die wanorde? Wanorde is toch subjectief? Volgens mij is mijn kamer zeer ordelijk maar volgens mama...
In theory, there's no difference between theory and practice. In practice, there is.
-
- Berichten: 7.224
Re: Entropie
Maar hoe bereken je die wanorde? Wanorde is toch subjectief? Volgens mij is mijn kamer zeer ordelijk maar volgens mama...
Die wanorde kan berekend worden met behulp van statistische verdelingen. Hiervoor is het vakgebied statististische fysica / statistische mechanica. Echter geen koek en ei.
If I have seen further it is by standing on the shoulders of giants.-- Isaac Newton
-
- Berichten: 3.437
Re: Entropie
Natuurkundigen definieren de mate van wanorde door middel van het aantal verschillende manieren waarop een bepaalde toestand "gemaakt" kan worden. Overigens is dat een definitie die eigenlijk alleen maar goed op microscopisch niveau te gebruiken is (omdat op microscopisch niveau je allerlei identieke deeltjes hebt).
Never underestimate the predictability of stupidity...
-
- Berichten: 62
Re: Entropie
Ik mis 'n aantal dingen in de uitleg van mijn voorgangers 8) . Ik heb hier ooit 's wat over geschreven in het Engels, wat ik hier nu maar even verbatim kopiëer (heb nu even geen tijd om te vertalen, sorry).
Entropy is not heat. The two are fundamentally different.
There are two forms of energy: work and heat. Work can be subdivided into various kinds, heat cannot. Work is associated with the directional movement of particles (i.e. when a gas expands against a piston, the system then doing work on its surroundings). Heat is associated with the non-directional (random) motion of particles.
The First Law of Thermodynamics states that energy is conserved, i.e. the total amount of energy in the universe is constant and is equal to the sum of heat and work. In symbols (and in the simplest form possible):
U = Q + W
U: internal energy of the system (in this case the universe), expressed in Joules.
Q: the amount of energy in the form of heat, expressed in Joules.
W: the amount of energy in the form of work, expressed in Joules.
For the universe or an isolated system within it, the First Law requires that Q = -W. This shows that energy can be converted from one form into the other, without ever being consumed. Note that the First Law says nothing about the direction in which processes may (or may not) occur.
The Second Law of Thermodynamics states that the amount of entropy in the universe or in an isolated system within it, cannot decrease. There are various descriptions of entropy, all of which are equivalent (though this fact is far from obvious and requires a lot of thought and training).
First, you have the classical description, which arose when people started to examine the workings of steam engines. This description of entropy defines it as the ratio of transferred heat divided by temperature:
S = Q / T
S: entropy, expressed in J/K (Joules per Kelvin).
Q: the amount of energy in the form of heat, expressed in Joules.
T: the temperature, expressed in Kelvins, 0 Kelvin being absolute zero.
To see how this classical definition of entropy introduces irreversibility (i.e. prescribes a direction), consider a system with temperature Tsys that radiates an amount Q of heat to its surroundings. The entropy change of the system associated with this transfer is Q / Tsys (by convention, the sign of this quantity is negative as the system "loses" heat to its surroundings). The entropy change of the surroundings is Q / Tsurr (likewise, by convention, the sign of this quantity is positive as it gains heat from the system). Now if Tsurr > Tsys, then the total entropy change of the universe due to this transfer of heat is negative, which the Second Law forbids. In other words, this formulation of entropy states that heat cannot flow from a cold object to a hot one. It does not refer in any way to notions like order, particles or randomness. It does not involve ANY notion about what it is that matter is made of (i.e. molecules, atoms, etc). It describes but does not offer a mechanism.
Second, you have the statistical description, which defines entropy as a function of the number of states accessible to a system. I won't get into what a state is in this context, because I'd have to bring in quantum mechanics and all that. This description of entropy is based explicitly on the molecular nature of matter and does offer a mechanism. As an analogy, think of a pawn on a chessboard. If the pawn can only be on square A1 and all other squares are inaccessible to it, then the entropy of the system is defined to be 0. If the pawn can be anywhere on the first row, then the entropy rises above 0. If it can be anywhere on the board, the entropy rises some more. Mathematically, the entropy is defined as follows:
S = k ln D
S: entropy, expressed in J/K (Joules per Kelvin).
k: Boltzmann's constant, equal to appr. 1.4 x 10-23 Joules per Kelvin (J/K).
D: the number of accessible states (dimensionless).
ln: the natural logarithm.
This formulation of entropy states that in the universe or an isolated system within it, only those processes are allowed to occur that increase D (and thus S).
Third, you have information entropy, which I will not get into (if you must know, then Google it).
The Third Law of Thermodynamics states that absolute zero cannot be attained in a finite number of steps. At absolute zero, D = 1 so S = 0.
So much for the basic laws of themodynamics and the various descriptions of entropy. I choose not to present the very important notion of free energy, which combines energetic and entropic effects to predict whether or not a process can occur spontaneously. There are various sites on the web that explain it formally.
Entropy is not heat. The two are fundamentally different.
There are two forms of energy: work and heat. Work can be subdivided into various kinds, heat cannot. Work is associated with the directional movement of particles (i.e. when a gas expands against a piston, the system then doing work on its surroundings). Heat is associated with the non-directional (random) motion of particles.
The First Law of Thermodynamics states that energy is conserved, i.e. the total amount of energy in the universe is constant and is equal to the sum of heat and work. In symbols (and in the simplest form possible):
U = Q + W
U: internal energy of the system (in this case the universe), expressed in Joules.
Q: the amount of energy in the form of heat, expressed in Joules.
W: the amount of energy in the form of work, expressed in Joules.
For the universe or an isolated system within it, the First Law requires that Q = -W. This shows that energy can be converted from one form into the other, without ever being consumed. Note that the First Law says nothing about the direction in which processes may (or may not) occur.
The Second Law of Thermodynamics states that the amount of entropy in the universe or in an isolated system within it, cannot decrease. There are various descriptions of entropy, all of which are equivalent (though this fact is far from obvious and requires a lot of thought and training).
First, you have the classical description, which arose when people started to examine the workings of steam engines. This description of entropy defines it as the ratio of transferred heat divided by temperature:
S = Q / T
S: entropy, expressed in J/K (Joules per Kelvin).
Q: the amount of energy in the form of heat, expressed in Joules.
T: the temperature, expressed in Kelvins, 0 Kelvin being absolute zero.
To see how this classical definition of entropy introduces irreversibility (i.e. prescribes a direction), consider a system with temperature Tsys that radiates an amount Q of heat to its surroundings. The entropy change of the system associated with this transfer is Q / Tsys (by convention, the sign of this quantity is negative as the system "loses" heat to its surroundings). The entropy change of the surroundings is Q / Tsurr (likewise, by convention, the sign of this quantity is positive as it gains heat from the system). Now if Tsurr > Tsys, then the total entropy change of the universe due to this transfer of heat is negative, which the Second Law forbids. In other words, this formulation of entropy states that heat cannot flow from a cold object to a hot one. It does not refer in any way to notions like order, particles or randomness. It does not involve ANY notion about what it is that matter is made of (i.e. molecules, atoms, etc). It describes but does not offer a mechanism.
Second, you have the statistical description, which defines entropy as a function of the number of states accessible to a system. I won't get into what a state is in this context, because I'd have to bring in quantum mechanics and all that. This description of entropy is based explicitly on the molecular nature of matter and does offer a mechanism. As an analogy, think of a pawn on a chessboard. If the pawn can only be on square A1 and all other squares are inaccessible to it, then the entropy of the system is defined to be 0. If the pawn can be anywhere on the first row, then the entropy rises above 0. If it can be anywhere on the board, the entropy rises some more. Mathematically, the entropy is defined as follows:
S = k ln D
S: entropy, expressed in J/K (Joules per Kelvin).
k: Boltzmann's constant, equal to appr. 1.4 x 10-23 Joules per Kelvin (J/K).
D: the number of accessible states (dimensionless).
ln: the natural logarithm.
This formulation of entropy states that in the universe or an isolated system within it, only those processes are allowed to occur that increase D (and thus S).
Third, you have information entropy, which I will not get into (if you must know, then Google it).
The Third Law of Thermodynamics states that absolute zero cannot be attained in a finite number of steps. At absolute zero, D = 1 so S = 0.
So much for the basic laws of themodynamics and the various descriptions of entropy. I choose not to present the very important notion of free energy, which combines energetic and entropic effects to predict whether or not a process can occur spontaneously. There are various sites on the web that explain it formally.
Growing older is mandatory. Growing up is not.
-
- Berichten: 718
Re: Entropie
Boltzmann heeft de entropie op deze manier gedefinieerd lang voordat er quantummechanica bestond. Bovendien gaat het niet om het aantal bereikbare toestanden maar om het aantal micro-toestanden (bijvoorbeeld alle mogelijke posities en impulsen van alle moleculen van een gas) dat compatibel is met een bepaalde macro-toestand (druk, temperatuur volume).Second, you have the statistical description, which defines entropy as a function of the number of states accessible to a system. I won't get into what a state is in this context, because I'd have to bring in quantum mechanics and all that.
Vergeet niet erbij te zeggen dat deze vorm van entropie uit de informatietheorie/ coderingstheorie komt en niet uit de thermodynamica (geintroduceerd door Claude Shannon van Bell telephone company.Third, you have information entropy, which I will not get into (if you must know, then Google it).
Googelen op Shannon and Weaver levert veel informatie op).
Re: Entropie
S = k ln D
The Third Law of Thermodynamics states that absolute zero cannot be attained in a finite number of steps. At absolute zero, D = 1 so S = 0.
Als het absolute nulpunt (van temperatuur) niet kan bereikt worden in de realiteit van ons universum (bijna oneindig, maar eindig aantal stappen), komt er ook nooit een moment dat alles energieloze massa zou zijn (vermits temperatuur bepaald is door kinetische energie)
-
- Berichten: 575
Re: Entropie
Misschien een laat antwoord maar meer info over entropie en thermodynamica in het algemeen kan je vinden op :
http://users.telenet.be/bawi/stoom/Thermodynamica.htm
en
http://users.telenet.be/bawi/stoom/Entropie.htm
Groetjes, Wim
http://users.telenet.be/bawi/stoom/Thermodynamica.htm
en
http://users.telenet.be/bawi/stoom/Entropie.htm
Groetjes, Wim
