Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

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Timescales of physical and chemical equilibrium

Background When describing the behaviour of a reacting systems, we usually don't hesitate to apply property models to relate the local properties of each species. For example, in the case of a gas ...
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1answer
44 views

Why are $S = -k_B\sum_i P_i \ln P_i$ and $S = k_B \ln\Omega$ equivalent?

This might be a silly question, but I don't see the equivalence relation between these two equations. Could somebody explain to me how to derive one from the other? Thanks in advance!
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0answers
52 views

Volume Minimization Principle?

I know of two major extremum principles: Entropy Maximization: for a specified $(U,V)$, the equilibrium state has a higher $S$ than all non-equilibrium states, i.e., equilibrium occurs at the maximum ...
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3answers
90 views

The second law of thermodynamics and life on Earth [closed]

The second law of thermodynamics says that order always decreases in a system. The appeareance of life seems to contradict that law, but if we invoke the Sun, everything faals into place again. But ...
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2answers
62 views

Is this SISO (single input single output) or MIMO (multiple instead of single) system?

If I transform wave equation for vibrating string Mx′′+Cx′+Kx=b(t) in linear system using $x_1(t)=x(t)$ and $x_2(t)=x_1^{'}(t)$ vibrating string equation becomes $Md_tx_2(t)+Cx_2(t)+Kx_1(t)=b(t)$. ...
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3answers
77 views

How can we figure out how fast the coffee is warming up the mug? [closed]

The hot coffee is warming up the cold mug. How fast is that happening? Well, to answer that question, we have to know how fast this is happening: The cold mug is cooling down the hot coffee. But ...
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1answer
52 views

How does water at different temperatures behave when they are mixed? [closed]

If I were to inject a constant flow of water at T1 into a reservoir of water at T2, how does that effect the temperature of the mixture at different points in the reservoir? In other words, what ...
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1answer
58 views

Heat loss by gas compression - reversible vs. irreversible

I just solved a problem involving the following scenario: A gas following the van der Waals equation of state (not an ideal gas) is placed in a cylinder and undergoes isothermal compression. The ...
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2answers
30 views

Why can't we use Boltzmann's ideal gas law using temperature in Celsius (intuition)? [closed]

Mathematically, i can see why we won't get the same results when inserting a temperature in Celsius rather than Kelvin(because K=C+273.15), but i can't understand how can a law not "work" for any man ...
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69 views

Dimensional inconsistency in first law of black hole thermodynamics

The first law of black hole mechanics (let's simplify by considering a uncharged and non-rotating black hole) can be written as $$\delta M = T \delta S$$ If I use the definition of Hawking ...
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1answer
50 views

Maximum work obtained by mixing 2 gases

2 boxes containing the same number of moles of 2 ideal identical gases with the same adiabatic index (this is given as gamma), at the same initial temperature Ti but with different volumes, V1 and V2 ...
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0answers
51 views

Why should I discard a carafe if it has ever been heated empty? (Can thermal shock permanently weaken materials without causing them to fail?) [closed]

Related to "What pressure or tension occurs in a glass jar when I pour boiling water inside?" I just got a new coffeemaker, and one of the warnings in the manual states that you should discard the ...
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2answers
69 views

Exact differentials and state functions

I was reading a Wiki article on the relationships between heat capacities And during the derivation I came across this formula (and others like it): This equation was used as a tool in a ...
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0answers
22 views

Rate of Convection

Today in Geophysics the professor briefly introduced the mantle convection processes how it rises and drops. He also said this generates Earths magnetic field and we know that Earth Magnetic field ...
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2answers
39 views

Force over Area diagram [closed]

In this question a have to draw a F/A diagram in function of p-V (pressure-volume) diagram below. I think in a intuitive way that this graphic of F/A it´s going to be the same graphic because ...
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0answers
21 views

Work + heat absorbed in a thermodynamic process

The question describes a simple isobaric closed cycle. The temperature is on the y-axis and volume on the other. There are 4 states. The question asks: ''Find the work done on the gas in the cycle and ...
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0answers
53 views

How is sun's atmosphere (corona) hotter than the surface itself? [duplicate]

Through some research online, I found out that the sun's corona is hotter than it's surface. How's that even possible?? Is the sun releasing it's heat from the surface!!! Need a complete answer.
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1answer
59 views

Will throwing oil on snow help it melt faster (significantly)? [closed]

The main thing that melts snow is the sun. Indeed, without the sun, the air itself would eventually turn to snow. The problem is, the sun melts snow inefficiently. The sun emits radiation (a lot of ...
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27 views

On Rayleigh-Jeans black body distribution derivation

When trying to derive the Rayleigh-Jeans distribution function, all authors say that in k-space each solution of the electromagnetic wave functions(of waves inside a cubic black body) represents an ...
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0answers
31 views

Why are the slopes of the melting and evaporation curves not the same?

I would like to know why the slope of the melting curve, on the left part, isn't the same as the slope of the evaporation curve on the right (or the other way around)? This graph represents the ...
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3answers
97 views

How does pressure cooker work?

If you increase the pressure, the boiling temperature increases as well. In the other direction: if you decrease the pressure enough you could even make water boil at 18 dergees C. However I met this ...
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1answer
37 views

Does a movement of a solid in a liquid generate heat by friction?

We know that if we rubbed two solids, it generates heat. Also the shuttles coming into the atmosphere generates heat. So, likewise does a movement of a solid in a liquid generate heat? Also, what will ...
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2answers
96 views

Can I cook an egg by holding it in thermosphere?

It is known that in thermosphere, air temperature is rising sharply with increase of altitude. In upper atmosphere, temperatures can even reach 2000°C or higher: see 2. However, air there is ...
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1answer
86 views

Thermodynamic free energy

The thermodynamic free energy is defined by $F=U-TS$ with $U,T,S$ being the internal energy, temperature and entropy respectively. I have also seen another formula for the free energy, $F=-T \log{Z}$ ...
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2answers
88 views

Would you save energy by heating the air in a shower stall so that you could use colder water?

It is refreshing to take a cool shower in hot weather. And for the sake of discussion, lets assume that one should be "comfortable" with temeratures when taking a shower. Considering that the vast ...
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23 views

Radiation collapse to black hole

I want to find the temperature at which radiation in AdS will collapse to form a black hole. I have even found a reference that gives the answer but I cannot understand it: ...
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1answer
24 views

How to estimate the maximum temperature between heating a cooling curve?

I have a thermodynamics/mathematical problem I was hoping somebody could help me with. I am simulating the heating and cooling process of several thermal masses connecting through thermal ...
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1answer
39 views

When food cooks, does it gain energy?

I'm just thinking about roasting a chicken in the oven. The heat in the oven does work on the chicken to cook it, but is the same amount of energy dissipated from the oven as is put in, or is some ...
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1answer
40 views

Black Hole Heat Capacity

Why is the specific heat capacity of a black hole given by $C=\frac{\partial M}{\partial T}$? Heat capacity should be ratio of heat change to temperature change so, denoting heat by $Q$, we have ...
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3answers
51 views

Is $\Delta H$ equal to $\Delta Q$?

I will use $\Delta$ to denote "change in something". $\Delta U = \Delta Q+\Delta W$, where the signs have been assumed to be positive (work is done on the system and heat is absorbed). But also ...
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0answers
11 views

why it is said that the mach number of noble gases should be less than 0.1 in order to avoid non linear effects?

while reading about the construction of thermoacoustic refrigeration i read that the mach number of the noble gases should be less than 0.1 to avoid non linear effects. what is the science behind ...
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0answers
38 views

Why do expanding gases lower temperatures around them?

I want to give you an example to my question: When you spray some pressured gas on a surface, liquid water for example, the surface could freeze. but why.. As far as I know molecules close to each ...
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1answer
31 views

Concept question about entropy of surroundings

By Clausius's definition $$dS_{surr} = \frac{\delta q_{rev}}{T}$$ but does this mean $$dS_{surr} = \frac{\delta q}{T}$$ where $\delta q$ is the infinitesimal heat absorbed by the surrounding in any ...
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2answers
123 views

Hotter than the Absolute Hot?

Is the Planck temperature ($1.416×10^{32}$ kelvin), the hottest possible temperature that can ever be reached, with absolute zero as it's opposite analogue ? All I know is a particle with that ...
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why stack width is larger than the thermal and viscous penetration depth in thermoacoustic refrigerator?

The thermal and viscous penetration depth is smaller than the spacing in the stack:this assumption leads to the simplification of Rott‟s functions, where the complex hyperbolic tangents can be set ...
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3answers
67 views

Why during free-expansion, temperature changes for real-gas while the same doesn't happen so for ideal gas?

While reading Free-expansion, I got this: Real gases experience a temperature change during free expansion. For an ideal gas, the temperature doesn't change, [...] I know that temperature ...
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1answer
32 views

Cold Atom Hot Atom 2: Minerals Attracted to Heat

In electric hot water tanks why do calcium quickly form on the heating elements? I watched some one put in a new element. An hour later it stops working. Just to check he took the element and it had ...
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2answers
60 views

When sunlight bounces off the Earth, why isn't the entire spectrum reflected rather than just the infrared portion?

I've read that greenhouse gases absorb and reemit sunlight, and that the infrared portion is what bounces off Earth back to space. When sunlight bounces off the Earth, why isn't the entire spectrum ...
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2answers
53 views

Why do some materials shrink when their temperature increases?

In my vision it would seem quite logical that all materials expand when temperature rises. Because the particles get more energy and travel larger distances when moving. But apparently there are ...
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1answer
40 views

Understanding the relation between pressure, ideal gas and, volume

I was given the following formula which is used for ideal gasses: $$pV = nRT$$ where: p:pressure V: volume n: number of moles R: gasconstant T: temperature now when speaking about vaporpressure ...
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26 views

How much pressure is need to lift tiles against gravity?

Vitrified tiles of size 600 mm by 600 mm and weighing about 7.5 kg each were laid with cement on floor of a building about a year ago. Building has glasses all around and premises are not occupied. I ...
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30 views

Extra 5/2 tau term in chemical potential of a monoatomic ideal gas? [closed]

The chemical potential of an ideal monoatomic gas should be: $\mu = \tau ln \frac {n}{n_Q}$ http://web.mit.edu/ndhillon/www/Teaching/Physics/bookse5.html I get this result if I derive it using the ...
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19 views

Heat Losses to furnaces

I am looking in to the thermal efficiency of a furnace vessel. I am wanting to get a full, or at least better, understanding on the calculations needed to look at the thermal efficiency. So I know ...
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1answer
43 views

Why do i see more steam coming out from the vessel containing water after i turned off the stove? [duplicate]

It is a little observation i did when i was boiling the water. what i observe is that when i turned off the stove on which the water was boiling i could see more steam coming out from it than the ...
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5answers
427 views

Is the Boltzmann constant really that important?

I read a book in which one chapter gave a speech about the fundamental constants of the Universe, and I remember it stated this: If the mass of an electron, the Planck constant, the speed of ...
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0answers
29 views

Volume Operator / volume phase-space-function in thermodynamics

In Thermodynamics, one often encounters the derivation of pressure as the generalised force that belongs to the extensive state-variable of the volume. Postulates: One looks just at a system of many ...
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1answer
31 views

thermodynamic generalized force and thermodynamic potential

I have stumbled across these and have taken some interest. Are the meanings of generalized "force" and "potential" the analogous to the case of mechanics where the derivative of one with respect to a ...
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2answers
49 views

specific heat in solids and liquids

I read a text which said: specific heat of liquids and solids in constant pressure and constant volume does not differ a lot. can some one explain it more?
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4answers
54 views

Electrons flowing through a circuit make it warm, where does that heat come from

in a circuit I have a low resistance device that consumes many watts, in normal operation this device will get warm; where does this heat come from? the law of conservation of energy states that the ...
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2answers
53 views

Thermodynamics identifying an ideal gas

I'm pretty confused. So I've been told that the equation of state for n moles of some type of gas is P(V-b) = nRT. That's not quite like an ideal gas. But then the relations $C_p - C_v = R$, and ...