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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363 views

Temperature of thermochemical reaction between propane and nitrous oxide

I'm trying to calculate the properties of the combustion process using propane and nitrous oxide. When I tried to nail down the combustion temperature, the result looks just off to me. I went through ...
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1answer
98 views

Thermodynamics and Energy conservation in the Scope of the Universe

According to the 2nd law of thermodynamics, no system can be a 100% efficient. Looking at the universe as it's own system, is it an exception to the rule (a system that doesn't lose any energy)? If ...
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1answer
96 views

How to derive following thermodynamic relation?

I'd would like to derive the following $$\bigg(\frac{\partial U}{\partial V}\bigg)_T = T \bigg(\frac{\partial p}{\partial T}\bigg)_V - p$$ What I know is that the internal energy $U$ is a function ...
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1answer
432 views

Why uniform ensemble and microcanonical ensemble are the same in thermodynamic limit?

So uniform ensemble is the ensemble of all possible states with energy less than E, and since entropy derived from both are equivalent with each other in the thermodynamic limit, many functions ...
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1answer
296 views

Calculating phase diagrams (Calphad)

I am calculating the phase diagrams for Li-Mg binary alloy with reference to the following text: http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5600701 In the equation used in the above ...
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1answer
107 views

Textbook Problem: Free energy expression

In Klotz, Introduction to Chemical Thermodynamics, Ex. 8.2 requires me to derive $$ dG = V \left( \frac{\partial p}{\partial V} \right)_V dV + \left[ V \left( \frac{\partial p}{\partial T} ...
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3answers
617 views

Shouldn't the sign of generated entropy always be positive?

I have a process where 10 g of liquid lead at 400 C is dropped into a water bath that is at 25 C. The lead solidifies over time and comes to thermal equilibrium with the water bath. The bath is so ...
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1answer
359 views

What is the physical basis behind thermal diffusion in a Clusius-Dickel column?

A Clusius-Dickel column allows separation of two species by the application of a thermal gradient. In its simplest form, two bulbs are maintained at two different temperatures $T_1$ and $T_2$ and ...
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1answer
3k views

Can water exist as liquid in a vacuum chamber at room temperature?

I know boiling point at vacuum is far below the room temperature. But I still wondering if the humidity reaches the saturated humidity (100% relative humidity), will the vapor condense to liquid, ...
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1answer
125 views

What are the state functions telling me or how are they related to total energy?

I am quite new to thermodynamics and statistical mechanics so this might be an easy question: In thermodynamics you get a bunch of thermodynamics potentials, so as for example enthalpy, internal ...
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2answers
166 views

A box with cooler and heater on opposite faces

Suppose there's a box with one face cold, and the opposite face hot. So when the air molecules hit the cooler face, it will transfer its momentum and energy to the wall, bouncing back with less ...
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1answer
147 views

Solid in Liquid Heat Transfer

If there is a solid immersed in a large (but finite) pool of water, where the solid has temperature $T_s$ and the water has temperature $T_w$, with $T_w>T_s$, how can I calculate $T_s(t)$ and ...
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1answer
104 views

Finding cooling time using an impulse of heat energy

A chip has a thermal resistance of 0.007 K/J s and thermal capacitance of 1.6 J/K. You give it an impulse of heat equal to 100 J. How long does it take for the chip to cool to within 10% of the ...
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2answers
592 views

How would a change in ambient temp affect a radiator?

I'm curious if you have a radiator or say a block of metal (lets say it's copper since it has the highest thermal conductivity) and on one side is a processor producing heat. At idle the processor ...
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2answers
366 views

Does the black body emit more than any other type of body?

I found this on Wikipedia article on black bodies: A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The ...
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1answer
3k views

How long does it take a warm object to cool in air?

This is a work-related question. A warm steel torus of a given diameter & thickness is left in a room held at a controlled temperature, how long does it take to reach equilibrium? Assume the air ...
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3answers
6k views

Why is Entropy expressed in terms of Enthalpy?

Why does ${\Delta}S_{m(fusion)} = \frac{{\Delta}H_{m(fusion)}}{T}$ ? I always thought ${\Delta}S = \frac{dQ}{T}$ In this case does it mean $dQ = {\Delta}H$ ?? Why is it so?
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2answers
932 views

Difficulties with understanding total entropy change and unavailabillty

Of course, I know the fact that the entropy of an isolated system never decreases. Neverthless what makes me confused about the entropy(or change of entropy) of an isolated system is the explanation ...
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1answer
1k views

Sensible heat question (solving for temperature)

If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water. Using $Q = mc(t_2-t_1)$ or ...
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1answer
54 views

Reconciling Units in Jeans' Criterion Formula

In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as: $\frac{GmM}{R_c} = \frac{3mkT}{2}$ ... To me this suggests that on the left we have Joules, and on the right we have ...
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3answers
1k views

Why the temperature is getting lower when the universe is expanding

As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the ...
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1answer
385 views

The definition of entropy

As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
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1answer
409 views

Clausius Clapeyron equation

While reading about the Clausius Clapeyron equation from the Feynman lectures on Physics, I couldn't understand a few things from its derivation: Although the argument was pretty clear, when the ...
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1answer
367 views

free energy and entropy of 2D soap froth

This is a (exploratory) computational project. The soap froth was created by injecting bubbles into a chamber formed by two rectangular plates which are 0.16cm. From the moment the soap froth was ...
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3answers
948 views

Why is an air conditioner more efficient in a low-thermal-mass house?

Why is an air conditioner more efficient in a low-thermal-mass house? I recently read To get these efficiency gains it is important to use the air conditioner as it is intended: the unit has to ...
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1answer
152 views

Where does the energy flow differ between a forward and reverse process?

Mathematically ($W=\int PdV$) and by the First Law, I understand that $1 \rightarrow 4 \rightarrow 3 \rightarrow 2 \rightarrow 1$ and $1 \rightarrow 2 \rightarrow 3 \rightarrow 4 \rightarrow 1$ are ...
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1answer
305 views

Are Carnot theorem and Carnot Cycle related?

This has been in my head for a while, and I think I finally have the answer. I was wondering what was so special about the Carnot cycle so it was used to demonstrate the Carnot theorem; the ...
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1answer
199 views

What are the properties and impediments of a liquid air fueled engine?

I recently came across a very interesting article that suggested the possibility of using liquified gases like air, nitrogen, or oxygen as a power source for cars. It appears that this company is ...
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1answer
143 views

Could we really charge metal plates using microwaves?

While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
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1answer
314 views

Zero entropy change

If you put a object in contact with a heat reservoir that is infinitesimally higher in temperature than the object and allow equilibrium to be reached the entropy change is zero right?
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1answer
110 views

Is Joule heating only between charged particles?

The Wikipedia page for Joule heating explains "It is now known that Joule heating is caused by interactions between the moving particles that form the current (usually, but not always, electrons) and ...
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5answers
11k views

Why does burning magnesium explode when sprinkled with water?

Magnesium powder burns extremely well and reaches temperatures of 2500°C. However, attempts to extinguish such a magnesium fire with conventional water (e.g. from a garden hose) only make it worse: ...
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1answer
149 views

Where is the critical moment where the microcanonical ensemble enters the justification for the equilibium state?

As explained in many books, for the microscopic justification of the second law of thermodynamics (lets formulate it as the total entropy takes maximum among all possible exchanges of two systems), ...
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1answer
330 views

Amount/flow rate of N2 needed to cool substrate

I'm trying to cool a substrate inside a vacuum chamber with liquid nitrogen. The substrate holder is a block of copper suspended from the top of the chamber via nylon screws (for thermal insulation). ...
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1answer
207 views

Thermodynamics and cross entropy

I am facing with the concept of cross entropy. I would like to know the thermodynamic and statistical meaning of cross entropy (if exists)?
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2answers
273 views

How would I go about solving this transient convection problem if the mean fluid temperature is constantly changing?

Let's say I have a ceramic slab on a conveyor belt that is initially at $450\,^{\circ}\mathrm{C}$ and there is air being blown over it at a speed of $35 \frac{m}{s}$ with an ambient temperature of ...
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1answer
209 views

nature of glass transition

I am reading in some book: "The glass transition is similar in appearance to a second-order phase transition, but it is not a true thermodynamic phase transition. This is because the transition ...
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1answer
854 views

How should a heat current be defined for two component system with unequal numbers

I'm trying to calculate a heat current in a linear response regime of a very weakly-interacting two component low temperature Fermi gas with imbalanced population. I think there are two standard ways ...
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1answer
413 views

Joining the definitions of entropy

$\int \frac{Q_{rev}}{T} = \Delta(k_B\ln\Omega)=\Delta S$ Could anyone give some definite proof for this? I was able to prove that the two definitions of change in entropy are equivalent for an ...
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1answer
2k views

Heat Flux and Spatial Temperature Gradients

The derivation for Heat Equation I am reading starts by stating Net change of heat inside $[x,x+\Delta x]$ = Net flux of heat across boundaries + Total heat generated inside $[x,x+\Delta x]$ and ...
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1answer
237 views

Do all closed systems, only considering kinematic/mechanical principles, exhibit time reversal symmetry?

It makes a lot of sense to me to imagine a cannonball flying through space as not so much experiencing a macroscopic non-conservative drag force, but as pushing a bunch of air molecules and giving ...
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3answers
120 views

Certain material heating water in a recipient

I don't know how to resolve a problem, but I don't want the answer since I'm almost going to have it resolved. What the problem says is we have 85 liters of water at 7ºC in an iron pot of 29kg. We ...
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1answer
490 views

Thermodynamic System: Windmill

There is a closed system that is just a windmill attached to a rotating shaft that can mechanically power something. I know the system produces work on the surroundings from the rotating shaft and ...
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1answer
209 views

Does thermodynamic processess affect phase transition in solid state metals

I read an article about phase transitions and I read about thermodynamic processes such as Adiabatic process, Isochoric process, Isobaric process, Isothermal process Do these processes affect phase ...
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1answer
1k views

What is wrong with this reasoning on chemical potential?

One definition of the chemical potential is the change of internal energy of the system with respect to a particle of the added substance with the system entropy, molar volume, and all other species ...
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1answer
295 views

Vapor pressure higher than equilibrium vapor pressure

Is there any mechanism by which the vapor pressure of a liquid substance (lets say in a vacuum) is measured to be greater than the expected saturated vapor pressure at that temperature? Specifically, ...
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1answer
830 views

Temperature vs AC energy consumption

I'm need to understand the following: to keep the room at confortable temperature (70 degree, for example), how does the amount of energy consumed by the AC grow as the outside air temperature rises ...
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1answer
242 views

Solar heating of an object in air

I need a solution to the heat equation that shows temp increase in an object, e.g. a cube or sphere, in sunlight. The object is assumed to be exposed on all sides except one. It is a solid object ...
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4answers
211 views

What is planetary surface temperature given constant sub-surface temperature?

If a planet of radius $R_1$ has a constant sub-surface temperature $T_0$ at $R_0<R_1$, what is the long-term equilibrium surface temperature $T_1$? Say we assume constant thermal diffusivity of ...
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0answers
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Constancy of Coefficients of Additive Integrals Throughout Subsystems of a Closed System

I'm studying Landau and Lifshitz's Statistical Physics, Part 1, 3rd edition and am looking for clarification on the following statement, which appears on page 11 in the section on The Significance of ...