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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4answers
601 views

How does the formation of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
1
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0answers
247 views

Calculating heat capacity from the equation of state

It is known that within thermodynamics alone, given the equation of the state of a system, one cannot explicitly determine the heat capacity. What is the mathematical reason for this? Intuitively, it ...
0
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2answers
94 views

Question about Charles' law:

Charles's law says that the volume of a given mass of a gas is directly proportional to its absolute temperature. This means if we increase one, the other one is automatically increased. So the ...
1
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1answer
69 views

Calculation of the differential of the entropy

In this review (for those who wants a precise reference see page 8 eq 21), the Author says that: \begin{equation*} S=-\sum_{i}P\left(i\right)\ln P\left(i\right) \end{equation*} and using the ...
2
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1answer
938 views

Storing kinetic energy instead of potential energy - practically possible?

One of the big problems today considering energy is its storage (e.g. batteries are not that efficient, very expensive and polluting). Energy is classically mostly stored as some kind of potential (in ...
7
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4answers
19k views

How much energy in form of heat does a human body emit?

How much energy in form of heat does a human body emit at rest level?
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2answers
271 views

Does the temperature of water determine how much heat will be removed from air used to evaporate it?

This is a question about evaporative cooling as used in residential evaporative cooling appliances. This type of cooling uses the heat in the ambient outside air to evaporate water and remove the heat ...
8
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2answers
132 views

Can the hot combustion products from a large flame be in “non-local thermal equilibrium”

Question: Does it take some time for the hot combustion products from a flame to reach local thermodynamical equilibrium (i.e. for the energy state populations to follow the Boltzmann distribution)? ...
0
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1answer
98 views

Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate?

Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate? Some time ago I had a discussion about it, and despite none of us knowing ...
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2answers
121 views

Why cannot wood be fully burnt?

Burning wood emits smoke and black. Provided more oxygen or whatever required, can wood be practically burnt fully like petroleum gasses that emits a blue flame and little smoke and little black.
3
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1answer
320 views

Entropy is constant. How to express this equation in terms of pressure and density?

In hydrodynamics of an ideal, non-compressive flow we use 5 variables: pressure $p$, density $\rho$ and velocity field $\mathbf{v}$. So we need 5 equations. Landau's "Hydrodynamics" states that the ...
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3answers
664 views

Why are exothermic reactions easier than endothermic?

If we talk about electric heating then we have simple elements in which we apply electrical energy which gets converted into the kinetic energy of the electrons which heats it up. But while cooling, ...
2
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1answer
144 views

Equation of state not linear in energy or system size [duplicate]

Which of these two equations of state are valid? $$S_1 = L_0 \gamma (\theta E/L_0)^{1/2} - L_0\gamma\left[\frac{1}{2} \left(\frac{L}{L_0}\right)^2 + \frac{L_0}{L} - \frac{3}{2}\right]$$ $$S_2 = L_0 ...
4
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1answer
229 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
0
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1answer
87 views

Air vs. Water attraction of Oxygen Molecules

The air we breathe is made up of nitrogen and oxygen gases. The water in a pond is made of a single hydrogen/oxygen molecule. If it wasn't for the surface tension on top of the water, oxygen molecules ...
5
votes
1answer
347 views

Surface Tension - Lung Alveoli

So, the way I understand this is as follows : The alveoli (pretend they're bubbles) have diameters of the order of microns implying a massive pressure required to inflate them by the Young-Laplace ...
7
votes
3answers
13k views

Is it more efficient to stack two Peltier modules or to set them side by side?

Is it more efficient to stack two Peltier modules or to set them side by side? And why? I have a small box that I want to cool down about 20 K below ambient -- cold, but not below freezing. (I want ...
1
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1answer
127 views

A simple osmosis problem

The following is adapted from a problematic question* asked on the Bio site. I would like to ask it free of those distractions here. If there is anything unduly artificial about the problem please ...
3
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0answers
468 views

Heat transfer from hot water through a copper pipe to oil in a tank

I want to build a geyser attached to a pump with copper tubing running into an oil tank. This is done because the oil solidifies at a temperature below 15 degrees Celsius. I have done a few ...
2
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2answers
206 views

Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?

This question follows on previous work on connections between (other) areas of physics and thermodynamics as in here, here and even here. P. Dirac (an electrical engineer initially) was one of the ...
3
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2answers
560 views

Is quantum uncertainty principle related to thermodynamics?

Would like to ask a question, but first i would like to say Hello Everybody in a way that plays the system, since some geniouses decided that one should not be able to say hello in a question. The ...
0
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2answers
159 views

Can we reach absolute zero one day, and if so, can we measure it?

I was reading this question, and I had this doubt, if we can ever reach absolute zero, how can we measure it? I ask this because as far I know, any measurement could change (increase) the ...
29
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8answers
4k views

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero?

Why is absolute zero considered to be asymptotical? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero? I just do not see why our model must work the way ...
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3answers
870 views

Boltzmann constant--why units aren't joules per degree PER MOLECULE

I didn't think the information I looked at did a very good job of explaining the Boltzmann Constant, kB, but once I did this next simple calculation, it seemed clear that what I didn't understand were ...
7
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3answers
216 views

Are there materials that get softer with temperature decrease?

Could be there material that begins melting/softening when it's temperature is lowered? I would say no, but I've seen enough physics to know that not always life is so easy. Moreover I think I've ...
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2answers
2k views

What's the efficiency of real heat engines?

Real heat engines always have lower efficiency than the Carnot efficiency. I wonder how efficient real engines can be? Can their efficiency get anywhere near the Carnot-limit?
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0answers
457 views

Thermal expansion of two bolts

I have this question asking me about the thermal expansions of two bolts, a steel one, and a brass one. I have the equation: $\ (\delta L/L)/T = \alpha $ I don't understand how I can use this ...
18
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12answers
2k views

Why do turbine engines work?

I know roughly how a turbine engine (let's say a gas turbine producing no jet thrust) is supposed to work: The compressor forces fresh air into a combustion chamber, where it reacts with fuel to ...
3
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3answers
223 views

Does one square centimenter of the sun core really radiate this amount of energy?

I have been thinking that since the core of the sun maintains its temperature at 15 million degrees Kelvin, then every cubic centimeter of this core is receiving a certain amount of energy to keep it ...
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3answers
275 views

Latent heat of condensation

Regarding atmospheric processes, I understand that energy is required to evaporate water by moving molecules further apart i.e. a phase change from liquid to gas. The air then ascends into the ...
2
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1answer
178 views

Which air will give more effective cooling ? Dry or Moist?

Yesterday, I had an innovative idea. I live in India, and in summer season, the temperature can reach up to 45 degree Celsius. We use Split 1.5 Ton AC in our small office. The idea is to put an ...
0
votes
1answer
39 views

Can the thermal energy in an object be aligned, creating a thermal jerk?

Thermal energy is related to the speed at which atoms vibrate, therefor thermal energy is a form of motion. In a stationary object, all of these vibrating atoms 'impact' each other in such a way that ...
10
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1answer
1k views

Principle of Caratheodory and The Second Law of Thermodynamics

Background Constantin Carathéodory formulated thermodynamics on a purely mathematical axiomatic foundation. His statement of the second law is known as the Principle of Carathéodory, which may be ...
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1answer
106 views

Enthalpic Excess - Regular Solution Upon Mixing

My professor, in his handout, says the following about this diagram : For $\beta>+2$ there are two minima and phase separation occurs driven by unfavourable enthalpic interactions. I ...
0
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2answers
213 views

The entropy of the universe in an irreversible cycle [closed]

Suppose we have an ideal gas performing an irreversible cycle composed by: an isothermal transformation at $T_{1}$; an isobaric transformation at $P_{A}$; an isothermal transformation at $T_{2}$; an ...
0
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1answer
100 views

Steady state average of physical quantities

Consider the following Hamiltonian: $$ H = \sum_n \left[\dfrac{p_n^2}{2m_n} + U(x_l) + V(x_{l+1} - x_l) \right], $$ that corresponds to a 1-D system of particles with nearest-neighbor interactions ...
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2answers
1k views

First Order Phase Transition - Heat Capacity

At constant pressure : $\frac{dH}{dT}=C_p $ Hence, why doesn't the graph of $C_p$ against $T$ show two perfectly horizontal lines (with the obvious discontinuity) ? I mean the gradient of $H$ ...
2
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4answers
32k views

Why change in internal energy is zero in isothermal process

In isothermal process $\Delta U =0$. But I am having trouble understanding it. Say we have an ideal gas, and say my temperature is constant but I move the pressure, volume from $(P, V) \to (P-dP, ...
1
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1answer
579 views

Chemical Potential with Pressure at Constant Temperature

The above picture shows how the Gibbs free energy of a solid, liquid and gas vary with pressure. I have found no similar graphs on the internet that match the above. Instead I often find these ...
5
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3answers
84 views

Is there a conveniently small unit of volume for talking about molecules?

When discussing energy transformations on the molecular scale, we usually use electronvolts as the energy unit. This is handy because chemical bond energies are a few electronvolts in magnitude. I ...
4
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4answers
5k views

Wrapping plastic in aluminium foil to protect it from heat

Does it make any sense to wrap the plastic handle of a pan in aluminium foil to protect it from overheating when placing it to the hot oven?
0
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1answer
92 views

Exception to weight of hot vs cold water?

I have seen the various posts regarding the comparison of weight of heated and cold water.But is there any contradiction?I live in really hot conditions and as such tap water literally 'boils' ...
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3answers
294 views

Specific Heat equations - paradox!

We know that enthalpy is $h = u + pv$. Where $u, p, v, h$ are internal energy, pressure, volume, and enthalpy respectively. Now specific heat at constant volume is calculated as $c_v = \frac{\partial ...
2
votes
4answers
312 views

role of entropy in gibbs free energy intuition

I have looked at various derivations of the Gibbs free energy equation and the underlying definition of the gibbs free energy. However I have been unable to attain direct insight/intuition over the ...
3
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1answer
188 views

Why formation of rain is adiabatic?

I recently went through the wikipedia page for Rain. It said that There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling,.... It proceeds as ...
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0answers
44 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
0
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1answer
146 views

How can I calculate the speed at which water evaporates when held at 100 degrees Celsius?

If I have a mixture of some higher bp solvents and water, and I heat it to 100 degrees celcius so that the water in the mixture begins to boil, how can I calculate the rate at which water leaves the ...
3
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1answer
55 views

California “firenados”

There are spectacular rotating towers of fire that can be seen in recent television images of fire in California. In this video, we see that these fire towers can rotate either clockwise or counter ...
3
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1answer
677 views

Flory-Huggins ternary phase diagram with a neutral component

I am searching the literature for the Flory-Huggins phase diagram with the following components : polymer, solvent, and a third component that does not interact with the other components (just entropy ...
0
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1answer
172 views

Chemical potential in terms of temperature and pressure

For part (a), I know how to take the partial derivatives of S to get chemical potential, pressure. But there seems that I still need one equation to correctly express chemical potential in terms of ...