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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Why different substances have different specific heat capacities? [closed]

Specific heat capacity depends upon the nature of the substance. But i want to know, in what way? Temperature is defined as the average kinetic energy of the molecules. So,for a given mass, a sample ...
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1answer
39 views

Relationship between degrees of freedom and heat capacity and absolute zero?

The Wikipedia article on heat capacity indicates that there is a relationship between the number of degrees of freedom and the heat capacity. I understand this in terms of the equipartition theorem ...
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2answers
56 views

Why do color of metals change when they are heated?

I am a 10th grade student.I have seen that when a metal is heated it's color changes.But I cannot understand how heating a metal changes it's color.
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25 views

What is melting / boiling from the statistical viewpoint?

Microscopically, solids are usually described as "completely ordered" and "strongly bound", liquids "somewhat ordered", and gases "unbound" and "disordered". Thermodynamics predicts that the ...
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1answer
41 views

Why does a magnet loose magnetic strength when heated?

Magnet manufacturing companies, for example Dexter Magnetic Technologies do not hesitate to explain the effects of heat upon magnets - citing how it degenerates the magnetic properties with levels of ...
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2answers
52 views

Gravothermal catastrophe: looking for simple explanation

I am beginning to try to understand the gravothermal catastrophe. I was hoping someone could provide an explanation to help me understand what the gravothermal catastrophe is and why it is important, ...
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1answer
13 views

What are the assumptions made when analysing a stretched elastic string from a thermodynamic aspect?

Consider a stretched elastic string. Then conducting a thermodynamic analysis of the elastic string. The approach is very similar to that used for $(P, V, T)$ systems, with the pressure and volume ...
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1answer
53 views

Radiative equilibrium of a relativistic black body

A black body in empty space in the CMB rest frame should (discounting starlight) come to an equilibrium temperature of around 2.7 K. However, if the body is moving relative to the CMB frame, one side ...
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1answer
35 views

Balloon of ideal gas suddenly pops in the vacuum of space - final average energy per atom?

My question is: is the following thinking pretty much correct? I'm interested hearing about anything here that is fundamentally wrong. Of course there is a bit of hand waving and approximation. If a ...
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11 views

Temperature equalization by radiation between two coaxial cylinders - independent of diameters?

Ignoring end effects, assume I have a cylinder of diameter d0 at controlled temperature k0 and then introduce a smaller diameter cylinder of diameter d1 and temperature k1 to the interior. Does the ...
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2answers
36 views

Mixture of different gases filling their container

If I have a closed container with a mixture of two or more gases $\rho_1$ and $\rho_2$ for instance at thermal equilibrium where $\rho_1>\rho_2$ how would I determine what percentage of the ...
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33 views

How to deduce the modified Flory-Huggins equation in this form?

In the paper of "Solution Properties of Poly(N-isopropylacrylamide)" (M. Heskins and J. E. Guillet, Journal of Macromolecular Science: Part A - Chemistry, Vol. 2, Issue 8, pages 1441-1455, 1968), they ...
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1answer
34 views

Voltage homogeneity across cell membrane

During respiration, individual cells produce a relatively large potential difference ($\sim 100$ mV) between the inside and outside, using energy to pump $H^+$ out of the cell to the liquid ...
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1answer
37 views

Calculation of internal energy and entropy of ideal gas

I am having some trouble with calculation of entropy and internal energy for ideal gas. All sources which provide such derivations which I managed to find either assume a priori that $U$ is some ...
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1answer
32 views

Derivation for the most probable macrostate for distinguishable particles using lagrange's method of undetermined multipliers

We have an expression for $\Omega$ (occupation of each macrostate) in terms of $n_i$ (occupation numbers) . We want to find the $n_i$ which maximises $\Omega$. We now that ...
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26 views

temperature in adiabatic expansion

First, adiabatic means no heat transfer. Second, isothermal means temperature is constant. Is an adiabatic process also isothermal always? I know that an isothermal process is not always adiabatic. ...
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26 views

Efficiency of a Carnot refrigerator without knowledge of the temperatures

We know that in a Carnot refrigerator we can express the efficiency as $$\eta = \dfrac{Q_1}{Q_2-Q_1}=\dfrac{T_1}{T_2-T_1},$$ where $T_1$ and $T_2$ are temperatures of the reservoirs between which ...
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12 views

Partition Function of 1-D oscillator

I was going to find the average K.E and P.E with respect to a oscillator with energy : $$ p^2 /2m + bx^4 $$ I successfully calculate the average K.E using the technique of Gaussian integral and ...
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2answers
74 views

Is it possible to produce higher temperature than the light source with passive device only?

Suppose the light source is a black body with average temperature 2000K, and I want to use it to heat another black body to 2500K, via passive devices only. Here passive device means lens, mirror, ...
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1answer
36 views

Question about reversible heat engine efficiency

I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. ...
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2answers
94 views

Deriving the Ideal Gas Equation

Im specifically looking at how the IGE can be derived from the kinetic theory of gasses. Most textbooks and webpages I've viewed start off with a wall that the particle is hitting and then writes an ...
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1answer
49 views

Cross-differentiation to derive the maxwell relation $\left(\frac{\partial T}{\partial V}\right)_S = -\left(\frac{\partial P}{\partial S}\right)_V$ [closed]

How can I use $T=\left(\frac{\partial E}{\partial S}\right)_V$ and $P=-\left(\frac{\partial E}{\partial V}\right)_S$ to derive $$\left(\frac{\partial T}{\partial V}\right)_S = -\left(\frac{\partial ...
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1answer
72 views

Quantum field theory: zero vs. finite temperature

I have recently been made aware of the concept of thermal field theory, in which the introductory statement for its motivation is that "ordinary" quantum field theory (QFT) is formulated at zero ...
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29 views

Enthalpy in MIT open courseware

I am watching Statistical Mechanics I in MIT open course ware. I have question on one of the lectures and I appreciate it if Mark or someone familiar with this topic can help me. (this is about ...
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14 views

Pressure and temperature in Nozzle

I'm trying to calculate the change in pressure per temperature in a chamber before a nozzle throat, which will choke the flow at M = 1. I have a linear increase in temperature from 300K to 2500K. I ...
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4answers
76 views

Why does heat engine need to reject energy to environment?

The most efficient thermodynamics cycle is the Carnot cycle, it involves 1/ Receiving heat from hot source, expanding and doing work on the surround 2/ Receiving work from environment, being ...
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30 views

Is quantum entanglement related to the thermodynamic equilibrium?

https://www.quantamagazine.org/20140416-times-arrow-traced-to-quantum-source "Today, Lloyd, Popescu and others in their field see the arrow of time differently. In their view, information ...
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2answers
48 views

Pressure exerted by ideal gas on walls of container

All derivations I've come across are more or less similar to this: All of them take total momentum change as $2mv_{x}$ and divide it by total time to get the force exerted on the wall. That seems to ...
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3answers
66 views

A relationship between entropy and temperature

I tried deriving a formula relating entropy (not change in entropy, but entropy itself) to temperature. I’ve only seen two equations really relating to entropy thus far, and only one of them includes ...
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3answers
53 views

What physical properties can't be predicted based on index of refraction? [closed]

If I tell you the real and imaginary parts of the index of refraction for all frequencies, name a property that can't be predicted based on that information. If you're assuming this is a gas, specify ...
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1answer
68 views

Statistical Physics: How do we derive this equation?

I'm reading through Statistical Physics by F. Mandl and there is a step in arriving at an equation that I don't follow. He uses $$P = \sum_r p_r \left(-\frac{\mathrm dE_r}{\mathrm dV} \right) ...
3
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1answer
63 views

What are the phenomena responsible for irreversible increase in entropy?

https://www.quantamagazine.org/20140416-times-arrow-traced-to-quantum-source This article says that entanglement drives the arrow of time of increasing entropy towards thermodynamic equilibrium: ...
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1answer
30 views

Is there a limit to the difference between the boiling and melting points of any material?

Is there a mathematical limit to the difference in the temperatures, a substance acquires before changing states, in this particular case, is there a limit to the difference between the boiling and ...
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20 views

Optimal two-stage warming up of a bottle of baby milk

Here's a common two-stage method to warm up a bottle of baby milk to avoid uneven milk temperature: 1) Heat up a bowl of water in a microwave oven. 2) Put the bottle into the bowl of heated water to ...
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3answers
793 views

Does electricity have an associated entropy?

One can certainly measure entropy changes associated with the generation of electricity, but does electricity itself have an associated entropy (maybe related to voltage, current etc.)?
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2answers
29 views

Calculating the time for two bodies to reach thermodynamic equilibrium

If we have two bodies a and b, with temperatures $T_a$ and $T_b$ respectively, with $T_a > T_b$ and we also know that body b is surrounded by body a completely. How do we calculate the relaxation ...
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1answer
29 views

Dalton's law of additive pressures

In a mixture of ideal gases, if the pressure of the mixture is doubled, what happens to the partial pressure of each gas? Please explain. Thanks a lot. We start with the expression for the pressure ...
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13 views

Can vaporization heat added to the whole volume of liquid before vaporizing it?

It seems, for example a volume of water is heated to boiling point, then part of the water is vaporized, while the remainder need much more heat to vapor, which means that part doesn't receive latent ...
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44 views

How much time it takes to boil water in a rigid body?

I have a question that bothers me. If we have a rigid container containing water at $P_1 = 1$ $atm$ and $T_1 = 25$ $C°$. If we add an electric resistance to heat the water inside, we go through ...
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2answers
70 views

Can first law of thermodynamics be explained in terms of entropy?

Can first law of thermodynamics be explained in terms of entropy? I am bit confused. I need help.
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21 views

Phase diagram binary mixture

The Gibbs Phase Rule states: F = C - P + 2. From this it is possible to construct a phase diagram. In case of a 1-component system C=1 and where P denotes the number of phases in equilibrium. In case ...
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30 views

Explanation of chemical potential

I made a NVT Lennard Jones Monte Carlo simulation. In this simulation I calculate the chemical potential of my system with $$\mu = \mu_{id} + \mu_{ex} $$ Where $\mu_{id}$ is the chemical potential of ...
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1answer
16 views

How to find the temperature difference over a specific plate given temperature difference between two plates?

I'm having trouble solving this question where two metal plates are in thermal contact with each-other. I'm given the type of metals in each plate, the thickness and the overall temperature difference ...
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23 views

Maximum work delivered by a heat engine

I've been solving some Thermodynamics problems and found this one: A thermal machine works between a tank containing a volume $V$ of water and a river at a constant temperature of $T_R$. If the ...
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1answer
25 views

Specific heat capacity for solids of changing temperature

I was reading the following post: If the specific heat capacity depend upon the temperature, what formula we should use instead of $Q=mc\Delta T$ and I understand that the total energy needed is ...
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22 views

Heat transfer with a small airgap - conduction v convection v radiation

I have a transducer approx 25mm dia x 25mm length which will sit inside a brass casing, but stood off from the walls by around 0.5mm. Obviously the brass is a far better conductor than the plastic of ...
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1answer
16 views

Why is the pressure value of an ideal gas for a fixed density and constant temperature of gas more than that of the same real gas?

I solved a question- Under what pressure will carbon dioxide have the density 500g/l at the temperature 300K? Carry out calculations for ideal and Van der Waals. On solving for pressure, I get For ...
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2answers
24 views

Consequences of $T_{sat}$ and $P_{sat}$ dependence

I understand that boiling point increases as pressure increases. This means that if you boil water at higher pressure it is going to need much more energy to break the bonds and thus boil at higher ...
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20 views

Sign convention when proving the equivalence between Clausius principle and the 2nd law

I have a question about sign convention of work and heat in a proof of the equivalence between Clausius principle and the 2nd law. My lecture note brings up a model where two heat engines are combined ...
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24 views

The driving force for first order phase transition

The driving force for the solidfication is said to be the free energy difference, but phase transition actually happens due to change of temperature toward the critical temperature. It seems that ...