Questions tagged [thermodynamics]

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

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How can the Gibbs free energy equation be at constant temperature and pressure?

I have read that the equation $\Delta G = \Delta H-T\Delta S$ is valid only at constant temperature and pressure. However, $\Delta H=0$ in an isothermal process which would give $\Delta G = -T\Delta S$...
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Equilibrium entropy definition for fluctuations of the extensive parameters

I am looking for a valid definition/formulation of the equilibrium entropy fluctuations $\Delta S$, with the request that: $$0 \geq \Delta S \hspace{1cm} (1)$$ The fluctuations in the extensive ...
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What is the temperature of an atomic nucleus?

I conjecture that atomic nucleus with $N\approx 250$ particles could be interpreted as a system in equilibrium (maybe the number is too low to consider the use of statistical mechanics as a reasonable ...
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Understanding temperature drop within throttling processes

I am studying a particular throttling process (https://en.m.wikipedia.org/wiki/Isenthalpic_process, https://en.m.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect): cryogenic flow going through an ...
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Q:Number of cylinders and output power [closed]

Please help me to understand why the power in example 9-57 is not same as example 9-158, as $$ {\dot{W}}_{net}={n}_{cyl}{W}_{net}\frac{\dot{n}}{{n}_{rev}}$$ $$ =(4)\cdot (1.502)\cdot (\frac{3500/60}{1}...
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How can the temperature of the surroundings be constant during a reversible thermodynamic process?

I am having trouble reconciling the following statements I have recently learned about thermodynamics: The temperature of the surroundings is taken to be constant (with only infinitesimal changes) ...
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Information-theoretic interpretation of Helmholtz free energy

In The" wake-sleep" algorithm for unsupervised neural networks (GE Hinton, P Dayan, BJ Frey, RM Neal - Science, 1995), the authors gave this interpretation of Helmholtz free energy: $$\begin{...
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How fast does a motorcycle need to go to set fire to the friction marks? [closed]

In movies, you'll see them often use fire on tire friction marks. I propose the question: under what circumstance would this actually happen? What would the RPM of the tires or Speed of the Vehicle be?...
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Is there a steady state for two conductors at different temperatures connected to a battery?

I have not been able to find a general or a specific answer to this question. Let us consider two identical conductors $A$ and $B$, with temperatures $T_A$ and $T_B$, respectively. Let us suppose that ...
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Introductory text to the Boltzmann equation?

I'm searching for a good introductory text to the Boltzmann equation and how it gets applied in the relativistic case as well?
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Amount of water vaporized when cooled down naturally

Suppose we have $m_i$ kg of liquid water at $100 °C$. This water cools down to $20 °C$. We want to estimate roughly the amount of water that would have to evaporate, in adiabatic conditions with the ...
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Why aren't all irreversible processes isobaric?

I am slightly confused about graphs of irreversible processes. Firstly, they are difficult to find and whenever I find them the form is something similar to:- I have read about the explanation given ...
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Showing spontaneous change for mechanical system is described by change in potential being negative

In this PDF by MIT, the condition that mechanical system evolves by the law that the internal change is negative is derived. In the derivation, the assumptions used as the systems are of constant ...
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Building a house that is warm in winter and cool in summer [closed]

The Northern house architecture is strikingly different from that used in the South (I am not taking extreme cases, thinking more of Northern or Germany versus Mediterranean: Thick layers of thermal ...
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Why is this happening to the milk?

I noticed that when the Milk churn was leaking, and there was some milk on its outer surface, whenever I moved the churn, there was a residual extremely thin layer of milk under it, that started to ...
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Could a window mounted wet cloth sheet chill a room?

Assuming there is a light wind, that construction is partly shaded and a constant water pouring and evaporation of the material is occurring due to the breeze.
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Why is thermal noise Gaussian distributed in voltage, but Rayleigh distributed in amplitude?

This is a follow-up to a similar but distinct question I recently asked. Background. Consider an ideal antenna. For ideal polarized thermal noise treated as a sum of random, complex phasors, ...
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My interpretation of kinetic theory of gases predicts empirically false thermal decomposition temperature

I have an intuition that, for 50% thermal decomposition of water gas, the average collision energy must equal the $2H_2 + O_2 \iff 2H_2O$ enthalpy of reaction divided per unit molecule. I have another ...
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Can I always solve a given problem by choosing an open system as well as a closed system?

Consider a room with air and an electric heater inside. I want to determine what will be the temperature of the air in the room after 1 hour of starting the heater (whose power rating is known). The ...
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How can we experimentally confirm that atoms/molecules in a solid actually "move"?

The atoms in a solid are so attracted to each other that they "vibrate" and don't move past each other. How do scientists "measure" that atomic vibration in a solid (let's say at ...
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Thermal noise phasor amplitudes are Rayleigh distributed. How are voltages at the antenna distributed?

Background. Consider an ideal antenna. For ideal polarized thermal noise treated as a random phasor sum, bivariate Gaussian statistics apply to the resultant phasor (call it $\vec{v}$) that is ...
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Problem concerning heat capacity of an ideal bose gas [closed]

I have a problem with problem 18.4 From Huang (Introduction To Statistical Physics). Could anyone help me to understand how the second derivative of lnz with respect to t is computed? At the end of ...
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How can mechanical equilibrium be guaranteed in adiabatic expansion? [closed]

Assuming I have a perfectly thermally insulated metal piston in my hand. I reach for the piston, pull on it and let go again- nothing moves. What happened to the gas in my system: T down, p down, V up....
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How does an exothermic reaction release energy? [closed]

When a reaction is exothermic it releases energy often denoted in kJ/mol. This is due to the total enthalpy of the reactant(s) being higher than the enthalpy of the product(s) and thus needs to ...
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How do I create an experiment for measuring the effect concentration of salt has on water's specific heat capacity?

I am trying to create an experiment that is trying to show this. Originally, I thought of using a calorimeter and thermometer, and boiling water to 100 degrees Celsius, and then put the water in the ...
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Solving an inexact differential

So we have something called an inexact differential which is when a function is path dependent meaning I can't just subtract the initial and final states to get an answer. Take for example work which ...
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Unable to derive Grand Canonical Free energy for single electron transistor (SET)

I am try to derive the expression for Grand canonical free energy for single electron transistor (SET) and started with a simpler case as shown below from Physics of Nanoelectronics by Tero Heikkila: ...
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Steel is generally not used directly after quenching, but is then tempered,tempering is generally not used alone. what are special circumstances? [closed]

The steel is generally not used directly after quenching but is then tempered Tempering is generally not used alone. what are the special circumstances? Or Under what circumstances should the steel ...
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Does taking the $\log$ of a quantity change the unit of the quantity?

\begin{align} &= c [P - b \ln(P+b)]_1^{500} \\ &= 0.125 \frac{\text{cm}^3}{\text{g}} \times \left[\begin{aligned}&500 \text{ bar} - 2700 \text{ bar} \times \ln(500 \text{ bar} + 2700 \text{...
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Why does adiabatic expansion occur in the carnot process?

(Spoiler: Why adiabatic expansion happens in Carnot cycle doesn't really answer the question for me.) In the Carno cycle, the open system is first brought into contact with the warm reservoir, which ...
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A cup is able to hold 500ml of water. I want to pour boiling water into it such that it cools faster [closed]

A cup can hold 500ml. I have 1 liter of water at 100°C If I put 500ml onto the cup the water will take much longer to cool down. If put 50ml of cup every 10 minutes will the water take much faster to ...
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Gibbs free energy of mixing with respect to temperature, is there a relation with lagrangian formulation of mechanics?

The Gibbs free energy determins if two substances are miscible at certain temperature since it will get minimized: $$ \Delta G = \Delta H - T \Delta S$$ Where $ \Delta G < 0$ determines if a ...
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Thermodynamics joule’s law [closed]

Is the earth cooling or heating? According to joule 2nd law the earth is cooling for long term as we can prove the heat exchange is negative. What do u think?
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Could a heated coil with a sail to catch the hot air,(in theory) produce enough or any thrust to lift a drone? in the way a hot air balloon works

This is an approach I am thinking of for an alternative to ion propulsion for making silent drones.
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Problem solving (numerically) the Tolman-Oppenheimer-Volkov (TOV) equations for any equation of state [closed]

I've been working on a code to solve the TOV equations for a while and recently I've got it right but only for one specific equation of state, the bag model, wich is not what I need since it should ...
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2 votes
2 answers
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Do Stochastic Differential Equation models conserve energy?

I have recently started looking into stochastic models of chemical reaction systems, particularly the Chemical Langevin Equation (CLE) SDE model (e.g. here). One thing I'm trying to understand is ...
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Do we need atomic theory to do thermodynamics?

With thermodynamics, systems are studied using macroscopic variables (pressure, temperature, volume, etc.) which do not need a mechanical explanation, which is what statistical mechanics deals with. ...
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(Discrepancy in the) Statement of Eigenstate thermalization hypothesis

I am trying to understand ETH and unfortunately came across a seemingly contradicting definition by the same author (Mark Srednicki). I don't know which definition is correct. At this instance in this ...
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$\int \frac{dQ}{T} = 0$ from Carnot cycle

I'm going through a physics book and got to a part where starting from $$\frac{Q_1}{T_1} - \frac{Q_2}{T_2} = 0$$ for $T_1 > T_2$, the authors say that we can rewrite this as $$\sum \frac{Q}{T} = 0$$...
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Galileo thermometer [closed]

Is it true that the clear fluid in the tube is ethanol? And that the weights attached to the glass bubbles are gold?
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Why inversion temperature does not matter for work-producing expansion system?

I was reading about cryogenics in the Perry's 8th Ed. when I stumbled upon this paragraph and I can't wrap my head around the fact that inversion temperature does not matter if you have a work-...
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Determining the Boyle temperature (non-numerical) [closed]

I have been given the following equation of state (in relation to ideal gas laws): $$PV_{m} = RT \left( \ 1+\frac{8}{57}\left(\frac{P}{P_{c}}\right)\left(\frac{T}{T_{c}}\right)\left[1-4\left(\frac{T_{...
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Why does hot water shoot out of my reusable coffee cup when I invert it during cleaning?

In an effort to keep my reusable coffee cup clean, before washing it I rinse it out and half fill it with near-boiling hot water (from an instant hot water tap at work), and invert it aimed at the ...
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Einstein solid multiplicity

I have a question about the multiplicity of an Einstein solid and the probability. I have the book An introduction to thermal physics by Schroeder. It says all accessible microstates are equally ...
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Explaining internal energy from a macroscopic perspective

This question stems from the accepted answer to this question Classical thermodynamics deals with and relates macroscopic quantities, like pressure, temperature, mass, volume, etc. These are the ...
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Can you derive the boltzmann factor from $$ \frac{ \partial P(\epsilon_i)}{\partial\epsilon_i} = -P(\epsilon_i) $$

If you solve the following simple differential equation: $$ \frac{ \partial P(\epsilon_i)}{\partial\epsilon_i} = -P(\epsilon_i) $$ You get: $$ P(\epsilon_i) = c_1 e^{-\epsilon_i } $$ where we ...
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Why do Greenhouse Gases absorb heavily in certain wavelengths?

What molecular properties make greenhouse gases absorb and reemit primarily IR radiation? That is, why are CO2, H2O and NO2 all greenhouse gases (GHGs), but others (such as helium and neon) aren't? ...
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Energy transfer by heat is dependent on the process path, does $Q=mc\Delta T$ says otherwise?

Consider a gas that goes from a state 1 ($P_1, V_1, T_1$) to state 2 ($P_2, V_2, T_2$) by a process path A during which energy was transferred by heat (say 20kJ). The heat transfer to the gas will be $...
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Combustion test of gases for boiler use [closed]

How to mix to gases in specific proportions (e.g. 25 per cent hydrogen and 75 per cent hydrogen)? Thanks in advance I researched using various research papers and texts but nowhere I could find the ...
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Gravitational path integral derivation of black hole temperature and entropy

Using the gravitational path integral we can define the partition function as: $$ Z(\beta) = \int\mathcal{D}g\mathcal{D}\phi e^{-I_E[g,\phi]} $$ with boundary conditions: $$ t_E \sim t_E + \beta, \...
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