# Tag Info

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We define everything in physics because it's useful. In this case it's useful when a fluid flows in a steady state system adn you want to look and energy flows. If a fluid flows through a box, and has a change in specific enthalpy $\Delta h$, with a flow rate of $\dot m$, then the power transferred to the fluid is $\dot m \, \Delta h$ Sometimes all you know ...

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It doesn't. It's a material priority. Specific heat capacity $c$ is the heat required to raise the temperature of one kilogram of the material by 1 degree: $$c=\frac{dq}{dT}/m$$ It is not a material constant, though, as it depends of the state of the material while heating. Materials at different temperatures, volumes, pressures, etc. have different $c$. ...

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It is possible to change the pressure by increasing the temperature - Pressure-temperature law, also known as Amontons' Law of Pressure-Temperature. The basic idea is in the diagram below: The law states that: The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas's absolute temperature. As the temperature ...

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Aluminum Oxide is a ceramic and comes in bits and pieces, see the production process in the link. How will you make it into a crucible? if not by melting and pouring it into a form? The melting point is 2072C . Generally clays also have to be fired to become stable, enter a phase tightly bound that only melting can destroy, or we would not have clay ...

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Assuming that the bullet flies at Mach 2.0, the temperature at the front of the bullet is about the same as the surrounding air (since at that relatively low Mach number, there is little thinning of the boundary/shock layer to cause aerodynamic heating). I do not know how much heating there is from the gases in the chamber/barrel (it may be significant, but ...

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No, black holes do not violate the 2nd Law of Thermodynamics. Imagine that we want to violate the 2nd Law of Thermodynamics by throwing some volume of ideal gas into a black hole. This would seem to violate the 2nd law because when it is outside the black hole the ideal gas contributes some calculable amount of entropy to the total entropy of the universe. ...

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We note the existence of an irreversible, isothermal thermodynamic process during which the entropy increases which is an explicit counterexample to your claim that The net change in entropy from the system to the surroundings should be 0 if the temperature does not change. Consider a classical ideal gas initially confined by a partition to one half of ...

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Yes, microstates possess individual information, as they are genuine physical objects and not just tools of statistics. Individual microstates may differ in positions and momenta of individual particles, or even in the total energy. The fact that you are treating microstates statistically is simply a tool for simplifying calculations.

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It's the simplest useful case. There are more complicated ones, like when external magnetic/electric field needs to be taken into account, or when multiple chemical species are involved, so there is no single $n$, but several molar numbers $n_1,n_2,...$.

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It was probably just the wind Lakes freeze at their surface because between 0 and 4 degrees C water decreases in density with temperature. That means that the warmer water will sink and the cold water will rise to the surface. This convection will be much faster than any other mode of heat transfer. This means that in the cooling process the water will be ...

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The ideal gas law can be derived from the fundamental differential equation of thermodynamics: First, consider a lattice model with M sites and N particles. Then the multiplicity of the system is: $W = \frac{M!}{N!(M-N)!}$ Thus the entropy of the system $S = klnW = kln(\frac{M!}{N!(M-N)!}).$ Using Stirling's approximation: $n! \approx (\frac{n}{e})^n$ ...

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The dynamic version of equilibrium thermodynamic is fluid dynamics, and the dynamic version of equilibrium statistical mechanics is kinetic theory. In fluid dynamics the stress (pressure) tensor of the gas is expanded in time and space derivatives of the thermodynamic variables. This expansion converges if the state variables vary sufficiently slowly. In ...

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First of all, both pressure and temperature are quantities statistically connected to averages (average force on the wall exerted by the particles and their average energy). So using them in cases, when the system is not homogeneous is not too appropriate. If we want to look at, let's say, gas in the box receiving heat from one side, and see how the ...

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1) These sorts of things are actually being studied nowadays with trapped atomic gases. These gases are released from optical traps and expand into what is essentially a perfect vacuum. If you want, they can be recaptured, although a typical trap does not have sharp walls'', but harmonic confinement. 2) Yes, if you expand into a vacuum then you just ...

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At thermal equilibrium, a blackbody will have no net emission of energy, but that's not the same thing as no emission at all. Obviously, a blackbody will emit blackbody radiation, but at equilibrium it will absorb exactly the same amount of energy. If it emits more than it absorbs, its temperature will fall; if it absorbs more than it emits its temperature ...

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Assuming you mean the enthalpy of combustion, carbon dioxide doesn't combust. That is it does not react with oxygen to produce water and carbon dioxide. Therefore it has no enthalpy of combustion. Did you mean carbon monoxide?

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At the atomic/molecular level all chemical reactions are Quantum Mechanical phenomena where atomic and/or molecular electron orbitals of the reactants are being destroyed and new ones created in the reaction products. This is what you are correctly referring to as formation of bonds (although it has to noted that some bonds are also broken during chemical ...

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Contrary to @Gert 's answer, creation of photons from reactions forming and breaking chemical bonds (typically reactions between molecules) is quite rare. When photons do occur, it can be (1) the result of a molecule, atom, or structure created or altered by the reaction being in an electronically excited state, which then decays, emitting a photon. There ...

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