All Questions
Tagged with enthalpy or thermodynamics
15,736 questions
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Is Diffusion Theoretically Proven to Be a Markovian Process, or Is It Just a Simplification?
I don't come from a physics background, but I'm curious—Is the diffusion process inherently and theoretically Markovian? Has this been mathematically proven or demonstrated through experiments, or is ...
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Does the behaviour at triple point violate the laws of thermodynamics?
Thermodynamics postulates that if we have an isolated collection of matter, then given enough time, it will reach a state of thermodynamic equilibrium, and so we will not observe any macroscopic ...
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How do I calculate nozzle flow with chemical kinetics?
I found Krieger's 1951 paper titled "Chemical Kinetics and Rocket Nozzle Design" in which he derives the following differential equation for the rate of formation of atomic hydrogen in the ...
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How is radiation emitted from a small hole in a box, if the hole is small enough to prevent radiation from escaping in the first place?
So I totally understand how a hole in a box works as a good approximation for a perfect absorber of all incident radiation (a black body). However, a black body is also a perfect emitter of radiation ...
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If I vibrate an object at a high enough frequency, is it "hot"? [duplicate]
Let's take a (10cm)³ cube of steel as our reference object.
Heat is just atoms vibrating within our cube of steel. Apply more heat, get more vibration; the two are the same.
If we have a good enough ...
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Deriving the general energy balance equation of an open system from Reynold's Transport Theorem applied for energy
The general energy balance equation for open systems is as follows:
$$\frac{\mathrm{d}(mu)_{cv}}{\mathrm{d}t} + \Delta \left(u + \frac{1}{2} v^2 + gz\right)\dot{m}_{fs} = \dot Q + \dot W,$$
and the ...
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Van der Waals for Two Chemical Species
I have a system of chemical species undergoing several reactions very very near the equilibrium, their total concentrations change as you would expect in some sort of clock reaction. My first attempt ...
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Can hot or cold be defined in an isothermal universe?
Suppose there exists a universe which is exactly isothermal. Can we define hot or cold in such a universe? I guess not. No matter what the temperature is, we cannot define hot or cold. Am I correct?
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Perfect gas relation in differential form [closed]
I have a problem to understand the transformation of the perfect gas relation:
$$ \rho\cdot R\cdot T = P $$
into its differential form:
$$\frac {dp}{p} = \frac {d{\rho}}{\rho} + \frac {d{T}}{T}$$
How ...
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Thermal expansion of solid rod
Let us assume a rod is lying on a rough surface. Now, if temperature is raised it will expand, leading to negative work of friction. But there is no change in kinetic energy of rod, i.e. $\Delta E_{\...
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Why does not Earth radiate more energy into the space while it gets warmer? [closed]
The earth is getting warmer. By Stephan's law, it should radiate more energy into the universe.
On the other hand, the energy from the sun is a constant. So how to achieve a balance?
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Are Equations of State purely non-gravitational quantities?
An equation of state relate the pressure to the energy density, $p=p(\rho)$, for a gas, plasma, etc., of particles, and it is the central quantity that characterizes the bulk thermodynamics of matter. ...
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What is the upper bound for black hole entropy derived from in the Bekenstein bound?
From several unrelated sources (such as Scott Aaronson's discussion of hypercomputation or this article about a bound on the number of degrees of freedom of any theory with a positive cosmological ...
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Is a non-cyclic device (i.e. a process) which transfers heat from low to high temperature without work input possible?
The Clausius Statement: "It is impossible to construct a device that OPERATES IN A CYCLE and produces no effect other than the transfer of heat from a heat source to sink". So, is a non-...
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Why are metastable crossover times equal to the exponential of the free energy barrier?
Many different models in stastical mechanics (for example, Curie-Weiss models) share the property that the (expected value of the) time it takes the system to move from one local minimum of the free ...
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Why thermodynamic equilibrium and pressure balance is considered for having a reversible process? [duplicate]
When we compare the rapid expansion of an ideal gas to a very slow expansion from an initial state to a final state, we categorize one as irreversible and the other as reversible. This distinction ...
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Simplified scenario: evaporative cooling vs convective heating between water and air
While thinking through this question I thought of a simplified scenario that would model one of the extremes:
A body of water with mass $M_W$, temperature $T_W$, and surface area $S_W$ is surrounded ...
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Carnot efficiency for IC engine
Consider
$$e= \frac{T_h-T_c}{T_h}.$$
What is $T_c$ in Carnot efficiency for internal combustion engine, atmosphere or exhaust temperature?
If $T_c$ is atmosphere temperature, does that mean engine is ...
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Is $T(V, P)$ a valid state equation for an ideal gas?
If I consider an ideal gas with constant number of particles, I can easily think an experiment where I can control $(V, T)$ or $(P, T)$ independently (state variables). But I cannot imagine an ...
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If a two-state system with $N >> 1$ has zero energy, can it still access any possible microstate?
I understand that the number of microstates in a two-state system is $W = 2^N$. However, if the energy of the system is fixed at zero (for example, exactly half of a paramagnet's N dipoles point up ...
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Does blowing hot air through cooler water, heat or cool the water?
Inspiration for this question was a discussion about hot tubs in desert locations.
Supposed we have a mass of water with a temperature of 90°F. What is the effect on the temperature of the water of ...
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Advection equation of heat transfer during fluid flow in pipe with heat loss
I am trying to model transient temperature profile during fluid flow in pipe considering heat exchange with the surrounding. I am trying to use overall heat transfer coefficient to model heat exchange ...
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Joule expansion: Experimental evidence for temperature change
In his original experiment, Joule found that there was no change in temperature after releasing air from one volume into a larger one [1]. However, we know now that for real gases there should be ...
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Matter made of neutral charges does not radiate?
We know that any blackbody that has a certain non-zero temperature radiates. This happens due to the jiggling of charged particles (protons and electrons), and accelerated charges create ...
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Thermodynamics: complete vaporization of liquid via isenthalpic expansion
I am trying formulate an equation for enthalpy involving an isenthalpic throttle valve that completely vaporizes a liquid.
Here is what I have so far:
$\int_{T_1}^{T_{sat-vap}} c_{p,liq}(T)dT + h_{vap}...
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Confused about empty plastic bottle in the freezer situation
Note: When I say the bottle is "empty", take it to mean, "with just air inside", as we use in everyday life! :)
My question: Suppose we put an "empty" closed common ...
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Definition of Statistical/Thermodynamic Equilibrium
Suppose we have some system $A$ coupled with a reservoir $R$ where $A$ can exchange energy with $R$ but not particles or volume. The system $A$ will have some (time) average energy $U= \langle E \...
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Why Gifford-Mcmahon cycle's Refrigeration Effect is $Q=V(P_1-P_2)$?
This extract is from Advances in Cryogenic Engineering (Vol 11). They do give an explanation for my question in Volume 6, but I am struggling to understand that
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How do electronegativity triggered interactions in redox reactions translate to molecular motion (heat)?
In a Redox reaction, a valence electron is transferred/shared from one atom to another. The Electronegativity of the atom will dictate its tendency to attract shared electrons.
More specifically for ...
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Structure of a quantity which is conserved under collision processes
In a book about statistical physics it is stated, that for each quantity which is conserved under elastic collisions,
$$\Psi(\vec v_1)+\Psi(\vec v_2)= \Psi(\vec v_1') + \Psi(\vec v_2')$$ there is only ...
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Considerations for phase change through throttle valve
I am looking at characterizing, as well as I can, the exit velocity and density downstream of an isenthalpic throttle valve as a function of the downstream pressure. What is throwing me off is the ...
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How much does the Gibbs state differ from the ground state at low tempratures
If we take the Gibbs state $\rho _G = e^{-\beta H}/Z$, at very low tempratures $\beta \to \infty$, then we get the ground state. I understand this comes up because only the first term survives in the ...
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In an Otto cycle engine, why not have the crankcase in a vaccuum?
In a 4-stroke engine, it is extremely difficult to have high efficiency because the hot gases are not allowed to expand until they are atmospheric pressure. But what if they weren't expanding against ...
user431618
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The development of Clausius Inequality
The reversible cyclic device absorbs $\delta Q_R$ from the thermal reservoir at $T_R$ and rejects heat $\delta Q$ to the piston-cylinder device, whose temperature at that part of the boundary is $T$ (...
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Force in thermodynamic configuration space
Consider a thermodynamic system whose internal energy $U$ may not be conserved in general. It's a direct consequence of the First Principle that the variations in internal energy do not depend on the ...
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On The Existence of The Single-Valued Entropy *Function* Via Caratheodory's Adiabatic Inaccessibility
I am looking for an explanation why the impossible example of a thermodynamic systemm see $^{[\mathbf 1]}$, or its obvious generalization that is to follow below, is not allowed by Caratheodory's ...
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Help me to understand why we have $pV$ in the enthalpy equation
I'm learning (slowly) about enthalpy. My understanding is that enthalpy is the sum of internal energy and the work done on the environment, in order to occupy a volume $V$ at pressure $p$?
$$H = U + ...
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Water at zero degrees Celsius: proportions of liquid vs ice?
Suppose I put water on a dish, and I put it in contact with a heat bath whose temperature is zero degrees Celsius. I have two questions:
Given enough time, will the proportions of liquid water vs ice ...
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Is absolute zero an arbitrary number or would an alien civilization agree it is -273.1° C? [closed]
Can absolute zero be calculated from pure mathematics or does it depend on definitions (such as the boiling point of water and freezing point) and experimentally derived values?
user429115
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What is the reason for the presence of phases in materials?
Why is it that the physics of the iron-carbon solid solution system supports such a variety of different microstructures each with different iron-carbon ratios?
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Maximum decrease in entropy per unit of energy?
They say we can decrease the entropy of a system by doing work. For example, this online physics text states, near Eq. 15.6.26, that: "If I pick up marbles that are scattered about the room and ...
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Universe: Isolated or not? [duplicate]
Yesterday in our class, we were taught that an isolated system has the following boundaries: Non movable, adiabatic, impermeable. We were told that the universe can be considered an isolated system. ...
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Can temperature of a body be increased without heating it? Is the converse true? [duplicate]
How can we change temperature without adding or removing heat? Are other form of energies added to the body to increase it's temperature?
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How is Brayton cycle heat injection isobaric?
I'm trying to analyze a gaseous working fluid at the exit of the heating chamber as it heads to a nozzle in a Brayton cycle. My understanding is that the injection of heat creates a rise in internal-...
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Understanding Thermal Expansion in a Bimetallic Strip: Do Different Parts of the Same Metal Expand Differently?
If a bimetallic strip is made by tightly joining two metals (one red and one blue), and the blue metal has a higher coefficient of linear expansion than the red metal, the strip will curl when heated, ...
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Universal equation of state for fluids and gases
I would like to ask, is there any universal equation of state that holds for any and all classical fluids and gases, derived purely from first principles (though constants in it should be measurable, ...
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Why should the Boltmann distribution maximize entropy with average energy constrained?
In statistical mechanics, when working with the canonical ensemble (e.g. a system able to exchange energy with a large thermostat at temperature $T$, the system together with the thermostat being ...
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Einstein Relation; Equilibrium State of a Diffusive system
Consider the convection-diffusion equation with no sources/sinks:
$$\frac{\partial c}{\partial t} = \mathbf{\nabla} \cdot (D \mathbf{\nabla} c - \mathbf{v} c)$$
Where $c$ is the concentration of the ...
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Why is the entropy change for a system in irreversible transformations the same as in reversible transformations in some cases, not in other cases?
Generally, the entropy change for a closed system for an irreversible transformation is not the same in a closed system for a reversible transformation.
A clear counterexample is that of an adiabatic ...
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What is actually temperature in case of solids and liquids?
We know that temperature in case of ideal gases is caused due to the translational component of the velocity, which causes pressure and then we define temperature according to $pV=nRT$.
But for solids ...
