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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If I accelerate a mass quickly enough through a short distance (i.e. unit step function), would I create wind, sound, and heat?

As far as I know, the movement of air molecules can result in what we call wind, sound, or heat (and maybe some other things I'm not thinking of), depending on the assumptions about its motion. Wind ...
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1answer
62 views

why doesn't liquid metal vaporize in a vacuum?

I am wondering why molten metal in a vacuum of electron beam and machines never turns to gas like liquid water does when exposed to a vacuum.
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1answer
48 views

Why does the rate of melting of an ice block vary in different methods?

I saw that an ice block melts faster when it is placed in a microwave rather than when it is exposed to flame. Could it be because the flame creates a layer of water vapor between the flame and ice? ...
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46 views

Corrections to the Equipartitio theorem

Does anyone know why sometimes $E = \frac{3}{2}k_{b}T $ is written as $E = \pi k_{b}T$. Where does this come from?
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4answers
219 views

Mass, energy, and entropy.

I have a seemingly simple question about the relation between these three that for some reason doesn't make sense to me. If entropy is the disorder of a system, then a low entropy state is one of ...
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2answers
102 views

Thermodynamics : Work done on gas inside container by the force due to pressure exerted by external atmosphere

Suppose a container is fitted with a massless and frictionless piston lying on a table such that pressure due to gas is greater than pressure due to external atmosphere. Hence piston will move. Now ...
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58 views

(No need of 2nd law) Adiabatic and isothermal compressibility relation with specific heat

One classical example of thermodynamics is the relation between the Adiabatic and Isothermal Compressibility Relation with the Specific Heats: Compressibilities: ...
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33 views

Activation energy as a function of defects

Electrical conductivity has a form of Arrhenius equation. It is assumed that activation energy decreases with defect density in the insulating state and becomes zero in the conducting state. Can one ...
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36 views

Calculating/estimating heat transfer losses for hot air balloon (lantern)

I'm trying to build a flying lantern / hot air balloon that flies as close to hovering as possible (as opposed to up-up and awaaay). To see if this is feasible I'm trying to simulate as much as I can ...
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64 views

Is equilibrum condition consequence of second law of thermodynamics?

Equilibrum state is generally stated to be most stable state. Is equilibrium state consequence of second law of thermodynamics at microscopic level. i.e a system tends to reach the equilibrium state ...
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41 views

Is it possible to tell time within a steady state?

(Inspired from this question (A) which unfortunately the link in the selected answer is now 404 broken (which might have contained my answer), thus cannot read any deeper than that) From the above ...
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12 views

Energy under constant pressure and temp

Conceptual problem: let A + 2B -> C + 2D be a reaction under constant pressure P and temp T, that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the molar enthalpy ...
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53 views

Determination of “Heat transfer coefficient” between block of aluminium and air

I need to build a temperature control system for a hot plate of aluminium, which I intend to heat with an electric cartridge, and the temperature I would be measuring with a PT100 to close the loop. ...
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66 views

Does Expanding Universe conflict with the Thermodynamics 3rd Law? [duplicate]

I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum. Expansion of the universe made a transition from radiation dominated era ...
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1answer
54 views

Efficiency of a real engine

Can anyone tell me what is wrong with the following argument? Consider a Carnot engine and an engine $X$ whose efficiencies are $\eta_c$ and $\eta_x$ respectively. Let us assume that ...
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31 views

An interesting question on the mass of a droplet of liquid experiencing the Leidenfrost Effect

Background and Inspiration: I have seen numerous demonstrations of the leidenfrost effect, both on the internet and in my mother's kitchen. But I started wondering about a general case after having a ...
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52 views

Is the gas constant really a constant?

For ideal gases we have $$ C_p-C_v=R $$ now the left hand side of this equation is temperature dependent, so how is it possible that gas constant $R$ is temperature independent?
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26 views

Is using molar terms with maxwells relations misguided?

My professor wants me to do a lot of derivations using maxwells relations. One of the things he wants me to prove is that from the Van der Waals equation of state one can say: $\Big(\frac{\partial ...
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18 views

Kettle barbecue thermodynamics question

I have an old kettle barbecue which lost its legs to rust. I then placed the dome on top of a truck's brake drum and throttled the airflow by mounting the brake drum on a plate with holes drilled in ...
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30 views

Melting icicles

If I break off the bottom half of an icicle, will the top half melt faster?     ...
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1answer
21 views

Cooling effect of sipping

Is the primary action of cooling of a sipped hot fluid explained by the reduced flow of the hot fluid, the air cooling of the fluid as it is sipped or another factor?
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25 views

Equation of State of PVT system

Find the Equation of State of a fluid with Volume expansivity $\alpha_P$ and an isothermal compresibility $\kappa_T$ are given by $$\alpha_P=\alpha_0 \Big(1-\frac{P}{P_0}\Big) \\ \: \: \: \: ...
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43 views

Isothermal Expansion in Real Gases

I understand that for a ideal gas in the case of reversible isothermal expansion, $\Delta U=0$ and $-Q=W$ but in case of a real or van der Waal gases, how can I find $Q$, $\Delta U$ and $\Delta S$?
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46 views

Dielectric heating - does EM field transfer energy to polar molecules?

In AC field, polar molecule are trying to align with external field. At high freguencies, changes of field are so quict, that molecules cannot align with it. This leads to increasing kinetic energy of ...
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44 views

Pressure, Momentum and Energy: A 'Peculiar' Relation

Is the following possible? $$ P = \frac{p^2}{3E} $$ where $P$ is pressure, $p$ is momentum and $E$ is energy. In what convention is the above relation acceptable? EDIT: The source paper can be found ...
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42 views

Thermodynamics vs Kinetics

As a chemical reaction approaches equilibrium, one of forward or backward reactions dominate the other. According to thermodynamics, this is because the gibbs free energy change for one is negative. ...
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61 views

Entropy and Gibbs Free Energy

I've been struggling with the notion of entropy and gibbs free energy for almost three days now. Different sources on and off the internet say different things about entropy. Gibbs Free Energy is ...
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2answers
112 views

How does a radiometric infrared camera estimate an objects temperature?

Say we have an infrared camera which measures some amount of radiation, in a spectral bandwidth which is given, between wavelength $\lambda_1$ and $\lambda_2$ from a perfect black body. How is it ...
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51 views

Calculating the heat transfer into CO$_2$ gas at a constant pressure

I am having trouble with a homework question and I am just not sure how to attack it. We have not covered how to deal with non-ideal gases yet, and we are expected to answer this question without that ...
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29 views

reflecting foil on window

Assumptions: A house window acts as a cavity resonator, and so can be treated as a blackbody. If the room temperature is 20 C then the outgoing radiation is 418 W/m2 If the outside temperature is ...
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1answer
38 views

Rankine Cycle pressure

I don't understand why in (Ideal) Rankine Cycle we assume that pressure remains constant at the boiler and the condenser. Shouldn't water pressure change, when water goes from liquid to vapor (boiler) ...
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1answer
51 views

Decrease in system pressure do to gas dissolution?

A system of fixed volume contains two fluids as illustrated in the figure below, in equal volumes. Their pressures are both equal and high (much greater than atmospheric pressure). Initially the ...
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45 views

What are the Fermi and Debye temperature constants?

What are the Fermi temperature and Debye temperature constants? We were discussing these in class and I don't fully understand what these constants are or why we have them. Can anyone explain?
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56 views

Ising Model with All Spins Interacting with All Other Spins

I am studying the Ising model with all spins interacting with all other spins and have formulated $Z$. I am trying to understand what it means to study at large N but not infinite N. I know that at ...
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1answer
95 views

Difference between Isothermal and Free Expansion

I just don't get the exact difference between isothermal expansion and free expansion: in free expansion there is no work done since there is no external external pressure. As to the case of ...
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16 views

How numbers of being stretched effects on the internal pressure of a balloon

When you blow a balloon, the shell would become thinner. By according to mulins effect, when a rubber material is stretched, its stress-strain diagram changes and of course also its internal pressure. ...
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16 views

Temperatures reached in arc flashes

Good morning, I have a question regarding the arc flashes. Some papers mention that temperatures of nearly 20000 K can be reached during an arc flash. Could anyone explain how to come up with those ...
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16 views

Trying to determine transient response of air conditioned room

I have an air conditioned room which intakes airflow at temperature $T_{in}$ at a mass flow rate $\dot m$. The air leaks out of the room at mass flow rate $\dot m$ and temperature $T_{room}$. The room ...
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90 views

Partial derivative of Helmholtz free energy from entropy and internal energy

I want to know how to derive pressure $p$ from a partial differential of Helmholtz free energy $F$. I want to start from $F(T, V, N) = U(S(T,V,N),V, N) - TS(T, V, N)$, where $U$ and $V$ are ...
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1answer
61 views

The relation between Internal Pressure and flow rate in a balloon [duplicate]

I'm working on a project. We have two balloons, connected by a hose with a valve.We know when we open the valve, by according to internal pressure of each balloon, air goes form the higher pressure ...
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1answer
59 views

Heat capacity $C$ at low temperature

The internal energy, $U = Nk_bT$ where $N$ is particle number, $k_b$ is Boltzmann constant and $T$ is temperature. Therefore, the heat capacity $C$ is given by $C=\frac{dU}{dT}=k_b$. However, in ...
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Constant volume gas thermometer

Well, in the notes I took in thermodynamics' class I have a graph that plots Pressure of boiling point $P_b$ over Pressure of freezing point $P_f$ at constant volume in terms of Pressure of boiling ...
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56 views

General boundary condition for 1D heat equation

I'm studying from Numerical Solution of Partial Differential Equations by K.W.Morton and D.F.Mayers (Amazon link). I'm confused with general boundary conditions. Could someone give me a clue? For ...
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1answer
50 views

Gas compressed and cooled

If a certain amount of a gas is compressed into a cylinder by the action of a piston that reduces its volume (lets say at a low speed), the kynetic energy of the gas molecules increases, what is ...
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1answer
74 views

Could the uncertainty principle theoretically be violated at 0 K? [duplicate]

Ok so please excuse me if the following mental argument is completely ridiculous or obviously flawed :P I was reading about how, even at 0 K (assuming we could experimentally reach such a ...
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52 views

Calculating saturation mixing ratio for water in air

If I have air pressure (in, say, Pa) and air temperature (in, say, K) - how do I calculate the saturation mixing ratio for water? I can't seem to find it anywhere and it's a fairly useful quantity to ...
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32 views

heat transfer between objects

when we touch a very hot object, the edges of our skin interact with the object's high energy and velocity particles and molecules. why is it physically that we get "burned" by extremely cold objects ...
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30 views

Chemical potential and origin of pressure in a solid

Pressure of a gas is related to the rate of change of momentum of the particles; the temperature is the mean kinetic energy of the particles. Can the chemical potential be given a similar physical ...
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46 views

Partition function for a two state system

We have a system of two energy states and we treat classical distinguishable and indistinguishable particles respectively. For the distinguishable case I thought that all in the left one one left ...
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1answer
38 views

When does exergy destruction occur?

I am doing a project on developing a code for the first and second law analysis of the Brayton Simple and Modified cycles. The first law part is simple. But I have run into a roadblock when I started ...