# What is Thermodynamcics: Definition and 53 Discussions

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1. ### How to Calculate the Molar Entropy of H2O(g) at 25°C and 1 bar?

Hi everyone! It's about the following task: Calculate the molar entropy of H2O(g) at 25°C and 1 bar. θrot = 40.1, 20.9K, 13.4K θvib=5360K, 5160K, 2290K g0,el = 1 Note for translational part: ln(x!) = x lnx - x Can you explain me how to calculate this problem?
2. ### What is the change in internal energy after two processes?

So the question goes like this: find change in internal energy in process 1->2 using diagram. And offered solutions a)-400J b)400J c)600J d)800J. First I found T1 and T2 using (P*V)/T=R and got T1=24K and T2=72K. Then I found n(number of moles) using PV=nRT and got n1=1mol, n2=1mol. Then I...
3. ### I Thermodynamic constant -- misunderstanding

I was reading about thermodynamics in my textbook wheni came across the following thermodynamics constants: However, i don't understand why did we define 1/V inthe constants. What is the point in doing this?
4. ### Heat Exchanger: +40C rise at 16 liters/minute flow rate

Summary:: How to calculate the rate of heat transfer between hot external water and cold internal water in a pipe. The image attached is my attempt at the question however, I find myself stuck trying to work out internal and external heat transfer coefficient.
5. ### Understanding basic statistical mechanics formulas

Firstly, I would like to check my understanding of the first formula: Using velocity distribution = f(v), speed distribution = fs(v): fs(v) = f(vx)f(vy)f(vz)dxdydz, since dxdydz = 4pi*v^2*dv, fs(v) = 4piv^2f(v) The second formula is the confusing one: What does it mean? What is the...
6. ### Other Textbook Recommendations for Thermodynamics

Hello there, Can anybody recommend me a good thermodynamics textbook? I prefer the ones that have a deep or complete (if possible) discussion about the theoretical aspect of thermodynamics, and the mathematical aspect as well. Thank you
7. ### Finding the efficiency of an ideal gas with adiabatic exponent 'γ'

Here is what I did : work done in going from A to C, W1 = 2nRToln(2) (isothermal process) work done in going from C to B, W1 = pΔV = nRΔT = -nRTo (isobaric process) work done in going from B to A, W3 = 0 (isochoric process) so, total work done = W1 + W2 + W3...
8. ### Thermodynamic equilibrium with fixed energy/entropy

If you take a system with fixed entropy S0 and let it evolve, it reachs equilibrium. Let Ueq be the energy of the system at equilibrium. Now take the same system with fixed energy U=Ueq (S is not fixed anymore), how do you know that the equilibrium reached is the same as before, that means with...
9. ### Derivation of the change of air pressure with height

If we take a slab of air with cross-sectional area of A and height dz in our atmosphere. Now, what we do is make an argument like this :- Pressure from below must balance both the weight and Pressure from above to keep the slab at rest. ( I have added an attachment for clarification) And...
10. ### Why doesn't Q=0 instead of Q=W if T=constant in first law?

My understanding of heat is the energy transferred as a result of temperature imbalance between systems. If two systems at different temperatures are in contact with each other, a temperature change for both systems and an energy transfer Q is occurring. It is known that Q=W for a closed...
11. ### Variation of energy but constant entropy

Hello; If a system receives a thermal energy Q, can it keep its entropy constant (that is, with equal value before it receives the energy) without wasting the energy received?
12. ### Energy of a crystal in thermal equilibrium

Homework Statement In a monatomic crystalline solid each atom can occupy either a regular lattice site or an interstitial site. The energy of an atom at an interstitial site exceeds the energy of an atom at a lattice site by an amount ε. Assume that the number of interstitial sites equals the...
13. ### I Gibbs Energy Confusion: Proving dG≤0 Constant T,P

By Clausius' inequality δq - TdS ≤ 0. For a constant T,P process in a closed system and no non-expansion work my text states that dG = dH - TdS = δq - TdS ≤ 0 but this seems incorrect to me. If pressure is constant such that dH = δq, doesn't this mean that δq = δqrev since dH is a state function...
14. ### Change of Temperature from Work in Hydrostatic System

Hi, I have a little conceptual question. I have an idea about the topic, but I would need to formalize it a little bit. The problem is the following: Imagine the following scenario: You put a little bit of water in a bottle, you assure yourself that everything as at a constant temperature and...
15. ### Calculating Power Output of a p-V Engine

Homework Statement Homework EquationsThe Attempt at a Solution P = 1500 * [area occupied by the cycle = ## 4 p_0 V_0 ## ] /60 = 15 kW Is this correct?
16. D

### Thermodynamics: box with a moving wall

I have a doubt regarding the answer, a box separated by a movable wall has two compartments filled by a monotonic gas .Initially the volumes are equal but the pressure are 3P and P respectively .When the wall is allowed to move the final pressure is...
17. ### Solid-liquid Equilibrium via EOS

Hi guys I want to model the adsorption of asphaltenes on nanoparticles from a thermodynamic equilibrium solution ( this is my thesis ). from this way, I want to show how much asphaltene is adsorbed on nanoparticles at different temperatures and pressures (without using of isotherms of...
18. I

### Calculating Changes in Internal Energy for a Rising Air Parcel

Homework Statement A 1 kg parcel of dry air initially at a temperature of 15 Celsius (288 K) rises from ground level to its equilibrium height, which corresponds to a pressure of 750 hPa. What is the decrease in internal energy?What is the temperature of the air parcel at its equilibrium...
19. ### Minimum work needed to compensate for a heat leak

Homework Statement A great deal of effort has been expended to find “high temperature superconductors”: materials that are superconductors at temperatures higher than the boiling point of liquid nitrogen (77 K). Most of the older superconductors had to be operated with liquid helium (boiling...
20. H

### How to Calculate Ideal Gas State Properties Using Molecular Dynamics?

Dear all, I want to calculate thermodynamical properties of my molecule which I am calculating its thermodynamical properties of non-ideal part using Molecular dynamics. I need ideal gas state total energy, Cp, and Cv in several different temperatures. I am using opt+freq at B3lyp/6-311++G(d,p)...
21. E

### Thermodynamics: Water Properties

Homework Statement Two pans filled with water. Water in a 3.7cm deep pan is observed to boil at 98 degrees Celcius. At what temperature will the water in a 46.3cm deep pan boil? Homework Equations P=3.146T-211.87 (linear approximation) Water properties table: 95°C 84.609kPa .001060 vf 1.9808vg...
22. ### Internal energy of an ideal gas as a function of temperature

Homework Statement Two containers hold an ideal gas at the same temperature and pressure. Both containers hold the same type of gas but container B has twice the volume of container A. The internal energy of the gas in container B is (a) twice that for container A (b) the same as that for...
23. ### Solving Heat Transfer Problem with Melting Ice Cube

Good day members of physics forums . I am a university student currently studying thermodynamics and I just am a bit confused about a heat transfer problem. If you have the following items: 1 metal container which is well insulated from the outside ; ; 1 quantity of water and an icecube ...
24. M

### 2 body engine, final equilibrium temperate and work produced

Homework Statement 2 bodies with contant heat capacity C and 2C, are initially at temp T and 2T. if a heat engine executing a reversible carnot cycle operates between the two bodies until their temperatures are equal, what is the final temp of the bodies and how much work is preformed by the...
25. ### What was the initial temperature of the lead bullet before it melted completely?

Homework Statement A lead bullet flies at a speed of 450 m / s and, striking a wall perpendicularly, melts completely. What was the bullet temperature before the blow, if for melting it consumes only half of its mechanical energy? Latent melting heat and the specific and melting temperature of...
26. ### How can we best describe entropy other than with disorder?

Entropy is often represented as a representation of disorder in a system or the amount of energy deposited as unusable in a system. What are the other perspectives about entropy?
27. ### Does Building Construction Defy the Second Law of Thermodynamics?

From what I know, the law says that disorder increases over time. But, when a building is constructed the disordered bricks,cement etc. take form of the ordered building. Am I wrong or is this an exception?
28. ### Heat transfer. Could anyone explain the solution?

Homework Statement Homework Equations The Attempt at a Solution This is a solved question. The answer is given above. I can't understand why h1=h2. [/B]
29. ### Proving Carnot efficiency is maximum and conditions

The standard proof to show carnot efficiency cannot be exceeded is to couple a supposedly more efficient engine to a carnot refrigerator, and show that it would violate second law. However, isn't it true that we can make the same argument with any arbitrary efficiency? Some discussions on...
30. ### Diffusion of energy by heat flow

Homework Statement This problem belongs to the Intermediate Physics for Medicine and Biology, Hobbie Chapter 4. The heat flow equation in one dimension $$j_H=-\kappa \partial_x T$$ where ## \kappa ## is the termal conductivity in ## Wm^{-1}K^{-1}##. One often finds an equation for the...
31. ### Leidenfrost effect at thermodynamic equilibrium

Homework Statement A spherical drop of a pure substance floats on top of the vapor of the same substance so the system vapor+drop is isolated. The drop has a surface tension σ. Show that at the thermodynamic equilibrium PL≠PV and calculate the difference. Homework Equations Three laws of...
32. ### Range in solid surface for liquid-liquid phase separation

I am investigating the nucleation on solid surface during liquid-liquid phase separation, I know the free energy change is and I don't know if it is correct to get Can someone calculate it to have a check?
33. ### Understanding the Different Forms of the Ideal Gas Law and Their Applications

Hey I was hoping someone could be me a succinct method of knowing what form of the Ideal gas law I need to use and in particular the different R's associated with each form. Form my Thermodynamics class we use PV = nRT Pv = RT PV = mRT Little v being the specific volume (which changes the R...
34. ### Thermodynamics Compressibility Factor

Homework Statement Please consider ethylene at 152oF and 126 atm. Please determine the molar volume (ft3/lbmole) if Z is determined by Corresponding States Theory. Homework Equations Z=PVm/RmT Vm= Molar volume R=Rm/M M= molecular weight Rm=1545(ft*lbf)/(lbmol*oR) Zc=(Pcvc)/(R*Tc) Tc=283 K...
35. ### Heating Water with vapor at certain pressure

Homework Statement We wish to heat water from 10 °C to 50 °C using vapor at 180 °C and 1.5 bar of pressure. How much cold water do we need to mix with every Kg of vapor to obtain the result? Homework Equations I am not sure. I think the problem is related with exergy and energy balance The...
36. ### Insulated bulbs immersed in heat reserviors

Homework Statement Two glass bulbs of equal volume are connected by a narrow tube and are filled with a gas at ##0^{\circ}C## and a pressure of ##76\text{ cm}## of mercury. One of the bulbs is then placed in melting ice and the other is placed in water at ##62^{\circ}C##. What is the new value...
37. ### Angular Frequency of a Piston with Ideal Gas

Homework Statement A frictionless piston of mass m is a precise fit in the vertical cylindrical neck of a large container of volume V. The container is filled with an ideal gas and there is a vacuum above the piston. The cross-sectional area of the neck is A. Assuming that the pressure and...
38. ### Fluid Flow Loss Analysis Using Real Gas Properties

I am trying to model fluid flow and losses through a component (e.g., pipe) using REAL GAS properties since 1) I have access to RefProp from NIST, and 2) I am dealing with refrigerants, which are far from ideal. I have seen nowhere an analysis of fluid flow losses (e.g., drag, friction...
39. ### How to calculate time to change the temperature of metal

So I'm looking to calculate the time required to raise the temperature of a piece of lead. What I know so far: Mass of metal: 4 grams Initial temperature: 250 degrees Celsius Final temperature: 350 degrees Celsius Specific heat of lead: 0.13 kj/kg I'm very new to thermodynamics and don't know if...
40. ### Why does the entropy increase in free expansion of an ideal gas?

I learned that $$dS = \frac Q T$$ In free expansion of Ideal gas, it is obvious that Q = 0. However, the entropy increases. I guess the reason is that it is because the process is not quasistatic. If I am right, why is this process not quasistatic. If I am not, what's wrong with the formula...
41. ### B Why Does PΔV = nRΔT Hold True in Some Isobaric Processes but Not Others?

In a isobaric process W=PΔV I Given the change in temperature and pressure is constant to find heat added to an mono-atomic ideal gas we use Q=ΔU + W = 3/2 nRΔT + PΔV = 3/2 nRΔT + nRΔT so Q=5/2 nRΔT correct? II But given the heat added to an ideal gas, constant pressure that acts on the...
42. ### B How can a permeable piston be adiabatic?

How can a permeable piston be adiabatic? If substances can go in and out of the cylinder and the substances have heat energy, heat can be exchanged through a permeable piston. I came across this term in the book, but cannot understand.
43. ### Change in entropy of a resistor

Homework Statement Consider a thermally insulated resistor with resistance R=20 Ω and mass m=5.0 g. The resistor is made of a material with specific heat capacity c=850 J/(g-K) and carries a current of 2.0 A for a time period of 1.0 s. a) Calculate the increase in the temperature of the...
44. ### Quantification of Entropy and the 2nd Law of Thermodynamics

All of my information comes from my current chemistry class, I just want to know where I either may have misread, misinterpreted, or was mistold information. With the 2nd Law of Thermodynamics we can say [1]\space\space \Delta{S}_{universe} = \Delta{S}_{surroundings} + \Delta{S}_{system} >...
45. ### I Can You Explain: Why Is It One Sec?

can you help me with this, please?
46. ### How do calculate the prob of being in a state in therm eq?

Homework Statement A pore has three configurations with the energy levels shown. The pore is in thermal equilibrium with the surroundings at temperature T . Find the probabilities ##p_1##, ##p_2##, ##p_3## of being in each level. Each level has only one microstate associated with it. Also...
47. ### Heat transferred into a closed system

So i am making a simple demonstration of ideal gas law using a cylinder piston system, heating the system so the piston is pushed up, i wanted to calculate the heat transferred into the system, will it be Cp(Tf-Ti) or Cp(Tf-Ti)+ work done by the system ?
48. ### Determine the coefficient of performance of this cycle

Homework Statement In an ideal refrigeration cycle, the temperature of the condensing vapour is 40oC and the temperature during evaporation is -20oC. Determine the coefficient of performance of this cycle for the working fluids; R12 and ammonia. Homework Equations C.O.Pc = TL/(TH-TL) The...
49. ### Calculate Pressure in piston cylinder after heating

Homework Statement Water is contained in a cylinder fitted with a frictionless piston (figure shows that atmospheric pressure acts on piston from above). The mass of the water is 0.45 kg, and the piston area is 0.186 m2. Initially, the water conditions are 110oC and 90% dryness fraction, and...
50. ### Why work done on a system causes heat to flow out of it?

I don't understand how compression of a gas causes heat to flow out of the container of that gas... Could someone please help? Thank you in advance!