Read about thermodynamics | 495 Discussions | Page 3

  1. dkeating

    Pressurized gas container gets opened

    Homework Statement I have an empty 2-Liter bottle. It contains 3 g of air inside with an initial air pressure of 1105 mb. When I open it (which is an adiabatic process), I release the pressure which is instantaneous. The pressure then becomes standard atmospheric pressure. What is the...
  2. Jacob Daniel

    Derive an expression from the Gibbs-Thompson relation

    Homework Statement The Gibbs-Thompson relation provides a correlation between solubility and radius of curvature. Consider two spherical particles of radius r and R present in a solvent, with R >> r. The rate of dissolution of the smaller particles (the rate of decrease in its radius with time)...
  3. Jacob Daniel

    Calculate the "surface energy" of succesively smaller cubes

    Homework Statement NaCl has a density of 2.16 g/cm3 and a surface energy of 2x10-5 J/cm2. Calculate the surface energy of 1 g of NaCl. Initially the complete 1 g is in the form of a single cube (of mass 1 g) and progressively broken into smaller cubes with sides of 0.1 cm, 0.01 cm, 10 μm, 1 μm...
  4. N

    I Types of thermodynamic work

    In thermodynamics, what is the relationship between the terms, "pressure–volume work", "mechanical work", "non-mechanical work", "∫pdV", and "-∫Vdp"?
  5. F

    B Machine in Clausius' 2nd law of thermodynamics?

    Hi all, sorry for the condensed title of my post. Any other version of the question I'm trying to ask turned out to be longer than allowed. So, my question is about the wording in some versions of Clausius' statement of the 2nd law of thermodynamics. From time to time I read something like...
  6. A

    I 1st law of thermodynamics with chemical reaction?

    ##dU = dw + dq ## vs ##dU = dw + dq + µdN## Which equation do we apply to a closed system involving chemical reaction? According to textbooks, the first equation holds for any closed system in the absence of fields and kinetic energy. However, later chapters use the second equation for...
  7. F

    B Does a good heat engine make a bad refrigerator?

    Hi all, the efficiency ##\eta## of a generic heat engine working between two temperatures is bound from above by the efficiency ##\eta_{\rm C}## of a Carnot machine working between the same temperatures. That is, if the temperatures are the same, a (ideal) Carnot machine is better than any...
  8. H

    Converting atm to N/m^2

    <Moderator's note: Moved from a technical forum and thus no template.> My homework says: Gas with a volume of 0.004m^3 is heated with a steady pressure of 1,2atm until the volume turns into 0.006m^3. Calculate the work that the gas produces (Given: 1atm=1,013x10^5 N/m^2). I used the Isobaric...
  9. Baibhab Bose

    A Temperature of a thin bulb filament

    In my assignment question, the length L and radius r is given and asked to find out how the Temperature of a thin bulb filament which depends on those two parameters. and the answer is r^(1/4)*L^(-1/2). I cant figure out how. Which relation is involved?
  10. H

    Thermal efficiency of the Rankine cycle

    Homework Statement Calculate thermal efficiency of R-C cycle with saturated steam as shown in the picture. Steam has 4,5MPa when entering into HP part of the turbine (VT in the picture) and expansion on HP is finished at 0,3MPa. Moisture is then removed in the separator and steam is overheated...
  11. P

    How the forces on a drop of water versus mercury on a glass slide influence the shape?

    I am trying to understand how fluids form particular shapes when put on a solid. In the two figures,what are we taking as a system for the forces? How the resultant of the forces influences the shape of the different fluids?
  12. P

    Surface tension in terms of temperature and concentration of an added substance

    Hi! Here's a tricky thermodynamics problem, I hope you can help with it. 1. Homework Statement The boundary between two different materials can be divided into two different kind of phases: bulk phases and surface phases. For example, let's consider a boundary between water and air. We can...
  13. mayank pathak

    I Maximum Work Theorem : Herbert Callen

    Hi, I have been studying thermodynamics from Herbert Callen's "Thermodynamics : an introduction to the physical theories of equilibrium thermostatics and irreversible thermodynamics" In Chapter 4, Section 4.4, he writes : " all processes occurring between a given initial and a given final state...
  14. P

    A Free expansion of a real gas vs Joule-Thomson effect

    I am writing a document on the Joule-Thomson effect. But in my research for it I have come across something that I am not completely clear on. In my document I explained the free expansion of an ideal gas and am trying to transition/segue into the Joule-Thomson effect. However now I am having...
  15. fluidistic

    I Understanding the Seebeck effect

    I'm trying to understand the Seebeck effect in an open circuit of a single material. In other words the system consists of a metal whose ends are kept at different temperature, and we wait long enough for the steady-state to establish. Apparently we can think of the (quasi)electrons in a...
  16. A

    Why is solar radiation equal to long wavelength emission?

    In my heat transfer course, I always had to do analysis of long-wavelength radiation between surfaces first, and find the heat radiated from one of the surface. Then, solar radiation is added to the problem, and suddenly it was said that solar radiation=heat radiated from this surface! Does...
  17. Rain10399

    Finding the pressure of a gas in three identical balloons

    Homework Statement An adiabatic isolated system is formed of three identical balloons (of unknown volume). The balloons are joined by tubes of negligible volume. Each tube has a faucet/tap that is initially closed. The balloons have different quantities of the same ideal gas. After opening...
  18. Dave Mata

    Adiabatic Reversible Compression of a Solid

    Homework Statement Derive an expression for the change of temperature of a solid material that is compressed adiabatically and reversible in terms of physical quantities. (The second part of this problem is: The pressure on a block of iron is increased by 1000 atm adiabatically and...
  19. M

    Isothermal Processes

    I have become almost sure but have only some small doubts. Are all isothermal process actually ideal gas equation PV=mRT? If all such processes are occur in closed systems, this is so. Because it is isothermal the temperature is constant, R is constant and so is mass for a closed system. So the...
  20. D

    I Effect of ambient pressure on newton cooling (water)

    If I have a laboratory water bath (circulated for homogeneity in temp) that I will monitor over a period of time (probably 2 scenarios, an hour at most, and then at least 24 hours or longer), how do I quantify the effect of atmospheric pressure in our test lab. What I will do is use an...
  21. K

    I Reversible compression of a gas - faulty reasoning?

    Hello, I am trying to figure out where my reasoning falls apart in this thought experiment: To determine if a process "A" is reversible (or at the very least internally reversible), I try to picture a reversible process "B" that involves only heat transfer and links the same two endpoints that...
  22. S

    Work done by gas and balloon?

    Homework Statement The question is: One kilogram of a gas with a molecular weight of 35 is contained in a balloon. The initial conditions are 27 C and 0.025 m^3. The gas is slowly heated isothermally until the final volume is 0.05m^3. The atmospheric conditions are 100 kPa and 27 C. The p-v-T...
  23. C

    Heat Capacity relations for 1st order phase transition

    Homework Statement Prove the following relation for which clausius equation holds : Cs=Cp-αV(ΔH/ΔV) Where Cs=∂q/∂T at constant S and is the heat capacity in the coexistence line of 2 phases Homework Equations dq=dU+dW dP/dT=ΔH/(ΔV*T) The Attempt at a Solution I do not fully understand why q...
  24. T

    Confusion about the work done by an ideal gas

    When an ideal gas,in a piston kind of system and whose equilibrium state is mentioned, is allowed to expand (piston is allowed to move and not gas leaking )against a constant external pressure very quickly, then, is the work done by gas zero or not zero ? The arguement for work being zero is...
  25. C

    I The amount of time it will take to melt ice

    What information / formulas do I need to calculate / estimate the amount of time required to melt an ice cube of temperature $T_i$ and mass $m$ in $M$ kg of $T_w$ temperature water? Assume that the system is insulated. Is it even possible? I'm fine with Calculus.
  26. K

    Another Thermodynamics Problem

    1. In vacuum and weightlessness, at the bottom of a cylindrical vessel (a cup), there is a layer of solid substance of molar mass µ. This substance sublimes slowly (evaporates from the solid phase into gaseous phase) and pushes thereby the vessel to the opposite direction. Estimate the terminal...
  27. K

    There is a thermodynamics problem I cannot solve

    1. Consider a balloon which has thick rigid walls and from which all the air has been pumped out. Now, the valve of the balloon is slightly opened, and the balloon is slowly filled with the air from outside. Find the temperature of the air inside the balloon once the air flow has stopped (since...
  28. DaynaClarke

    Finding b in Van der Waals Equation?

    I've got a question that requires me to use the Van der Waals equation in the form: p(V-b)=nRT The process is isobaric, the volume changes from 1m3 to 2m3, and there is 1 mole of the unidentified gas. Ultimately, I need to find initial and final values of T. So I rearranged the formula...
  29. Mentz114

    I Derivation of the partition function

    Starting from the definition of energy levels ##e_n## and occupations ##a_n## and the conditions ##\sum_n a_n = N## (2.2) and ##\sum_n a_n e_n = E## (2.3) where ##N## and ##E## are fixed I'm trying to find the distribution which extremizes the Shannon entropy. Using the frequency ##f_n=a_n/N##...
  30. Bennett Haselton

    I Use internal pressure to compute work done by an expanding gas?

    I would argue that if you are computing the work done by an expanding gas in a frictionless piston, in an irreversible expansion where the inner pressure is greater at all times than the (constant) outer pressure, that you should integrate the internal pressure over volume change, not multiply...