What is Gas expansion: Definition and 69 Discussions

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance.

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  1. patric44

    Percentage change in the density of a gas

    Hi all, in this question i was asked to find the percentage change in the density, my approach was as following, first i find the change in volume due to putting the gas into the other vessel as: $$ P_{1}V_{1}=P_{2}V_{2}\;\; → \;\;V_{2}=\frac{P_{1}}{P_{2}}V_{1} $$ now i use $$...
  2. B

    B Loschmidt's paradox and free gas expansion

    Following up on a previous discussion: https://www.physicsforums.com/threads/conservation-of-momentum-in-a-closed-system.1009693/post-6570341 An uncontained system of particles interacting only by elastic collision is the same as a gas undergoing free expansion. If, for simplicity, the...
  3. cianfa72

    I About Reversible vs Irreversible Gas Compression and Expansion Work

    Hi, reading the interesting Reversible vs Irreversible Gas Compression and Expansion Work insight by @Chestermiller I would like to ask for clarification on some points. In the second bullet at the beginning my understanding is as follows: consider an ideal gas contained in a cylinder...
  4. L

    Finding the increase in entropy of the universe in gas expansion

    a) ##P_f=\frac{nRT_f}{V_f}=\frac{nR\frac{T_i}{2}}{2V_0}=\frac{1}{4}\frac{nRT_i}{V_0}=\frac{1}{4}P_i## b) ##Q=\Delta U=nC_V \Delta T=n\frac{5}{2}R(-\frac{T_i}{2})=-\frac{5}{4}nRT_i=-\frac{5}{4}P_i V_0## (##L=0## since the gas expands in a vacuum;Now, (a) and (b) are both correct but not (c), for...
  5. Limebat

    I Does combusted gas travel faster in a vacuum tube?

    Hey all, So if a gas is combusted, would it travel faster through a vacuum tube or a regular ole' tube? I would assume the vacuum tube, as there are less particulates collisions in the way of the fast-moving gas molecules. Yet this also implies pressure on the outside of the thin barrier _ 2...
  6. Limebat

    I What happens when gas is combusted while moving?

    If a combustible gas mixture (say O2 and H2 are combusted to form H2O) are already moving before combustion, what would happen? Intuition tells me the previous velocity (say the gas was moving 150 feet per second) would just add to the velocity achieved when standing still and then combusted...
  7. Z

    Entropy change for spontaneous/ irreversible gas expansion

    When trying to describe why the entropy goes up for a irreversible process, such as gas expanding into a vacuum, it seems fairly easy at a high level. the valve between the two chambers opens, the free expansion occurs, the pressure drops proportional to the volume change and the temp remains...
  8. L

    Thermodynamics: gas expansion formula or approximation error?

    FIRST TYPE: REVERSIBLE PROCESS At the temperature of 127 ° C, 1 L of CO2 is reversibly compressed from the pressure of 380 mmHg to that of 1 atm. Calculate the heat and labor exchanged assuming the gas is ideal. Q = L = - 34.95 J CONDUCT 380 mmHg = 0.5 atm L = P1 * V1 * ln (P1 / P2) = 0.5 * 1...
  9. M

    I How Is Entropy Calculated in an Irreversible Gas Expansion?

    Hi, An irreversible gas expansion is often described in textbooks with a compressed gas in a cylinder pushing up a weight (with mass m) via a hypothetical friction-less and weightless piston. It is said the work done by the gas is equal to -mg × h and from this you can derive the work for a...
  10. Y

    Temperature change in a gas expansion

    1- ##\delta P_V =(\frac{\partial P}{\partial T} )_V \delta T_V## 2-##\delta V =(\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P## so ##C_v \delta T=-P\delta V=-P((\frac{\partial V}{\partial T})_P \delta T+(\frac{\partial V}{\partial P})_T \delta P)## I can...
  11. C

    B Could steam be expanded through a nozzle to get 0°C gas?

    Obviously expanding the gas cools it down. I'm interested if you could boil water and then expand the high pressure steam to cool it down to 0°C. Or are there subtler thermodynamics that would prevent this?
  12. Chestermiller

    Thermodynamics: Gas Expansion with Piston Friction

    A friend of mine and I have been discussing how to apply the first law of thermodynamics to analyze the quasi static expansion of an ideal gas in a cylinder featuring a piston having both mass and friction (with the cylinder). We have identified two different systems that can be used in the...
  13. G

    Volume ratio in an adiabatic gas expansion

    Homework Statement Consider a perfect monoatomic gas at pressure $p_i$ 1.2 atm and temperature $T_i$ 300K, that is in equilibrium inside a cylinder having a volume $V_i=1L$ and which piston has a mass of 1kg and is at an height of 50 cm. Admit that a mass M=3.13kg is over the piston. When that...
  14. M

    I Regarding Joule's gas expansion experiment

    Hi, Joule's original gas expansion experiment is often presented like in the following link: http://demonstrations.wolfram.com/JouleExperimentOnFreeExpansion/ The apparent lack of temperature change in this experiment is often used in textbooks to demonstrate that the energy of an ideal gas is...
  15. T

    Is this Gas Expansion Problem a Quasi-Static Adiabatic Process?

    MODERATOR'S NOTE: Moved from other forum, so no template @Chestermiller I am still having trouble figuring out if a given process is Quasi-static or not. Consider the following case. The cylinder consists of an ideal gas at the bottom and a liquid of density ρ at the top separated by a piston...
  16. C

    I Joule-Thomson Effect: Explaining Qualitatively

    I'm trying to understand the Joule-Thomson effect in a more qualitative way. Here's my attempt at an explanation: Real gases experience intermolecular forces. If we expand a gas whose attractive interactions dominate, it'll cool down. This is due to the potential energy increasing and the...
  17. PHstud

    Liquid to gas expansion temperature change in a tank

    Hello ! I have troube doing a calculation. Let's say we have a volume Vi in a tank at a pressure Pi. If I let my tank open, the tank's liquid will start to boil to keep the pressure Pi inside the tank. Now, at the end, I will have a volume Vf in the tank, and still a pressure Pi. But the...
  18. C

    Calculating Entropy Change for an Ideal Gas Expansion

    MENTOR NOTE: NO TEMPLATE BECAUSE SUMITTED TO WRONG FORUM. 3.1) A quantity of 0.10 mol of an ideal gas A initially at 22.2 degrees C is expanded from 0.200 dm3 to 2.42 dm3 . Calculate the values of work (w), heat (q), internal energy change (delta U), entropy change of the system (deltaSsys)...
  19. Bonapartist

    Thermal energy problem: Gas expansion in cylinder

    Homework Statement A vertical heat-insulated cylinder is divided into two parts by a movable piston of mass m. Initially, the piston is held at rest. The top part is evacuated and the bottom part is filled with 1 mol of monatomic gas at temperature 300 K. After the piston is released and the...
  20. Tardis Traveller

    Ideal Gas Expansion: Finding Depth of Tank

    Homework Statement A bubble comes from the bottom of the tank of water to the surface and triples in its volume. If the temperature of the tank of water doesn't deppend on the depth what is the depth of the tank that the bubble was at? Homework Equations ##PV=nRT## The Attempt at a Solution...
  21. C

    What is the Final Temperature of Methane Gas After Adiabatic Expansion?

    Methane gas at 550K, 5 bar is expanded adiabatically and reversibly to 1 bar. Find the final temperature of the gas. I have made little progress with this... I've calculated the initial volume, and that is all so far. Obviously to find the work usually I'd integrate pressure with respect to...
  22. Cora

    Ideal Gas Expansion State Properties & Exergy Balance

    Homework Statement Two well-insulated rigid tanks of equal volume, tank A and tank B, are connected via a valve. Tank A is initially empty. Tank B has 2 kg of Argon at 350 K and 5000 kPa. The valve is opened and the Argon fills both tanks. State 2 is the final equilibrium state. The temperature...
  23. A

    Thermodynamics (work done by unrestrained gas expansion)

    https://www.physicsforums.com/attachment.php?attachmentid=20388&stc=1&d=1252066499When the partition removed, gas flows into the vacuum until all system has a uniform pressure. Now, is it possible to calculate the work? Let's say gas is not an ideal gas.(Freon 12) We know the volumes of both...
  24. D

    Entropy change of van der Waals gas expansion

    Homework Statement Consider ##n## moles of gas, initially confined within a volume ##V## and held at temperature ##T##. The gas is expanded to a total volume ##\alpha V##, where ##\alpha## is a constant, by a reversible isothermal expansion. Assume that the gas obeys the van der Waals equation...
  25. F

    Ideal Gas Expansion - Finding final pressure and work done by gas

    Homework Statement a ideal monoatomic gas initally has a temperature of 315K and a pressure of 6.87atm . It then expands from a volume of 440cm^3 to volume 1550cm^3 . If the expansion is isothermal, what is (A) the final pressure (in atm's) and (B) the work done by he gas. Homework Equations...
  26. Flutterguy123

    What is the rate of gas expansion in a vacuum?

    Say that there's a large metal box with nothing but a vacuum inside of it, except for a small bag of compressed gas at the center. If the bag were to suddenly pop, is there a specific rate that this gas would accelerate when expanding to meet the space of the container? I think that it might...
  27. P

    Gas Expansion in insulated cylinder (piston & Diaphragm)

    I attached an image of two expansion cases I am analyzing. Both cases involve an insulated cylinder that is divided by a separating element (diaphragm for case A and piston for B). The portion on the right is evacuated. The left contains a calorically perfect gas with an initial pressure and...
  28. W

    Thermodynamics problem for gas expansion at constant-volume

    Homework Statement This is a paraphrase, since this is only part of a 3 part question. A sample of 1.00 mol perfect gas molecules with C_{p,m}=7/2*R and initial pressure of 1.00 atm undegoes constant-volume heating to twice its initial pressure. Find q, w, ΔU, and ΔH.Homework Equations PV=nRT...
  29. T

    Ideal gas expansion between two tanks (Thermodynamics)

    Homework Statement Two interconnected tanks are of equal volume. One is filled with methane at 500bar and 293K, the other is initially evacuated. A valve connecting the two tanks is opened only long enough to allow the pressures to equilibrate. If there is no heat transfer between the gas and...
  30. H

    How do I calculate adiabatic work done by a gas during expansion?

    Homework Statement Hi, I did a lab experiment where I took a 5L vessel made of some material that isolates gas inside and thus behaves like an isolated system (adiabatic). I then pumped gas from ~90kPa to up to 150 kPa... recorded the temperature, then let the gas 'expand' by opening the...
  31. kelvin490

    Problem of gas expansion

    In the case of gaseous expansion, if the pressure of gas is P1 and the external pressure is P2, suppose P2<P1, we know from textbook that the work W is the negative of P2 times the increase in volume, but why P2 instead of P1? We would get different result if we use P1, should the work done on...
  32. C

    Thermodynamics - Ideal gas expansion

    Homework Statement 2.1E5 J of heat enters an ideal gas as it expands at a constant T = 77°C to four times its initial volume. How many moles of gas are there? T=350K, Q=2.1E5 J, Vi=x, Vf=4x Homework Equations ΔU=Q-W W=\intpdV U=nCvT The Attempt at a Solution I'm not sure if I'm even on the...
  33. R

    How can we prove the work done by gas expansion in any deformable container?

    In my textbook W=∫p.dV is only proved for a syringe with a piston. This is quite easily done but the book never explains how it extrapolates to the general situation for a gas expanding in any deformable container. It seems the point is to prove dV= S.h where S is the surface area of a given...
  34. J

    Hot gas expansion rate into outer space

    Good Morning Sirs, it seems to be surprisingly hard to get the numbers of a mystery: How fast expand hot rocket exhaust gases into empty space? Of course aside from its exit velocity! Does the expansion interfere with the impulse direction? I.e. is the impulse omnidirectional effective...
  35. skate_nerd

    C 12B 2009 Problem 17: Finding the Fraction of Air in a Heated Souffle

    Homework Statement Okay so I'm trying to figure out how to get this answer. Theres a souffle made of some ingredients and filled with these ingredients along with some air. Everything starts off at 283.15 K and gets heated in the oven to 463.65 K. Also assume that the air expands with heat...
  36. C

    Work done by gas expansion on piston

    Homework Statement Consider a frictionless piston inside a cylinder, both with a cross sectional area A. 1) By considering the work done by the gas on the piston and the work dW required to move the piston a distance dx, show that the work done by the gas is dW = -pdV. 2) 1 L of an ideal...
  37. U

    Thermodynamic process, gas expansion

    Homework Statement 1kg air with the pressure 10^6 Pa and temperature 398K expands until the volume is 5 times its' initial value. The expansion occurs so that in every moment the absorbed heat energy (dQ) is 1/4 of the work done by the gas. Find the final pressure. 1kmol of air has the mass...
  38. fluidistic

    Adiabatic Gas Expansion: What are the Final Pressure and Internal Energy?

    Homework Statement Two moles of a monoatomic ideal gas expand adiabatically from a temperature T_i=0°C and a pressure of 1 atm until the temperature reaches T=-50°C. 1)What are the initial and final volumes and the final pressure of the system? 2)Calculate the work done by the gas. What are...
  39. V

    Solving a Monatomic Ideal Gas Expansion Problem

    Homework Statement the diagram above of pressure P versus volume V shows the expansion of 2.0 moles of a monatomic ideal gas from state A to state B. As shown in the diagram PA = PB = 600 N/m2 , VA = 3.0 m3 and VB = 9.0 m3. a) i) Calculate the work done by the gas as it expands ii)...
  40. I

    Basic Thermodynamics: Gas expansion against a vacuum

    Homework Statement Okay, so the problem given is that there is a rigid tank with a partition down the middle. For partition A, the specific volume, the temperature, and therefore the pressure is known. The mass, or total volume is not known. Partition B is a vacuum for which the total volume is...
  41. K

    Gas Expansion Question: Calculating Temperature Change for CO2 Release

    1. There is gas tank, contains 5 liters of CO2 under pressure 14.7 MPa, temperatute is 300K. I try to calculate, what temperature gas will have after release (to atmospheric 0.1 MPa and 2000 liters volume). But I cannot :( 2. volume * pressure / temperature = const The Attempt at a Solution To...
  42. M

    Solve Gas Expansion Problem: CO2 Tank, Expansion Chamber & Ambient Heat

    Here is my problem i am working on a project in my free time and am stuck on figuring something out. I am going to be using a CO2 tank which is filled (contains both liquid and gas). I will then open a valve to fill an expansion chamber. This will allow for expansion of the liquid into gas and...
  43. A

    How Does Non-Monatomic Gas Behavior Differ During Expansion?

    Homework Statement A NON-monatomic gas expands from I to F in the Figure (Since it is not monatomic U=3/2nRT does not give you the internal energy, this only works for monatomic gases, instead you must use the first law). The energy added to the gas by heat is 424 J when the gas goes from I to...
  44. B

    Gas Expansion: Exploring Effects of Temperature & Vacuum

    1. why does gas expand to fill a container when there is no increase in temperature or any force applied to it? ( I am confused with the rising effect of gas in air and the expanding effect. how can we distinguis it?) 2. how can we determine the limitation of gas expansion when there is no...
  45. A

    NON-monatomic gas expansion, find internal energy change

    Homework Statement A NON-monatomic gas expands from I to F in the Figure (Since it is not monatomic U=3/2nRT does not give you the internal energy, this only works for monatomic gases, instead you must use the first law). The energy added to the gas by heat is 424 J when the gas goes from I to...
  46. 2

    Thermodynamics Problem gas expansion

    We have been given this problem through university and I am stumped! Consider a propane tank that initially contains 5 L of liquid propane at the environment temperature of 20 degrees C. If a hole develops in the connecting tube of the propane tank and the propane starts to leak out...
  47. W

    Gas expansion at constant pressure

    Homework Statement 2 moles of gas at 300 K at 0.02 m3 is expanded to twice the original volume at constant pressure, and then adiabatically until T = 300 K again. assume monatomic gas. assume ideal. determine the final volume determine the heat supplied to the overall process determine...
  48. J

    How Does a Monatomic Ideal Gas Behave When Heated and Compressed in a Cycle?

    Suppose 1.2 mol of a monatomic ideal gas initially at 11 L and 300 K is heated at constant volume to 590 K, allowed to expand isothermally to its initial pressure, and finally compressed at constant pressure to its original volume, pressure, and temperature. During the cycle, what are (a) the...
  49. I

    Calculating Work Done by a Gas Expansion

    Homework Statement A gas is initially at (20 Pa, 3 m3) and expands to (30 Pa, 17 m3). The minimum amount of pressure the gas can be under is 9 Pa, and the maximum pressure the gas can be under is 40 Pa. Find the minimum amount of work that can be done by the gas in going from its initial...
  50. F

    Question of Work with non-ideal gas expansion

    Homework Statement Consider a system described by the van der Waals equation of state which expands at constant temperature from volume V1 to volume V2. Assume that the density g= N/V ≪ 1 over the range of volumes of interest. (a) Calculate the work Wvdw done on the gas to the lowest...
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