What is Kinetic theory: Definition and 144 Discussions

The kinetic theory of gases is a simple, historically significant classical model of the thermodynamic behavior of gases, with which many principal concepts of thermodynamics were established. The model describes a gas as a large number of identical submicroscopic particles (atoms or molecules), all of which are in constant, rapid, random motion. Their size is assumed to be much smaller than the average distance between the particles. The particles undergo random elastic collisions between themselves and with the enclosing walls of the container. The basic version of the model describes the ideal gas, and considers no other interactions between the particles.
The kinetic theory of gases explains the macroscopic properties of gases, such as volume, pressure, and temperature, as well as transport properties such as viscosity, thermal conductivity and mass diffusivity. The model also accounts for related phenomena, such as Brownian motion.

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  1. kelvin490

    Question about kinetic theory

    I have a question about deriving the equation of kinetic theory of ideal gas - PV=1/3 Nmcr2, where N is number of atoms, cr is root mean square of atom speed and m is mass of one atom. In deriving the equation, many textbooks consider the total rate of change of momentum within a certain time...
  2. T

    BBKGY equations of kinetic theory

    Are there any good books to understand the BBKGY equations of kinetic theory?
  3. M

    Explaining the 2 in Δt = 2L/vx in Kinetic Theory

    http://en.wikipedia.org/wiki/Kinetic_theory#Pressure_and_kinetic_energy Based on the derivation for P in the above link, one of the early steps was: Δt = 2L/vx which is fine since it is analyzing one specific wall of the container, but then in the next step: F = Δp/Δt = mvx2/L And...
  4. U

    How Does the Kinetic Theory of Gases Describe Particle Collisions?

    Hi guys, I'm studying the Kinetic Theory of gases from Pauli's book Vol. 3. Here he describes a section on the Mean free path, where the probability of two particles with speed v and v' colliding is described as:What is f(v,v') here? Is it the velocity distribution function? If so, isn't it...
  5. D

    How Is Gas Pressure Derived in the Kinetic Theory of Gases?

    Hello! It's been around two months since I started to learn about the knetic theory of ideal gases. But I haven't managed to completely understand it. What I don't understand is how we derive the formula for the presure that the gas molecules exerts on a wall's surface. Here's what I've...
  6. M

    The Kinetic Theory of gases

    Homework Statement The average kinetic energy of a nitrogen molecule at temperature 25c is _____ . Select the correct answer. 1)5*10^(-21) J 2)3*10^(-20) J 3)1*10^(-20) J 4)9*10^(-20) J 5)8*10^(-21) J (i guess they are all wrong ) Homework Equations KE=3/2 K.TThe Attempt at a Solution...
  7. kira506

    Why does the kinetic theory of gases neglect potential energy ?

    My textbook says that the forces of intermolecular attraction between gas molecules are very weak due to large intermolecular spaces between them , that's why they're negligible , Does this have a relation with "force is inversely proportional to the square of distance " (again , I don't know...
  8. xatu

    Kinetic Theory of Gases: Effusion and Collisions

    Question: In the following link I'm concerned with only pages 1 and 2. I'm wondering if there is a typo or an error of some kind. I feel like there is some inconsistency to what the author refers to as \upsilon, \theta, and \phi. The only angle shown in the diagram is \upsilon, which is the...
  9. adjacent

    Kinetic theory and gas molecules

    The kinetic theory states that the gas molecules are randomly colliding with each other and with the wall of the container with high speed.The area of each molecule is very less and as they are moving with high speed,they exert great force. since the pressure is force/area , the pressure should...
  10. Mandelbroth

    Beyond Kinetic Theory of Gases

    Are all collisions between fluid molecules perfectly elastic? I was under the impression that they were not, but now I'm not sure if I'm wrong or not...
  11. M

    Kinetic theory of an ideal monoatomic gas

    Hi everbody! This has been bugging me for quite some time now, so I would be forever grateful and challenge you to think about this. According to the Wikipedia (and phyiscs textbooks), " Since the assumption is that the particles move in random directions, we will have to...
  12. K

    Finding Gas Mass Using Heat Exchange at Constant Pressure and Volume

    Homework Statement The temperature of an ideal gas (M=28kg/mole) has increased 14K by adding 29J of heat at a constant pressure. To cool the gas back to the initaial temperature 20.7J of heat is extracted from the gas at a constant volume. Find the mass of the gas. Homework Equations...
  13. K

    Modelling sound waves in gases with Kinetic Theory

    I am trying to find a description of sound waves and speed of sound in gases using Kinetic Theory. I mean to derive the sound waves in a medium like gas , composed of molecules moving and colliding as Kinetic Theory describes. The origin of the sound wave, as our experience shows, is the...
  14. S

    [Kinetic Theory] Speed of diffusion.

    Homework Statement Find the mean speed of the molecules escaping through a hole of area \sigma. The vessel has volume V and the molecules mass m.Homework Equations dN_w^e = \frac {dA}{4V} w \frac{dN_w}{dw} dw w is the speed. dN_w = \frac {4N}{\sqrt \pi c^3} w^2 \exp {\frac {-w^2}{c^2} }dw...
  15. E

    Explaining Temp Increase When Compressing Gas: Kinetic Theory

    Say you compress a closed container full of gas (you reduce its volume). You are not holding the pressure constant or anything. As you do this, the temperature increases, but why? My best guesses are: - some of the energy you use for pressing down on the container is transferred to heat...
  16. M

    Impulse-momentum theorem and kinetic theory of gases

    Hello, I am reading through my textbook and cannot wrap this idea around my head yet Basically, when a molecule hits the wall of the container, it is reflected back. ΔP = -mv_x -mv_x = -2mv_x = FΔt_collision Then they say the collision occurs every 2d/v_x because that's the time it...
  17. D

    Thermodynamics equation and kinetic theory

    kinetic theory Homework Statement Hi all, I have 1 question that I hope to clarify: Regarding the kinetic theory: it states, that the kinetic energy of ideal gas is 3/2KBT. However, it is stated in my textbook and other sites that kinetic energy of ideal gas is 3/2nRT. The 2 equations...
  18. B

    Explaining Avogadro's Law using kinetic theory

    So far I have found a kinetic-theory explanation of the Boyle's Law, Charle's Law, and Pressure-Temperature Law. For example, for the pressure-temperature law: increasing the temperature of a gas while holding the volume constant causes the gas molecules to collide more frequently with the...
  19. J

    Year 12: Cambridge Physics Problems (2D kinetic theory)

    Question: A square frame of side 10cm rests on a table. Confined within the frame are 500 ants, each of mass 0.001g. The ants rush about randomly with constant speed 0.02m/s, colliding with each other and with the walls. Assuming the collisions are perfectly elastic, calculate for force on each...
  20. S

    Kinetic Theory of Gases: Momentum Change & Force

    The kinetic theory of gas state that p=(1/3)(N)(m)(u^2)/(V). In one step of its derivative related to change of momentum and force given to the wall (Refer to Cubic Container and molecule movement in x,y,z axes in attachment), the equation is given by: change in momentum / time = force...
  21. O

    Kinetic Theory and Elastic Collisions

    Homework Statement When deriving the Ideal Gas Formula from the Kinetic Theory of Gases, we assumed that the gas molecules made perfectly elastic collisions with the walls of the container. This assumption is not necessary as long as the walls are at the same temperature as the gas. Why? The...
  22. D

    Is there a Conceptual problem here? (Pressure in the Kinetic theory of gases)

    I have reviewed recently the demonstration of the formula for the pressure of a gas by using the kinetic theory and it seems that there is a terrible flaw in it, which I will describe below. Can anyone comment on it, please? In all textbooks, the pressure of a gas is proven to be proportional...
  23. L

    What is the relationship between kinetic theory and the gas laws?

    Can someone explain me this theory ? and how to use the equation please I have this in my notes but I don't understand :( Average (translational) Kinetic Energy per molecule is E= 3/2kT The same, per mole, is U = 3/2 * R* T
  24. M

    Kinetic Theory and Activation Energy

    For a reaction to occur, we assume that two particles collide, have sufficient energy to react, and are oriented appropriately...or so I've read. The first one is straight forward. The second two I have questions about. For convenience, let's say A + B-> AB is what we're looking at. This...
  25. F

    Kinetic Theory- Calculating Kinetic Energy

    Homework Statement A quantity of helium gas is held in a square box 1 m length. The measured macroscopic pressure of the gas is 1000 Pa. An atom of helium makes 500 collisions per second with the wall of the container traveling at an average velocity perpendicular to a wall of a container...
  26. P

    Relationship between Electroplating and Kinetic Theory

    Homework Statement I have this assignment from my chemistry teacher and it asks to relate electroplating with the kinetic theory? I don't really understand how the kinetic theory has anything to do with redox, or other chemistry applications. Homework Equations The Attempt at a...
  27. T

    What's a good book for 'Thermodynamics and kinetic theory of gases'?

    The main book we'll be using will be Serway's, but I want a different book that's more focused on the mathematics formulation of thermodynamics and kinetic theory of gases, and not so simple as Serway's. The other 3 books in the discipline's bibliography are: • M.W. Zemansky and R. H...
  28. J

    Kinetic theory and ideal gas

    Homework Statement An ideal gas in a cylinder occupies a volume of 0.065 m3 at room temperature (T = 293 K). The gas is confined by a piston with a weight of 100 N and an area of 0.65 m2. The pressure above the piston is equal to one atmosphere (atm = 1.013x10^5 Pa). The piston is free to move...
  29. G

    Is there a correlation between compressibility factor and temperature in gases?

    Hi I would like to ask is there any relation between compressibility factor of gases and temperature? My textbook says that it always increases with increase in temperature but doesn't explains how? I know that on increases the temperature it is harder for molecules to show attractive...
  30. M

    Kinetic theory of gases - Maximum speed

    If the aleatory speed of a gas rises with pressure and temperature and there is not an apparent limit for these two, what prevents the particles to reach the speed of light? thank you
  31. A

    Kinetic theory: gas/pressure

    Homework Statement An ideal gas is kept in a container of constant volume. The pressure of the gas is also kept constant (a) If the number of molecules in the gas is doubled, does the rms speed increase, decrease, or stay the same? (b) If the initial rms speed is 1300 , what is the final...
  32. B

    Question about gases and kinetic theory

    i have a question that I cannot solve; Show that the rms velocity of a sodium atom moving in a vacuum chamber at 300 kelvin is about 570 metres per second pV=nRT and 3pV=Nm<c^2>
  33. L

    Kinetic Theory of the Ideal Gas

    Homework Statement Find the rms speed in air at 0.0°C and 1.00 atm of (a) the N2 molecules (b) the O2 molecules, and (c) the CO2 molecules. Homework Equations vrms = square root of 3kT/m The Attempt at a Solution (a). 28.0u x (1.66 x 10^-27) = 4.68 x 10^-26 1.5 x (1.38 x 10-23...
  34. R

    Kinetic theory - Maxwell-Boltzmann Distribution

    My (first) question is - is a Maxwell-Boltzmann distribution function a "cumulative distribution function."?
  35. A

    Questions on Kinetic Theory of Gases

    I have some questions on kinetic theory of gases: kinetic theory assumes that the inter molecular force of attraction between two molecules of a gas is negligible. This assumption applies to the condition that the said gas is either at low pressure or at high temperature. This means, when the...
  36. facenian

    What is the Paradox of Momentum Flux in the Kinetic Theory of Gases?

    Hello. There is something I don't understand about the momentum tensor t_{ik}=nm\int f(|v|) v_iv_k of an ideal gas with an isotropic velocities distribution where n is the number of molecules per unit volume and m is the mass of a molecule. Since the the velocity distrubution is isotropic...
  37. B

    Kinetic THeory Question -

    Kinetic THeory Question - URGENT! Homework Statement Ok so we've been asked to show that viscosity n = 1/3 p <v> lambda where lambda is the mean free path, p density of gas and <v> mean speed of particles in a gas I've done this part.. Then the question says that in 1660 boyle did an...
  38. Z

    Solving Kinetic Theory Homework: Work Done By External Agent

    Homework Statement The figure shows the initial state of the gas in an insulated cylinder. The gas is ideal and it is given that, Cp/Cv = 1.5. The insulated piston by the help of an external agent is slowly shifted to the right such that the piston divides the cylinder in the ratio 1 : 3...
  39. Z

    Advanced problem on Kinetic Theory of Gases

    Homework Statement An ideal monoatomic gas is confined in a cylinder by a spring-loaded piston of cross section 8 x 10-3m2. Initially the gas is at 300K and occupies a volume of 2.4 x 10-3 m3 and the spring is in its relaxed state. The gas is heated by a smalll heater until the piston moves out...
  40. Y

    A question about kinetic theory of gases

    Question:Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of gases making up the mixture. Give a convincing argument for this law based on the kinetic theory of gases. Answer to this question from the book I...
  41. S

    Kinetic Theory of Gases Average question

    Hey I'm studying the Kinetic Theory of gases and although it's in a chemistry book it employs physics concepts ergo I have come here to ask you nice people :biggrin: The 5th point is where I have a problem, the rest is just information for you. I am assuming a particle is in a cube (ideal...
  42. O

    Drag calculation based on kinetic theory, flux

    Homework Statement A flat plate is orbiting at an altitude of 250 km around the earth, at an angle of attack &Beta;=45 degrees. Assume that the atmosphere is composed of only atomic oxygen which reflect from the surface diffusely. Calculate the lift and drag if it has an area of 10 M2...
  43. D

    Calculating the Mass of a Gas Molecule Using Kinetic Theory

    Homework Statement A sample of an ideal gas is at a temperature of 320 K. The rms molecular speed at this temperature is measured as 1631 m/s. Calculate the mass of a molecule of this gas Homework Equations rms velocity , u = √(3RT/M ) The Attempt at a Solution Given u = 1631 m...
  44. D

    How Do You Calculate Final Pressure in a Compressed and Cooled Ideal Gas?

    Homework Statement A sample of an ideal gas is both compressed and cooled. The given variables for the gas are: P1 = 90.0 kPa, V1 = 0.0800 m3, V2 = 0.0400 m3, T1 = 300. K, T2 = 260. K. Calculate the final pressure. Homework Equations PV=nRT P1 V1 /T1 = P2V2 / T2 The Attempt...
  45. D

    How Many Oxygen Molecules Are in One Cubic Centimeter at STP?

    Homework Statement At standard temperature and pressure (273 K and 1 atmosphere), oxygen has a mass density () of 1.43 kg/m3. The molecular mass (m) of oxygen is 32 u. Calculate the number (n) of molecules in one cm3 of oxygen. (Round to three significant figures.) Homework Equations...
  46. D

    Temperture And Kinetic Theory

    Homework Statement A brass plug is to be placed in a ring made of iron. At room temperature (20°C), the diameter of the plug is 8.764 cm and that of the inside of the ring is 8.754 cm. They must both be brought to what common temperature in order to fit? Homework Equations Change in...
  47. P

    Statistical Mechanics, Molecular Flux, Kinetic Theory

    Question 1: The mean speed for escaping molecules from a hole is 1.88*(k*T)/m)^1/2 (Eq.1) The mean speed for molecules in the Maxwell-Boltz Distribution is 1.596*((k*T)/m)^1/2 (Eq.2 If you were to calculate molecular flux for an ideal gas, which expression would you use? In my...
  48. M

    Kinetic theory of gases theory question

    Homework Statement Consider a mixture of oxygen and hydrogen kept at room temperature.As compared to a hydrogen molecule an oxygen molecule hits the wall- (a) with greater average speed (b)with smaller average speed (c)with greater average kinetic energy (d)with smaller average kinetic...
  49. H

    Calculating Pressure and Force from He Atoms Colliding with a Wall?

    Homework Statement A square box contain He at 25C. If the atoms collide with wall perpendicularly (90 degrees) at rate of 4.0E22 times/s, calculate pressure and force exerted on wall given area of wall 100cm^2 and speed of atoms =600 m/s Homework Equations PV=Nmv^2 The Attempt at a...
  50. M

    Understanding Kinetic Theory of Gases: Classical vs. Quantum Approaches"

    In the kinetic theory of Gases , we rely purely on classical mechanics. We derive the equations using classical mechanics, and they turn out to be fairly accurate at ideal gas approximation condition of low pressure and high temperature. Now my question is, since in the kinetic theory , we...
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