# 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. ### B Conflicting definition of degree of freedom in Kinetic Theory of Gases

I am seeing conflicting definitions of degree of freedom in my textbook. If I look at the definition given as per screenshot below then it is the number of independent terms/variables/coordinates used to define the energy of a molecule. But, if I look at the statement of Equipartition of energy...
2. ### B Collision time interval of a gas molecule with wall of container

I have been trying to make sense of the derivation of pressure under Kinetic Theory of Gases chapter, but it's not making sense to me when the impulse momentum equation is used for the collision between a gas molecule and the wall of the container. The book says that for the elastic collision...
3. ### A Question about kinetic theory and hydrodynamics (in plasmas)

It is usual, in plasma physics, to combine the kinetic description for electron fluid and the hydrodynamic description for ion fluid, when studying the plasma properties or the dynamics of the electrostatic waves. I am wondering what are the physical meaning and limits of such an approach. Thanks.
4. ### I GHG/GW--QM vs Kinetic Theory

Hi, Folks,...new around here. Please excuse my naivete, but-- I have a problem with the physics behind GHG Theory/GW. Most discussions seem to center around absorbtion/transmission spectra of gases, their correlation with temperature, ala' Black Box radiation and such, and the fact that GHG...

20. ### Kinetic Theory - Mass on a piston

Homework Statement A cylinder containing an ideal gas is in vertical position and has a piston of mass ##M## that is able to move up or down without friction (Fig. 13.2). If the temperature is increases, ...Fig (13.2) (a) both ##p## and ##V## of the gas will change. (b) only ##p## will...
21. ### I What is the significance of calculating the average value of cos?

In kinetic theory, the number of molecules hitting a unit area of a surface per unit time with speeds between v and v + dv and angles between \theta and \theta + d \theta is found to be a function of sin(theta) and cos(theta). There will often be a practice problem asking to show that the...
22. ### A doubt from Kinetic Theory of Gases

I have read Average translation kinetic energy is 1/2RT per degree of freedom and Average translation kinetic energy for an ideal gases is 3/2RT.How? Does it imply f=3 for all ideal gases?
23. ### (2/3) as constant factor In Kinetic theory of gases

Hi I'm in high school but what I'm going to ask you is probably being teached in college. General formula: p=(2/3)*(N/V)*Ek p- pressure N- amount of molecules V- volume of the container Ek - AVERAGE kinetic energy I've been told by my physics teacher, that 2/3 constant factor in kinetic theory...
24. ### Video about pressure in kinetic theory

Hi, I am looking for a video helping intuition on pressure, in the context of kinetic theory of gases. I remember seeing a video where someone poured a bucketful of little hard balls (lead sinkers for fishing?) onto an electronic scales (a dynamometer, really) showing that this corresponds to...
25. ### Elements of plasma kinetic theory, Bittencourt

Homework Statement Consider the motion of charged particles, in one dimension only, in the presence of an electric potential V ( x). Show, by direct substitution, that a function of the form f=f(1/mv^2 + qV) is a solution of the Boltzmann equation under steady-state conditions. Homework...
26. P

### If something moves fast it gains temperature?

Temperature is the average of the kinetic energy of the particles, if the bunch of particle moves fast and you look at the particles in two differece frame of reference, on steady with the bunch of particles and the other not, in the last one you get an higher temperature of the bunch of...
27. ### Activation energy and pre exponential factor

Homework Statement Calculate activation energy and pre exponential factor, i need help with the pre exponential factor Homework Equations Temperature °C -20 = 253 k -10= 263 0=273 10=283 20=293 Rate const. s-1 1.15 3.85 11.3 28.7 74.0 The Attempt at a Solution i already plotted the graph on...
28. ### Classical A source for solved problems in Kinetic theory of gases

I am doing a course on statistical mechanics and we are using the textbook by Mehran Kardar. We are currently dealing with a chapter on kinetic theory. The problem is, I find the exercise problems to be quite tough (and many of my classmates agree with me), and there are no good solved examples...
29. ### Exploring Thermal Effects: What Makes Particles Vibrate?

I've recently begun studying thermal effects. I learned that thermal energy could be transferred within an object through conduction and from a distant object through radiation. (let me know if I'm wrong here) I also learned that when matter is heated, it's particles begin to vibrate, move apart...
30. ### Celsius to Kelvin conversion problem (Kinetic theory)

Homework Statement Find the temperature T that allows the rms speed of a gas to be equal to another gas with T=47°C. The molecular mass of the first gas is 64, and the molecular mass of the second gas is 32. Homework Equations v_{rms}= \sqrt{\frac{3RT}{M}} The Attempt at a Solution The...
31. ### Finding the total translational KE of 1kg of Neon

Homework Statement The screen shot I have attached is the original question, I think I'm ok up until the Ne part. My answer just seems like a ridiculous number, I haven't had much experience with this so don't really know what an 'normal' KE for 1kg of gas would be. Homework EquationsThe...
32. ### Kinetic Theory of Gases- no. of collisions

Homework Statement One mole of oxygen at 27°C and at one atmospheric pressure is enclosed in a vessel. Assuming the molecules to be moving with Vrms, find the number of collisions per second which the molecules make with 1 m2 area of the vessel wall. Homework Equations vrms = √(3RT/M) PV = nRT...
33. ### Kinetic Theory: How many molecules enter pinhole in vacuum?

Homework Statement Pressure in vacuum is 10^-3 Torr. External Pressure is 1atm and 300K. Pinhole of 10^-10cm^2 made in vacuum. Assuming all molecules striking hole pass through, how many molecules leak into vacuum in 1hour? Answer: 10^17 molecules Homework Equations Flux = <v>*N/4V Rate = Flux...
34. ### Assumptions of Kinetic Theory: How big should a cubical element be?

Homework Statement Assuming uniform distribution. What must be the size of a cubical element of volume in the container so that the number of particles in each volume element may vary by 0.1% when the gas is as standard conditions. Probable deviation is given by N^(1/2) where N is the number of...
35. ### Basic Kinetic theory: How many molecules are there?

Homework Statement A closed vessel contains liquid water at equilibrium with its vapor at 100C and 1 atm. 1 gram of water vapor occupies 1670cm^3. Hvap = 2250Jg^-1. How many molecules are there per cm^3 of vapor?How many vapor molecules strike each cm^2 of liquid surface per second? Homework...
36. ### Does the kinetic theory work for solids?

Hello all, i have been asked a question about a lump of iron being warmed, and to calculate the difference between enthalpy and internal energy. I did some algebra and found that the change in the product pV , in the case of a liquid would suffice. But, since the volume doesn't change (Assumed...
37. ### Simple question on kinetic theory of matter

This came up whilst helping my kid with her GCSE physics so ought to be pretty straightforward. Here goes: At his level the kinetic theory of matter is taught in a simple way and one "key point" which is stated time and time again is "the particles in a gas have more energy than the particles...
38. ### Explain convection heat transfer using kinetic theory

I am trying to explain the convection heat transfer and the mass transfer related (buoyancy of the heated part of the gas) using only kinetic theory of gases , I mean using only collisions between molecules of the gas. The environment is the usual one : a hot wall in contact with a gas...
39. ### What temperature actually means?

In ideal gas model, temperature is the measure of average kinetic energy of the gas molecules. If by some means the gas particles are accelerated to a very high speed in one direction, KE certainly increased, can we say the gas becomes hotter? Do we need to distinguish the random vibration KE...
40. ### Kinetic Theory of Gas: F=-2mv/2L/V

F = Δp/Δt http://www.sumoware.com/images/temp/xzhhjttxobbodxgr.png [Broken] (Sorry for bad sketch.. hehe) In the kinetic-molecular theory of gas, the Δp is -2mv (since it's supposed to be elastic collision) But, why the Δt is 2L/V ?? I think it must be a very small time (since the impact is...
41. ### Kinetic Theory of Gases Derivation

Hi, I am struggling with a particular point on the derivation of the kinetic theory of gases. Between 5mins and 6mins 30seconds of the video below they discuss how to get a value for the average of the squared velocities of the molecules in the gas. The bit I don't get is why they divide by 'N'...
42. ### Finding average angle in kinetic theory of gases

Homework Statement "Show that particles hitting a plane boundary have traveled a distance 2λ/3 perpendicular to the plane since their last collision, on average."Homework Equations (Root mean path squared) <x> = 2^(.5)λ λ = ( 2^(.5) * n * sigma )^(-1) ANSWER: The Attempt at a Solution...
43. ### Knudson Effusion between two gasses

Homework Statement Consider two chambers of equal volume separated by an insulating wall and containing an ideal gas, maintained at temperatures T1 = 225K and T2 = 400K. Initially the two chambers are connected by a long tube whose diameter is much larger than the mean free path in either...
44. ### Kinetic Theory of Gas problem

Homework Statement Helium gas with T1 = 500K and P1 = 0.02MPa in a rigid container with volume V = 1 cm^3. Then Helium goes through a process where atoms with kinetic energies greater than kB*T1, where kB is Boltzmann constant, are instantaneously removed from the container. Atoms remaining...
45. ### Escape velocity and kinetic theory

Homework Statement imagine a planet with half the mass and half the radius of Earth ..with temperature reaching 800K k=1.38×10-23 mass of O₂ = 5.3×10-26 does the planet have O₂ or not? Homework Equations ½mv² = ½kT or ½mv² = kT or ½mv²= 3/2 kT either only vertical or anything other than...
46. ### Best Kinetic Theory Book?

Hello everyone, i was looking for suggestions on the beat book in the topic of kinetic theory, i need a book with deep explanation and covers everything from A to Z. I would appreciate it if someone could post a link for their suggestion on amazon or something. thanks in Advance.
47. ### Kinetic Theory Speed distribution (general form)

Homework Statement A molecule has a velocity v and speed v. I've worked out (and understand) that the number of molecules in a gas with speeds between v and v+dv and moving at angles between Ө and Ө+dӨ to any chosen axis is: (1/2)nf(v)dvsin(Ө)dӨ The internet verifies this. f(v) is the speed...
48. ### Newton's First law and KT of Gases

One of the assumptions of Kinetic Theory states that: A gas is a substance composed of many particles flying about randomly, colliding with one another and with the walls of the container. My instructor mention that we might be required to Know, state, and apply this theory to one of newtoms...
49. ### KT of Gases and static equilibrium

In a recent class, my instructor covered the Kinetic Theory of gases. My question is in regard to the theory which states 1) The size of the individual molecues in a gas are so small that their volumes can be considered negligible. The instructor then mentioned that the paticles in the gas can...
50. ### Kinetic theory homework

Homework Statement (Pathria 6.11) Considering the loss of translational energy suffered by the molecules of a gas on reflection from a receding wall, derive, for a quasi-static adiabatic expansion of an ideal nonrelativistic gas, the well-known relation ##PV^{\gamma} = \text{const.}## where...