What is Van der waals: Definition and 144 Discussions

The Van der Waals radius, rw, of an atom is the radius of an imaginary hard sphere representing the distance of closest approach for another atom.
It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms were not simply points and to demonstrate the physical consequences of their size through the Van der Waals equation of state.

View More On Wikipedia.org
Recent contents Top users
  1. G

    Physical Chem Van der Waals eqn of state

    Homework Statement Use the “virial equation of state”. Measurements for Ar gave B = -21.7 cm3/mol and C = 1200 cm6 /mol-2. Assuming that Ar is a van der Waals-type gas, what are the values of “a” and “b” in the corresponding van der Waals equation of state Homework Equations PV= RT(1+...
  2. Q

    Van der Waals gas - free energy

    For this problem, I'm really jst trying to figure out everything that is going on and then I can simply follow through with the derivatives once I know what I'm working with. Q: For the van der Waals gas, introduce the free energy as F = U – TS and verify that its derivatives over V and T...
  3. L

    What are Van der Waals interactions?

    Homework Statement So basically I'm sort of unclear as to what van der walls interactions are and how they occur...like I know that they're a type of noncovalent bond that occurs between identical groups in two molecules. Like, how do the partial charges appear? (e.g. let's say there are 2...
  4. P

    Van der Waals Graph: What is the Significance of PV & Trough?

    For an assignment, I am graphing using the Van der Waals equation. I am meant to find graph PV (y-axis) over (P). However, I am not sure why. On the internet, most other graphs also use these axes. Why do you use PV though? I am getting a graph that generally similar to those on the internet...
  5. T

    Understanding Van Der Waals Critical Points

    Hi I was studding Van-der-waals equation for real gases when I got in my mind two questions that i couldn't get a sufficient answer for from my professors, hope you have a better explanations : 1- Why there is critical point? It was shocking for me to know that there is a particular...
  6. S

    Van der waals & Andrews curve: discrepancy

    Homework Statement the Pressure (P) versus Volume (V) isotherms of a real gas theoretically obtained form van der waals equation of state approximately overlap with the experimentally obtained isotherms of Andrews for carbon dioxide gas. However, for those isotherms below the critical...
  7. D

    What Are the Dimensions of Constants in the Van der Waals Equation?

    Hi everyone, Struggling with the following question - maths and physics never been my strongest subjects. Thanks in advance 1. An equation of state that has been used to model the behaviour of a fixed amount of a real gas is: (P+a/v2)(v-b)=ZT In the equation Z, a, b are constants, and...
  8. Sirsh

    Van Der Waals Forces: Overview & Q&A

    Hi could someone please give me a run down of these forces? I'm studying them atm but do not really understand them. also, are double and triple bonds representations of 2electrons being shared and 3 electrons being shared? also, when drawing electrondot diagrams for molecules ect. are ionics...
  9. B

    Van Der Waals Forces: Types & Explanation

    Is Van Der Waals forces just a name for all intermolecular forces that exist between molecules or does it only refer to certain types of intermolecular forces?
  10. N

    Solving for volume in Van der Waals Equation?

    Solving for volume in Van der Waals Equation?? Homework Statement Determine the specific volume, v (volume per mass[m^3/kg]) of a water steam at a pressure of 100kPa and a temperature of 500 degrees Celsius by assuming an ideal gas (pV = nRT) and by using the van der Waals equation for n...
  11. P

    Boiling Point & Van der Waals Force: Weight Dependency

    1.Why does boiling point depend on weight ? 2.Does the vanderwall force depend on weight ?
  12. Q

    How Does Van der Waals Equation Approach Ideal Gas Law at Low Particle Counts?

    QUESTION: Van der Waals derived the expression: (P+(a/v^2))(v-b)=RT which is a useful approximation of the equation of state of a real gas. Here a and b are gas dependent constants and v =V/n is the specific volume (Volume V divided by the # of moles of gas molecules) Show that at...
  13. W

    Calculate Isothermal Compressibility of Van der Waals Gas

    Homework Statement Calculate the isothermal compressibility and the expansion coefficient of a van der Waals gas. Show, using Euler's chain relation that \kappaTR = \alpha(Vm - b). Homework Equations van der Waals equation virial expansion of state The Attempt at a Solution So I have to...
  14. W

    Virial expansion of van der Waals equation

    Homework Statement Express the van der Waals equation of state as a virial expansion in powers of 1/Vm and obtain expressions for B and C in terms of the parameters a and b. The expansion you will need is (1-x)-1 = 1 + x + x2 + ... Measurements on argon gave B = -2.17 cm3 mol-1 and C =...
  15. X

    Calculating DeltaH for Van der Waals Gas

    A sample consisting of 1.00 mol of a van der Waals gas is compressed from 20.0 L to 10.0 L at 300 K. In the process, 20.2 kJ of work is done on the gas. Given that u = {(2a/RT)-b}/Cp,m with Cp,m = 38.4 J K-1mol-1, a = 3.60 L2 atm mol-2, and b = 0.44 L mol-1, calculate deltaH for the process...
  16. N

    How Does a Negative First Order Energy Indicate Van der Waals Attraction?

    Homework Statement Hi all Please take a look at this link...
  17. G

    Van Der Waals equation solving for V

    Homework Statement P = RT/(V-b) - a/V^2 Ive been trying to solve this for V and just can't get it. Homework Equations The Attempt at a Solution IVe gotten to: RTV^2 -aV+ab = P(V^3-V^2b) Any Ideas?
  18. T

    Van der Waals equation of state and Maxwell construction

    Hello people :), I have a question because I couldn't understand something written in Schwabl's book of Statistical mechanics. Can you please explain why we in the Van der Waals equation of state choose a constant pressure under the critical temperature. I understood the part that we want to...
  19. G

    Confused About Van der Waals' & Ionic Solids

    Homework Statement Homework Equations The Attempt at a Solution I think Graphite is a Van der Waals' Solid and, er, salt would be an ionic. But I really don't have much of a clue about what the second part is going on about! Thanks! :)
  20. F

    How Do You Calculate the Spring Constant in Van der Waals Potential?

    Homework Statement The van der Waals potential between two inert atoms is often characterized by the expression: http://bama.ua.edu/~stjones/253hw_files/image025.gif Sketch the function. Expand the potential around the minimum in the form U = U(ro) + ½ k(r-ro)2. Evaluate k in terms of s and...
  21. C

    How to express van der waals equation as virial expansion?

    Homework Statement Express the van der Waals equation of state as a virial expansion in powers of 1/Vm and obtain expressions for B and C in terms of the parameters a and b. (Hint. The expansion you will need is (1–x) -1 = 1+x+x2+... . Series expansions are discussed in Appendix 2 of...
  22. S

    Difference between van der Waals forces and dispersion forces

    What is the main difference between van der Waals forces and dispersion forces? This statement confuses me: "van der Waals forces are nearly the same thing as dispersion forces." Right now, I have an idea that van der Waals forces includes these attractions: 1. permanent dipole - permanet...
  23. HappyEngineer

    Van der Waals radius not applicable to most elements?

    I was looking at the values for the Van der Waals radius on various elements in wikipedia and noticed that Molybdenum does not have one. I searched a bit and found this site http://www.webelements.com/periodicity/van_der_waals_radius/ which lists the elements that have a Van der Waals...
  24. N

    How to Derive Van der Waals Equations from Thermodynamic Relations?

    Homework Statement For any Pure Substance, use the relation (1) to show that for a Van der Waals gas, over a range of conditions where c_{v} is effectively constant, that equation (2) gives equations (3) and (4)Homework Equations (1) ~ Tds = du + pdv (2) ~ c_{v}dT + T \frac{\partial...
  25. P

    Van Der Waals Forces: Explaining Role in Molecule Properties

    please explain me importance n role of vanderwaals forces in predicting properties of any molecule
  26. M

    Van der Waals' Forces in Diamond Structures

    very often, most chemistry books claim that the dominant force helding the molecules together to a certain distance apart is van der Waals' forces, which is a kind of intermolecular forces; However, to investigate the forces microscopically, we found that the force is exactly electrostatic...
  27. S

    Are intermolecular and van der waals forces the same?

    are intermolecular an van der waals forces the same thing? I am doing a physics assignment on surface tension and am unsure of what forces are present. i know that there is hydrogen bonding, but what else? thanks
  28. E

    Critical Pressure and Temperature of a van der Waals Gas

    Homework Statement From the van der Waals equation of state, show that the critical temperature and pressure are given by T_{cr} = \frac{8a}{27bR} P_{cr} = \frac{a}{27b^2} Hint: Use the fact that the P versus V curve has an inflection point at the critical point so that the first and second...
  29. G

    Finding Van der Waals Distances for C-C Spatial Interactions

    Hi, I am looking for table or something that gives a tumb of rule for van der Waals distances - I have some C C spatial interactions which I would like to determine if their interaction contributes to the total energy or should I calculate it with a Lennard-Jones potential to get an...
  30. S

    Explaining Adiabatic Process taking Van Der Waals Equations?

    To Forum Physicists / Administrators... Equations for an ideal gas undergoing an adiabatic process are 3 viz 1) P(v^g)=const 2)T(V^(g-1)) =constant and 3)T(P^((1-g)/g))= constant where g=specific heat for const pressure/specific heat for const volume.These equations suits the Ideal gas...
  31. H

    Gibbs Free Energy of Van Der Waals Gas

    Homework Statement Calculate the Gibbs free energy for a van der Waals gas (up to an integration constant), assuming a fixed amount of material and temperature. Homework Equations P = \frac{NkT}{V-Nb} - \frac{aN^2}{V^2} dG = -SdT + VdP + udN (where u is the chemical potential) The...
  32. T

    Solving the Van der Waals Force Problem - Talib

    Hello, Can anyone lead me or give me a hint on how to solve this problem? Interaction between neutral atoms and molecules can be decomposed to two different forces: an attractive force at large distances (the Van der Waals force), and a repulsive force at short distances (due to overlap...
  33. P

    Van der waals parameters a and b

    How, if you're given a pair of molecules, would you decide which one might have a higher value for a or b? As I understand for instance, a's value will be high if two molecules are attracted to each other and b's value will be high if two molecules strongly repel each other... but how would...
  34. J

    Plotting H2O Pressure vs Volume w/ Van Der Waals Gas Equation

    Homework Statement i must use van der waals gas equation to plot a pressure against volume graph for H2O. i must do 3 plots on one graph, one of the critical temperature given a point of inflection, one where temperature is less than the critical temperature giving a large dip in the graph...
  35. J

    Maple Van der Waals Gas Isotherms: Plotting with Maple

    i have to plot isotherms using the van der waals gas theory. i am using Maple to do this but no matter how many different equations i use i cannot get the graphs to look right. it should look like a 1/x curve but with a sharpe trough in it, but all can get is a graph that looks like a normal 1/x...
  36. M

    Van Der Waals Force: A Simple Explanation

    Could You Explain It To Me In A More Simpler Way That I Can Grasp Thanks
  37. E

    Joule-Thomson Expansion of a van der Waals gas

    Hi, Consider a pipe with thermally insulated walls. A thermally insulating porous plug in the pipe provides a constriction to the flow of gas. We model this as a sudden jump in pressure. A continuous stream of gas flows from left to right, with the pressure p_1 upstream being larger than the...
  38. N

    Deriving the Adiabatic Expression for a Van der Waals Gas

    For a van der Waals gas experiencing an adiabatic process derive the following expression: T(V-nb)^(R/Cv) = Constant I tried using PV^gamma = Constant with gamma = Cp/Cv and Cp - Cv = nR with PV = nRT but could not get it. Any hints? I would have to use Boyle's law to account for...
  39. K

    How Does the London van der Waals Force Relate to the Casimir Effect?

    The London van der Waals force is approximatly given by F=-c *a^-7 where a is the distance between two neutral atoms and c is something like this: C=-23*hbar*c/4pi*(alpha1*alpha2) where alpha1 and alpha2 =(epsilon-1)/(4pi*N) and N is the atom number density and epsilon the...
  40. A

    Van der Waals vs. Casimir Force: Explained

    the retarded van der waals force is called the casimir force and the diference between them is that in the oscilations in vacumm between to perfect metallics plates if there is a van der waals force virtual photons reach form one plate to the other in casimir the life time of the photon is not...
  41. A

    Exploring Bonds & Forces in H2O Molecule: Ionic & Van der Waals

    what's the bonding and forces that exist in a water molecule?is it ionic bond and van der waals force?
  42. D

    What Are the Van der Waals Constants for Sulfur Hexafluoride (SF6)?

    Could anyone here say me what's the constants of van der waals for the Sulfur Hexaflouride (SF6)
  43. S

    Exploring Van der Waals Setae Adhesive

    I've been highly interested in the van der Waals setae adhesive since it was discovered how geckos can stick to walls about three years ago. I have a few questions about it though and I haven't found the answers. What does "directional adhesive" mean? Do geckos have to hang from their toes...
  44. enigma

    MATLAB Pressure-Density Relationship with Van der Waals Equation in MATLAB

    I'm having some problems here... Part of an assignment is to find how density of a gas changes as a function of pressure (1 - 700 atmospheres) using Van der Waals. Unless I've really missed the boat, there is no closed form solution for specific volume in that equation, (p+a/v^2)(v-b)=RT...
Back
Top