# Questions tagged [van-der-waals-behavior]

Questions with substantial discussion on the behavior of real gases using the van der Waals model (as opposed to just calculations with the van der Waals equation, or a casual reference to the van der Waals model).

40 questions
Filter by
Sorted by
Tagged with
1 vote
116 views

### How does a dry shampoo work?

From my chemistry knowledge, I know that soaps are made from fatty acids and some sort of base and this reaction also gives us $\ce{H_2O}$ so the grease in hair dissolves and gets washed away in water....
57 views

### How could I desorb the CO2 molecules contained in the pores of activated carbon?

I have CO2 trapped in my activated carbon. What would be the most environmentally sustainable way to release it? I have heard of PSA (Pressure Swing Adsorption), which works when the adsorbent is ...
1 vote
105 views

524 views

### Why do we subtract the volume correction term in the van der Waals gas equation [duplicate]

The following equation is valid for ideal gasses $$pV=nRT$$ Please mind the following notation, any parameter that is related to an ideal gas would be denoted with a subscript $i$ and anything related ...
1 vote
111 views

### What’s the physical meaning of (∂v/∂T )P?

I'm solving this exersice: The equation of state of a Van der Waals gas is \begin{equation} \left(P + \frac{a}{v^2}\right)(v-b) = RT \tag{1} \end{equation} Where $a$,$b$ and $R$ are constants. ...
617 views

### Confusion in Van der Waals Equation

I understand that the behavior of ideal gases deviates largely from that of real gases in terms of pressure exerted by the gas molecules on the container in which it is present, space available for ...
1 vote
246 views

### Why is the excluded volume in van der Waals 4 times the actual volume of the gas molecule?

I am having trouble understanding why the excluded volume of a particle is four times its actual volume. According to Wikipedia, "The excluded volume b is not just equal to the volume occupied by ...
61 views

### How should I evaluate $\left(\frac{\partial U}{\partial V}\right)_T$ with van der waals equation: $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$?

So in my homework I was able to get this- $\left(\frac{\partial U}{\partial V}\right)_T = T(\frac{\partial P}{\partial T})_V - P$ but now I'm trying to plug in $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$ ...
517 views

### Cubic nature of van der Waals' gas equation

$V_m^3-\dfrac{RT+bP}{P}V_m^2+\dfrac{a}{P}V_m-\dfrac{ab}{P}=0$ So, At $T<T_c$ the above equation has three real roots say $V_1,V_2,V_3$, my doubt is what does this mean physically because for some ...
43 views

### Experimental Verification of Van der Waals parameters?

I am currently trying to find an academic paper that experimentally verifies the a and b values of Van der Waals forces for carbon dioxide. I can't seem to find this, and am wondering if I am missing ...
109 views

### Best description of forces/ mechanisms that stabilize the interaction between a hydrophobic protein binding pocket and a hydrophobic ligand

This is a more theoretical or definition question that is related to the terms "hydrophobic effect", "hydrophilic interaction", and "van der Waals' forces" (and others I ...
120 views

### Why do we use the ratio of Critical Pressure and Critical Temperature to calculate size of a gas molecule?

Our teacher explained that using the ratio of Critical Pressure and Critical Temperature is preferred over Critical Volume to calculate the size of a gas molecule when all these quantities are taken ...
571 views

### If a = 0 for a Van der Waals gas, what does that signify?

I know that if $a = 0$ for a gas at certain temperature and pressure, it means that the molecules of gas have almost no attractive forces acting between them. But does that also mean that the ...
1 vote
108 views

### What happens when $V=Nb$ in the Van der Waals equation (divergent)?

The VdW equation: $$\left(P+a\left(\frac{N^2}{V^2}\right) \right)\left(V-Nb\right)=Nk_BT$$ when the intermolecular forces are zero $a=0$, so $P=\frac{Nk_BT}{V-Nb}$ which diverges at $V=Nb$ for fixed ...
43 views

### Should there be a better explanation on Van Der Waals force? [duplicate]

The explanation on how Van der Waals force forms is this: Van der Waals forces consist of induced, temporary dipoles between neighbouring molecules. These are caused by constantly shifting electron ...
91 views

### Are spontaneous/induced dipoles the same as van der Waals forces?

I am puzzled by the names of dipoles. What is the difference among permanent dipoles, spontaneous dipoles, van der Waals forces, and intermolecular forces? Does "The intermolecular force" ...
94 views

### About Real Gas and Ideal Gas - Select the correct statement(s):

Select the correct statement(s): At Boyle's temperature a real gas behaves like an ideal gas at low pressure. Above critical conditions, a real gas behaves like an ideal gas. At high pressure van der ...
835 views

### Why London Dispersion force is attractive not repulsive

The London Dispersion force is caused by the formation of temporary dipoles in the electron cloud of neutral atoms that attract each other. Why is this only attractive? Why don't the like poles repel,...
208 views

### When do repulsive forces in a gas actually become dominant?

We say that repulsive forces become dominant when Z>1 (i.e. Vobserved > Vtheoretical). But when the difference between Vobserved and Vtheoretical is less than b, shouldn't attractive forces ...
139 views

### Intermolecular interaction Van Der Waals

In the empirical demonstration of the Van der Waals equation at Khan Academy, they made a demonstration of the real volume, for example, it was said that it has to be larger than the ideal volume, ...
52 views

### Why is the concentration term in van der Waals correction for ideal gas squared? [duplicate]

In van der Waals correction for ideal gas equation, the pressure term has a correction where concentration term is squared. I saw derivations for this and they say that the concentration is squared ...
1 vote
421 views

### interconverting Van Der Waal's equation for real gases from number of molecules to density

I want to ask a question about Van Der Waal's equation for real gases. I was shown the following formula for real gases (VDW) which accounts for the liquification of water vapour which is not possible ...
1 vote
76 views

### Student Question regarding molecular van der Waals volume and Polarizability

I would like to request a crosscheck of my understandings regarding molecular van der Waals volume and polarizability. Please have a look through my statements about these 2 concepts below and point ...
147 views

### Does scotch tape only use van der Waals forces? [closed]

Does it also make use of covalent bonds to stick to surfaces?
2k views

### What is the value of isothermal compressibility of a van der Waals gas at critical point?

For a van der Waals gas, isothermal compressibility is $$\kappa=\frac{V^2(V-nb)^2}{nRTV^3-2an^2(V-nb)^2}$$ If one substitutes the values of critical temperature and volume in this formula, isothermal ...
1 vote
6k views

### Chemicals to increase surface tension of water

I want to increase the surface tension of water by 1.2 - 2 times. How about adding one or more chemical substances to the water that can possibily increase its surface tension by the desired amount? ...
1 vote
300 views

### Deviation from ideal gas law curves

So I was reading through my textbook on deviations from an ideal gas, and they had plotted a curve of experimental PV/nRT against the pressure. They talk a lot about why the volume is really smaller ...
754 views

### Compressibility factor (Z) of a real gas [closed]

I was wondering whether the compressibility factor of a real gas (given by $Z = V_{\mathrm{real}}/V_{\mathrm{ideal}}$) is supposed to be measured while keeping pressure constant? I was attempting to ...
276 views

### Why is it experimentally difficult to accurately find the critical volume of a real gas?

I was reading up on the derivation of the values of various critical state functions( $\ce{Vc}$, $\ce{pc}$ and $\ce{Tc}$) from the Van der Waals equation (Physical Chemistry by G.W. Castellan). There, ...
2k views

### Finding (∂U/∂V )T = n^2a/V^2 for a van der Waals gas [closed]

$\displaystyle dU = \left(\frac{\partial U}{\partial T}\right)_V dT + \left(\frac{\partial U}{\partial V}\right)_T dV \to dU = C_v dT - C_v\left(\frac{\partial T}{\partial V}\right)_U dV$ Not sure ...
3k views

### How are the Van der Waals constants a and b related to each other?

I know that the constant $a$ represents the attractive forces between the molecules while the constant $b$ represents the size/repulsion between them. Does that mean that $a$ and $b$ are "...
39k views

### Calculating Compressibility factor from the Van der Waals' Gas equation

So this problem has been bugging me for a long time. According to Wikipedia the compressibility factor $Z$ is defined as the ratio of the volume occupied by a real gas divided by the volume occupied ...
1 vote
2k views

### Validity of van der Waals equation [duplicate]

Van der Waals had stated that at high pressure, pressure exerted by ideal gas on the walls of container is more than real gas. However in this graph, one can clearly see that, the at high pressure ...
1 vote
5k views

### Are van der Waals coefficients independent of temperature?

In the van der Waals equation for real gases, the coefficients $a$ and $b$ are used as respective correction terms for pressure and volume in the ideal gas equation. I want to know whether the van ...
5k views

### Van der Waals real gas equation

Van der Waals corrected the ideal gas equation for real gases and gave the following equation: $$\left(p+\frac{an²}{V^2}\right)\left(V-nb\right)=nRT$$ I’m very confused about one aspect of this ... 5k views

### How are van der Waals parameters determined experimentally?

If the ideal gas law $PV=nRT$ is not enough, as a second approximation the van der Waals equation $$\left(P+a\frac{n^2}{V}\right)\left(V-nb\right)=nRT$$ is applied. The constants $a$ and $b$ are van ...
The van der Waals equation for a real gas is: $$RT =\left(p+\frac{a}{V_\mathrm{m}^2}\right)(V_\mathrm{m}-b)$$ We have understood this formula by saying that $a$ is the term which is for force of ...