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).
39
questions
3
votes
2
answers
116
views
Can we calculate van der Waals' constant a for the following case?
The given Z vs P curve for 1 mole of a gas at 400K starts at Z=1 & P=0.
The slope at the point when the curve again intersect Z=1 is 0.005. The critical temperature of the gas is 500K.
My approach:...
- 163
1
vote
1
answer
76
views
Why is the van der Waals constant b of NH3 less than that of N2?
According to the actual data, van der Waals constant $b$ of $\ce{NH3}$ gas is $\pu{0.0371 L mol-1}$ and that of of $\ce{N2}$ gas is $\pu{0.0387 L mol-1}$.
But it should be,
$$b_{\ce{NH3}}>b_{\ce{...
- 163
0
votes
2
answers
175
views
Why do we subtract the volume correction term in the van der Waals gas equation [duplicate]
The following equation is valid for ideal gasses
$$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 ...
- 19
1
vote
0
answers
62
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.
...
- 127
8
votes
1
answer
474
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 ...
- 111
0
votes
0
answers
111
views
On Van Der Waals relation: how to derive du/dv = a/v^2 without using the relation dU=TdS−PdV?
I have read several threads and papers which show how to derive $\left(\frac{\partial u}{\partial v}\right)_T = \frac{a}{v^2}$
by using the Maxwell's relation $\left(\frac{\partial{S}}{\partial{V}}\...
- 127
0
votes
1
answer
85
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 ...
- 95
0
votes
0
answers
37
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$ ...
- 1
0
votes
1
answer
313
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 ...
- 129
3
votes
0
answers
42
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 ...
- 131
2
votes
1
answer
58
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 ...
- 81
-1
votes
1
answer
90
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 ...
- 11
3
votes
1
answer
479
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 ...
- 59
1
vote
1
answer
74
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$$
when the intermolecular forces are zero $a=0$, so $P=\frac{Nk_BT}{V-Nb}$ which diverges at $V=Nb$ for fixed ...
- 139
0
votes
0
answers
42
views
Should there be a better explanation on Van Der Waals force? [duplicate]
The explanation on how Van der Waals force forms is this: Van der Waals forces consist of induced, temporary dipoles between neighbouring molecules. These are caused by constantly shifting electron ...
- 171
0
votes
0
answers
125
views
Is a/b > 1 mol/L for a and b in the van der Waals equation?
We know that the van der Waals equation for real gases is
$$\left(p + \frac{an^2}{V^2}\right)(V-nb) = nRT.$$
Is $a > b$ always in this equation?
In my textbook $a > b$ for gases like $\ce{He},$ $...
- 225
0
votes
0
answers
75
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" ...
- 1
3
votes
0
answers
69
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 ...
4
votes
2
answers
387
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,...
- 97
0
votes
0
answers
156
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 ...
- 29
3
votes
1
answer
130
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, ...
- 133
0
votes
0
answers
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 ...
- 83
1
vote
1
answer
285
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 ...
- 1,210
1
vote
0
answers
48
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 ...
- 11
3
votes
0
answers
117
views
Does scotch tape only use van der Waals forces? [closed]
Does it also make use of covalent bonds to stick to surfaces?
- 39
0
votes
0
answers
1k
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
1
answer
5k
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? ...
- 203
1
vote
1
answer
191
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 ...
- 358
3
votes
2
answers
693
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 ...
2
votes
0
answers
227
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, ...
- 3,136
0
votes
2
answers
1k
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 ...
9
votes
3
answers
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 "...
- 201
6
votes
1
answer
37k
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 ...
- 825
1
vote
1
answer
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 ...
- 119
1
vote
2
answers
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 ...
- 335
3
votes
2
answers
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$$
I’m very confused about one aspect of this ...
user33789
4
votes
1
answer
5k
views
How are van der Waals parameters determined experimentally?
If the ideal gas law $PV=nRT$ is not enough, as a second approximation the van der Waals equation
$$\left(P+a\frac{n^2}{V}\right)\left(V-nb\right)=nRT$$
is applied. The constants $a$ and $b$ are van ...
- 6,922
9
votes
1
answer
4k
views
Does the van der Waals equation remain valid when repulsive intermolecular forces dominate?
The van der Waals equation for a real gas is:
$$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 ...
- 926
7
votes
3
answers
3k
views
High pressure modification to the van der Waals equation
I get that a gas behaves non-ideally under high pressure and low temperature conditions. At high pressures, the density of a gas increases and attraction forces operate among molecules due to short ...
- 517