[scientizscht (OP)]

Hello

Let's say we have an amino acid water solution of 1M.

What is the rate that molecules hit a unit of surface in that solution?

Thanks

[chiralSPO]

For a first approximation you will also need to specify the temperature, and whether you mean water molecules and amino acid molecules, or just the amino acid molecules.

Unfortunately this first approximation is probably very poor because a 1M solution of amino acid in water is likely to be quite viscous, which will change the rates at which molecules can move around--and the identity of the amino acid will be important (for instance, glycine and arginine are VERY different!) Also the pH will play a role.

Also, you may wish to consider what the surface is... if the amino acids stick to it very strongly, there may be no reasonable definition of "rate" because the surface will just get covered in molecules that never leave.

As always... the more info you provide about what you are ACTUALLY interested in knowing, the better the answers will be.

[scientizscht (OP)]

Okay, let's say Room temperature and if not aminoacid it could be NaCl or anything really.

I mean the solute's molecules.

The surface is neutral, not sticky or anything.

The concentration can be 1g/L.

[Bored chemist]

Unfortunately this first approximation is probably very poor because a 1M solution of amino acid in water is likely to be quite viscous,

Interestingly, this makes less difference than you would expect.
The viscosity makes it more difficult for the "target" molecules to reach the surface.
But it also makes it less likely that they will drift away.
The two effects nearly cancel.

Similarly, the water gets in the way of the molecules, both coming and going.
So overall, it doesn't have a huge effect.
Which means that you can , to a rough approximation, ignore the water and use the ideal gas laws to calculate it.

https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Collisions_with_container

[JazzHandsMafia]

author=Bored chemist link=topic=77801.msg584055#msg584055 date=1570044342]Which means that you can , to a rough approximation, ignore the water and use the ideal gas laws to calculate it.

newbielink:https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Collisions_with_container [nonactive]

As an unrelated question, the collision theory treatment of the question uses assumes a Maxwell velocity distribution. The fraction of particles with a velocity vector that will hit a unit area of the container surface have a velocity distribution described by the following:



What I'd like to know is if the 'X' between some of the factors represents a cross-product operation or not.

[scientizscht (OP)]

Unfortunately this first approximation is probably very poor because a 1M solution of amino acid in water is likely to be quite viscous,

Interestingly, this makes less difference than you would expect.
The viscosity makes it more difficult for the "target" molecules to reach the surface.
But it also makes it less likely that they will drift away.
The two effects nearly cancel.

Similarly, the water gets in the way of the molecules, both coming and going.
So overall, it doesn't have a huge effect.
Which means that you can , to a rough approximation, ignore the water and use the ideal gas laws to calculate it.

https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Collisions_with_container

Can you provide some sample calculations please or some indicative results?
The equation for impingement rate has many terms without explaining them.

[Bored chemist]

where {\displaystyle \displaystyle k_{B}}\displaystyle k_{B} is the Boltzmann constant and {\displaystyle \displaystyle T}\displaystyle T the absolute temperature defined by the ideal gas law, to obtain


where v is in m/s, T is in kelvins, and m is the mass of one molecule of gas.

where v is in m/s, T is in kelvins, and m is the mass of one molecule of gas.P=...

So all the terms are, in fect, explained.

[scientizscht (OP)]

I need to convert concentration to Pressure using P=concRT.

Is R=kB?

Also what units is the result? Collisions per m3 per sec?

[Bored chemist]

Did you read the wiki page
K_b is the Boltzmann constant.

If you use a consistent set of units the equation will work.
So, the collision rate with a  surface will be in collisions per second per square metre, and so on.

[scientizscht (OP)]

Did you read the wiki page
K_b is the Boltzmann constant.

If you use a consistent set of units the equation will work.
So, the collision rate with a  surface will be in collisions per second per square metre, and so on.

Something is wrong. Assume a solution of 1mM of Lysine in 20C.

The numerator P will be 10^-3 (moles/L) x 8.3x10^3 (R constant) x 293 (temp in K) = 2431
The denominator will be the sq root of 2 x 3.14 x 0.02x10^-23 (mass of a lysine molecule) 1.3x10^-23 (Bolzmann) x 293 (temp in K) = 7x10^-23

This gives a collisions rate of 347x10^23 collisions per sq meter per second.

This means that 58 moles or 8.5kg of lysine will hit a sq meter per second!

This is extremely wrong.

[scientizscht (OP)]

Unfortunately this first approximation is probably very poor because a 1M solution of amino acid in water is likely to be quite viscous,

Interestingly, this makes less difference than you would expect.
The viscosity makes it more difficult for the "target" molecules to reach the surface.
But it also makes it less likely that they will drift away.
The two effects nearly cancel.

Similarly, the water gets in the way of the molecules, both coming and going.
So overall, it doesn't have a huge effect.
Which means that you can , to a rough approximation, ignore the water and use the ideal gas laws to calculate it.

https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Collisions_with_container

How rough is this approximation?
Because I read "For a diluted solution in the gas or the liquid phase, the above equation is not suitable when diffusion takes control of the collision frequency, i.e., The direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with."
https://en.wikipedia.org/wiki/Collision_theory#Collision_in_diluted_solution

[Bored chemist]

Because I read "For a diluted solution in the gas or the liquid phase, the above equation is not suitable when diffusion takes control of the collision frequency, i.e., The direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with."

Do you understand that the rate of collision between a molecule of A and a molecule of B is different from the rate of a collision of A with the wall of the container?

This would all work much better if you actually learned some science.

[Bored chemist]

This is extremely wrong.

Why?

[EnvetteWerMar]

I apologise, but, in my opinion, you are not right. Let's discuss it. Write to me in PM.

[scientizscht (OP)]

Because I read "For a diluted solution in the gas or the liquid phase, the above equation is not suitable when diffusion takes control of the collision frequency, i.e., The direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with."

Do you understand that the rate of collision between a molecule of A and a molecule of B is different from the rate of a collision of A with the wall of the container?

This would all work much better if you actually learned some science.

If a solute molecule collides with solvent molecules before it reaches another solute molecule, the same would apply if it is to collide with the container wall.

[Colin2B]

I apologise, but, in my opinion, you are not right. Let's discuss it. Write to me in PM.

Why are you trying to get people to contact you in pm, what is your motive?? This is not the first time you have made this request.
This forum is for open discussion, if you do not engage in open discussion we will consider limiting your posting rights.

[Bored chemist]

Because I read "For a diluted solution in the gas or the liquid phase, the above equation is not suitable when diffusion takes control of the collision frequency, i.e., The direct collision between the two molecules no longer dominates. For any given molecule A, it has to collide with a lot of solvent molecules, let's say molecule C, before finding the B molecule to react with."

Do you understand that the rate of collision between a molecule of A and a molecule of B is different from the rate of a collision of A with the wall of the container?

This would all work much better if you actually learned some science.

If a solute molecule collides with solvent molecules before it reaches another solute molecule, the same would apply if it is to collide with the container wall.

No, for two reasons.
First- the wall is big.
Secondly, it doesn't make sense to talk about the concentration of a wall, but it does make sense to talk about the concentration of a second material.

[scientizscht (OP)]

But still this equation gives the same number whether the substance is a 150,000g/mole or  150g/mole which is not sensible.

[Bored chemist]

But still this equation gives the same number whether the substance is a 150,000g/mole or  150g/mole which is not sensible.

why is that not sensible?

(Incidentally, I have not bothered to check if you copied the equation correctly.)

[Kryptid]

But still this equation gives the same number whether the substance is a 150,000g/mole or  150g/mole which is not sensible.

Keep in mind that what you are calculating is kilograms per square meter per second, not molecules per square meter per second. Larger molecules will move slower, but they carry more mass.