Pub #brownchem: @alpha137

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*** Channel started at Wednesday, July 1, 1998 12:42:00 PM

--> A discussion of environmental chemistry
later comentary in blue

alpha137: Started this at around 8:42 am

alpha137: hello

*** Signoff: kewlgirl (Leaving)

*** Signoff: Wuschel (Read error: 131 (Connection reset by peer))

alpha137: who were kewlgirl and Wuschel?

alpha137: hello

*** LizK (gloworm4@171-232-66.ipt.aol.com) has joined channel

#brownchem

LizK: Hello

alpha137: Great, it works

LizK: Finally, I'm sorry about the computer problems I had

alpha137: My first view of enivironmental questions is geological in

nature

alpha137: That is, what were the conditions necessary for the

existance

alpha137: of life on earth?

alpha137: So, my question to you is: What do you think ARE the

necessary conditions for life on earth?

LizK: You mean the organic soup theory type stuff?

alpha137: Well, perhaps just after that, but organic soup is OK.

LizK: Ok, so to sustain life you need basic elements like hydrogyn

and oxygen to produce water

alpha137: yes

alpha137: Geologically speaking, there must have been hydrogen and

oxygen and water.

LizK: but also carbon and silicon and nitrogen and a myriad of

other elements which help to form everything else on earth

alpha137: right.

alpha137: If we had carbon then we had carbon dioxide.

LizK: And in addition to the elements you need heat from the sun

to provide some sort of light and heat, and that helps elements combine

into various compounds

alpha137: Right.

LizK: which react to form all sorts of other things

alpha137: Here is a question: Which is more stable in the presence of

oxygen, carbon, or carbon dioxide?

LizK: carbon dioxide?

alpha137: Yes.

alpha137: Carbon burns to form carbon dioxide.

LizK: because they will combine to fill octet shells etc

alpha137: Yes. The point here is that there is a relative energy scale to chemical elements and
compounds. This is the field of chemical thermodynamics-heat, work, energy and later entropy.
Entropy is a term having to do with order/disorder and the natural tendency in nature to become
more disordered. These things are a part of the First Law of thermodynamics and the Second
Law of thermodynamics. Using these laws we can say powerful things about chemical reactions.

alpha137: Let us back up a bit because my idea here is early earth and

a kind of benchmark for a good environment for life.

alpha137: I am also wanting to get at some fundamental chemical and

physical ideas.

alpha137: There was hydrogen in the atmosphere, but no more. Why? By

the way, there was an atmosphere!

LizK: Ok, but at what point are you starting, is there life yet,

and how much of everything has been formed

alpha137: Perhaps just prior to the organic soup.

alpha137: There is an atmosphere and there is hydrogen in it. Why does

the atmosphere stick around? Why do not the molecules in the atmosphere

just take off into space?

LizK: Does it have to do with the energy it would take to leave is

more than the energy it takes to remain?

alpha137: That is the second part of the question. What keeps things

on earth-you for example. Why do you not just fly off into space?

alpha137: It is physics.

LizK: Gravity!

alpha137: Right!

LizK: Amd wouldn't there be a magnetic pull on body of stuff

floating around that kept it all together

alpha137: Gravity keeps everything here, but there is no hydrogen to

speak of in the atmosphere so why did it leave?

alpha137: Not magnetic! No magnetism is one thing and gravity is another. We are talking
about the attraction between masses and not the magnetic attraction between magnets. The
molecules are non-magnetic excepting in special cases.

LizK: Didn't it combine with other elements too?

alpha137: But why wouldn't the other products leave as well. That is,

if hydrogen combined with oxygen wouldn't the water leave?

alpha137: Put this another way, which molecule could leave the earth

easier, water or hydrogen?

LizK: But what about the gravity principal, water has mass, and

that mass would be pulled to the center of the earth

alpha137: Yes, yes.

LizK: Hydrogen could leave easier

alpha137: Why?

LizK: or more easily rather

LizK: because it is lighter and smaller

LizK: it has less mass

alpha137: Yes, but the force of gravity is an attractive force and if

lighter or heaver the molecules will be attracted to earth! Why would

they leave?

LizK: Did they leave?

LizK: Were they pulled towards other planets, or towards the sun?

alpha137: Well, the hydrogen certainly left.

alpha137: No, the gravitational attraction of the other planets would

be too weak because they are so far away. F = m1 m2/distance

alpha137: Actually, F = g m1 m2/distance

alpha137: Let me ask this, are the molecules in the atmosphere just

sitting there, floating as it were in space above earth?

LizK: Yes,

but they are also combining to make compounds and moving around really

fast and so wouldn't some escape and breakthrough the atmosphere? And

would some of them diffuse out of the atmosphere?

alpha137: OK, really fast is what I am after. Heard of the escape

velocity for rockets?

LizK: Yes vaguely

alpha137: When NASA sends a rocket from earth to a planet the rocket

must escape the pull of the earth's gravity.

alpha137: The usual stuff in the news "escape the pull" is a kind of

distortion since the force goes like 1/distance and there is a "pull"

throughout the universe.

alpha137: There must be a velocity great enough so that the force of

gravity is overcome by the force of leaving the surface of the earth and

ending up at some planet.

LizK: Yes, I knew that, and isn't that why they have to make them

go fast enough - I thought it was that if they were going fast enough

their kenitic energy would be stronger thatn the gravity and other pulls

on the earth?

alpha137: Right, but force of attraction a better way to put it.

LizK: I was talking originally about the first thing you said

about "escaping the pull" of gravity - I diddn't know the velocity stuff

alpha137: Do you think that a heavy rocket would require a greater

FORCE than a lighter rocket?

LizK: Maybe, because the force of attraction would be greater

LizK: Because it would have more mass

alpha137: Well, it turns out that the mass does not matter and so the

escape velocity for a rocket is the same as the escape velocity for a

hydrogen molecule!

alpha137: So why would hydrogen leave the earth's atmosphere?

LizK: Oh, but maybe the hydrogen left but other things don't

because the hydrogen could go faster- Grahms law of diffusion/effusion?

alpha137: That kind of thing.

LizK: I see

alpha137: There is a distribution of molecular velocities and those

molecules having the escape velocity or higher will leave.

alpha137: This distribution is called the Maxwellian velocity

distribution.

alpha137: This is fundamental to chemistry!

LizK: Ok, I understand

alpha137: The Maxwell distribution will depend on the temperature and

the velocities will depend on the KE and hence the mass of the

molecules.

LizK: So that explains why the hydrogen left but the water etc

didn't leave

alpha137: Hydrogen, with its lighter mass, will have more molecules

with the escape velocity and greater than will water.

LizK: Because it can go faster because it is lighter

LizK: So when they are making spaceships, do they make them as

light as they can?

alpha137: In fact, if we plug into the Maxwellian velocity

distribution for water and for hydrogen we will find out that the number

of water molecules with an escape velocity is essentially nil. At a

temperature of 1,000K.
The idea here is that there is a distribution of
velocities and that the distribution is temperature dependent. It has a more or less
rapidly rising form peaking at a certain velocity and then gradually tailing off.I am
speaking of the numbers of molecules vs. their speed for the gas at a given
temperature. We can look at a graph later. That tail, from the escape velocity on
up, represents the numbers of molecules that can escape. In another area, chemical
reactions, some velocity will represent a kinetic energy that is sufficient to
cause a chemical reaction to occur. So this is fundamental to chemistry.
Here is a graph of the Maxwellian velocity distrbution.

LizK: Is that what the temperature was when all of this was

happening/

LizK: oops. I meant?

LizK: not /

alpha137: Spaceships. Yes, but because it will take less energy (to

produce KE) to achieve the escape velocity.

LizK: THat makes sense

alpha137: Well, the temperature of the atmosphere goes something like

this. At the surface it is room temperature (plus or minus) and with

altitude there is a temperature inversion and then an increase. In the

stratosphere the temperature may be high.
This temperature inversion is the same kind of thing that happens closer
to earth-that is, in cities. It can trap air pollutants, but we are getting ahead
of our story.

LizK: So back to the beginning of the earth, the hydrogen that

didn't combine with anything just left the atmospher and that is why

there isn';t much uncombined hydrogen now?

alpha137: These physics things plus the heat and light and the

molecules in the early atmosphere produced a viable, oxygen rich atm

needed for life-soup and all.

alpha137: Yes, to your last stmmt.

alpha137: Is water conserved on earth?

LizK: Yes, I think, doesn't it just change places and phases?

alpha137: Yes. It cannot escape for the reasons we just discussed. So

why are people so worried about water?

LizK: But it can also be broken up into other things like OH- and

H+ and those can be combines with other stuff, so maybe that is why acid

rain is a problem

alpha137: True. And the water in the atmosphere can react with sun

light of low wavelength and dissociate into hydrogen and other stuff and

the hydrogen may leave. Hence a potential loss of water to earth.

alpha137: We need to know, later, how large an effect this is.
It is going to be small!
To make this estimate we need to know how water interacts with sun light. How molecules
absorb light. This is photochemistry. This interaction of molecules with light
is very important in the upper atmosphere. It is also important in the troposphere, near
the surface. Obviously, there is lots of chemistry in the stratosphere and in the troposphere.
Look up the definitions of stratosphere and troposphere in the textbook.

LizK: That is the only tre loss of water though

LizK: when it combines, cant the reactions normally be

neutralized, it may be expensive or not feaseable, but its possible, I

think.
Right, but you are thinking about neutralizing acid rain in rivers and lakes and I am
still thinking about all the water on earth. We can deal with acid rain, etc. later.

LizK: I meant true instead of tre

alpha137: Basically, I think water is conserved. We have another

chemical concept. That of equilibrium.

LizK: Ok, I remember that

alpha137: There must be a "dynamic" equilibrium between water and all

this other stuff like hydrogen ions, etc.

alpha137: Acid rain later, OK.

LizK: So water is constantly breaking itself apart, but it has to

come back together eventually or else it would disrupt the whole

equilibrium

LizK: ?

alpha137: Right.

LizK: But won't it?

LizK: Even if it breaks apart the pH would still be the same if it

were just water

alpha137: Here is another chemical (and physics) concept. That of an

open or a closed system.

LizK: Sure

alpha137: Right to your last stmmt. The pH of water is a constant at a

given temperature.

LizK: But the water on the earth isn't a closed system

alpha137: What makes the earth not a closed system?

alpha137: What is the definition of a closed system?

LizK: Maybe the earth is because not much is coming into it or

leaving it, but the water isn't because there are other elements that

are in the waterect -this is to the first question

LizK: A closed system is one where the reactants and the products

are constant- nothing is being added or taken away from the system

itself, an perhaps the temp. and pressure and vol. are the same too.?

alpha137: Chemists define a closed system as one where no matter

crosses the system boundary. Heat can cross the system boundary however.
Think of a system as a container. In a chem lab the system might be a beaker.
For us, the system is the earth and its atmosphere.Normally, we do not
consider the constituents in the beaker as systems. On the other hand,
if we had two more or less non-missible components we might consider
each as a system and the total as a total system. We could keep track
of each part because they would have a well defined boundary. Get the
idea?

alpha137: The earth is an open system to cosmic rays and stuff like

that, but in terms of the molecules of life it is essentially closed.

Except for light stuff like H2. That is because the H2 leaves what
we have defined as the system-earth and its atmosphere.

LizK: Ok, so the earth would be a closed system, but I don't think

the water on the earth would because matter is crossing the system's

boundary

alpha137: No, no the earth and its atmosphere is the system. Water is

contained within it.

LizK: Ok, but doesn't the water under go reactions?

alpha137: Ignore the very small photochemistry breaking up water into

H2 in the stratosphere.

alpha137: Water undergoes reactions within the earth system, but can

not be lost excepting how?

LizK: I meant like water combining with salt for example

alpha137: Salt is NaCl and water does not combine with it excepting to

dissolve it.

LizK: IT can;t be lost? Unless it is somehow taken out of the

system

alpha137: But water may combine with some other stuff.

LizK: Yes, so doesn't that change the water

alpha137: Yes, water might combine with something and be taken out of

the system in a geological deposit for example.

LizK: But most of those reactions ( when it combines with other

stuff)_ can be reversible if necessary?

alpha137: Yes, and even on a geological time scale, if the stuff were

in geo deposits.

LizK: So water is conserved

alpha137: Yes, My point in this discussion is several fold. First, to

understand our environment we need to look at the geological

perspective, second we have considered some basic chemical principles.

alpha137: We have the idea that the earth is basically a closed

system, that water and

LizK: Ok, so the principle that water is conserved is important

because some people talk as though we were running out of water, but

that isn;t really possible?

alpha137: Exactly.

alpha137: So, what IS the problem with water?

LizK: Well, it combines with so much other stuff which can

contaminate the water so that it isn't safe to use? ANd that it isn't

always very well distributed throughout the earth.
Right, it is basically a problem of distribution. There is lots of water
in the ocean, but it is salty. This salty water is purified by evaporation
and then forming rain. The rain is not evenly distributed around the
earth. So some places have more pure water than others. Then there
is the problem you mentioned of people not treating their water
with the respect it deserves-they pollute it.

alpha137: We have been on for a hour and should stop. Was this useful?

If so what is a good time to do this again?

alpha137: Right, it is a distribution problem.

alpha137: I tried to save our discussion and will review it and

summarize our main points next time.

LizK: Yes this was helpful, I am busy later today so probably

anytime tommorow would be best for me. But what do you want me to do?

Should I read more of the articals on your website or the textbook?

LizK: I've read a number of the articles on the site and I've

started the text book

alpha137: We have our readings to discuss as well. Perhaps you could

also think of the "Tragedy of the Commons" and apply the idea to the

globe itself. Read some of the things having to do with that.

LizK: Ok

LizK: You pick the time

alpha137: In effect we have started with the chemistry of the

atmosphere. The stratosphere that is.

alpha137: Time. How about the same time tomarrow? 9:30 am. Same

network.

LizK: Ok, thats fine

alpha137: See you then. Take care.

LizK: Ok, bye

LizK: thank you very much

*** Signoff: LizK (Read error: 131 (Connection reset by peer))