S4-The Conservation Laws

8/11/2019 S4-The Conservation Laws

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For each problem (momentum, energy &

we will start with an initial chapter dealin

Then, proceed to microscopic level and l

to determine the velocity, temperature an

Then, the equations developed at micros

level are needed in order to provide some

At all three levels of description (mol

microscopic & macroscopic), the conse

Conservation law keeping from chang

We consider two colliding diatomic mole

system.

For simplicity we assume that the molec

The molecules are in a low-density gas,


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In Fig. 0.3-1 we show the collision be

the two homonuclear diatomic molecu

Total mass of the molecules enter

leaving the collision must equal.

Here mA and mB are the masses of m

A and B. Since there are no chemical r

the sum of the momenta of all the at

before the collision must equal that af

in which rA1 is the position vector for

of molecule A, and rA1 is its velocity.


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mass),

with some results of the molecular theo

arn how

concentration profiles in various kinds

copic

input into problem solving at macrosco

cular,

rvation law play a key role.

or to

hold ( a property) constant during

ules

les do not interact chemically and that e

o that we need not consider interaction


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tween

es, A and B, and in Fig. 0.3-2 we sho

ng and

olecules

actions, the masses of the individual

ms

er the collision, so that

atom 1


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ry of the transport phenomena (viscos

f

systems.

ic level.

an interaction

or process.

ch molecule is homonuclear (molecu

with other molecules in' the neighbo


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ty, thermal conductivity & diffusivity)

es composed of only one type of elem

hood.


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ations of the two atoms of one mo

at


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ent).


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ecule by means of position vectors


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drawn from an arbitrary origin.

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S4-The Conservation Laws