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Re: What are "principles" in science?



REPOSTING A LOST (?) MESSAGE.

I should have stated that the author did explain
(in the introductory chapter from which I quoted)
a difference between compounds and mixtures.
The example used was mixing powdered S and
Fe at room temperature (and unmixing them
with a magnet). Doing the same at an elevated
temperature creates a new substance, FeS.
Chemical change was defined as making a
new substance; the phrase "chemical reaction"
does not appear in the introductory chapter.

Thanks for answering my question, JohnD
and JohnC. Examples of laws which are not
equations (principle of conservation of energy
and Newton's first principle) were very
appropriate in this context.

Ludwik Kowalski wrote:
After elaborating on what (a) experimental facts,
(b) hypotheses, c) theories and (d) laws are in
science an author of a textbook inserted:

"A PRINCIPLE TO REMEMBER. In a chemical
change the atoms in substances are rearranged
to make one or more new substances. The result
is a change in composition."

Would it be appropriate to replace the word
PRINCIPLE by the word LAW?

There are several questions on the table.

1) We can agree that the alleged principle needs repair.

2) Replacing principle --> law is permissible, but doesn't
solve the main problems.

Scientists use a number of words such as law, principle,
rule, etc. almost interchangeably. Of course there are
connotations and nuances, but they are rarely if ever
important.

3) The alleged principle is so messed up that one hardly
knows where to begin criticizing it.
*) Do the two sentences express two principles or just one?
*) Is it trying to define the notion of "chemical change"?
-- If that is the same as a chemical reaction, why
introduce nonstandard terminology?
-- If that is not the same, the distinction needs to be
clearly explained.
*) For example, what about an allotropic change such as
tin pest? There is a rearrangement of atoms, but no
real change in composition.
*) For a different example, suppose I mix oil and lemon
juice and egg-yolk to make mayonnaise. There is
rearrangement of atoms and a change in composition,
but does it really count as a _chemical_ change?

One should also keep in mind the law/rule/principle of
pedagogy that learning proceeds from the known to the
unknown. The alleged principle doesn't do much good
unless the students already have a decent understanding
of "substance" and "composition" et cetera.