> Whatever the status of "principles", I think that the statement:
>
> "In a chemical change the atoms in a substance are rearranged
> to make one or more new substances."
>
> is so vague as to be meaningless to a beginning student, and to
> appear wrong to the expert.
>
> For example, some questions that might be asked:
>
>* Is a phase change (rearrangement of atoms in a substance) a
> chemical change ?
>
>* Is there a master "substance" whose atoms can be rearranged to
> make any other arbitrary substance?
>
>* In the second sentence (not quoted) does composition refer to
>"arrangement" ?
>
> [ This reminds me of the quotes from textbooks that Mario Iona
> used to come up with.]
= = = = = = = = = = = = = = = = = = = = = = = =
A student would be confused if the above generalization appeared before
several specific cases. But the author did give examples of physical
and chemical changes before formulating the principle.
1) It is impossible to evaluate the effect of one sentence on students
without examining the context in which it appears.
2) And why "wrong to the expert?" An expert knows that in the context
of examples given to rearrange means to regroup atoms.
> For example, some questions that might be asked:
> * Is a phase change (rearrangement of atoms in
> a substance) a chemical change ?
The author did answer this question before making the generalization.
>* Is there a master "substance" whose atoms can be
> rearranged to make any other arbitrary substance?
What is wrong if such question is asked by a student?
>* In the second sentence (not quoted) does
> composition refer to "arrangement" ?
The second question was: "The result is a change in composition." I
agree that the word "composition" is ambiguous. In this context it
refers to composition of molecules. An expert would know that it does
not refer to macroscopic percentages of different atoms.
> This reminds me of the quotes from textbooks
> that Mario Iona used to come up with.]
Any quote can be ridiculed in some contexts. This reminds me a sentence
I saw today in a serious scientific publication. Referring to new
discoveries the author wrote: "potential errors can be found by clever
critics in any study, no matter how well done."
Lawyers know this. Fortunately, scientists are usually protected from
unscrupulous criticism. What protects them? That is a different
subject. It has to do with moral principles, not with principles that
are laws of nature.
Ludwik Kowalski