1. We now have a mixture of 3 substances --- the original compound
QUESTION:
Consider the pictorial representation shown below for a process at the atomic/molecular level. Which process does not involves a chemical change?
Consider the pictorial representation shown below for a process at the atomic/molecular level. Which process does not involves a chemical change?
PAUSE CLICK
A chemical change involves the transformation of one or more substances into other substances.
Let’s examine case A.
We start with a collection of identical molecules. Each molecule is represented in the picture by a pair of circles --- one filled and one unfilled.
HIGHLIGHT
Since the atoms that make up the molecule are not the same, what we have have a sample of a pure compound.
What happens after the change occurred is shown on the right side of the arrow.
We can see that the atoms have rearranged. Two of the molecules have broken up into atoms.
We now have a mixture of 3 substances --- the original compound
HIGHLIGHT molecules on right hand panel
plus two elements…. This one
HIGHLIGHT two unfilled circles on right hand panel
and this one
HIGHLIGHT two filled circles
Therefore, process A involves a chemical change.
CALLOUT “chemical change” pointing to process A
Let’s examine process B.
Here we start with a mixture of a pure compound…
HIGHLIGHT two molecules on left hand panel
And two elements… this one
And this one…
HIGHLIGHT two unfilled circles
And we end up with the same thing….A mixture of the same compound
HIGHLIGHT two molecules on right hand panel
And the same two elements… this one
And this one
Therefore, process B does not involve a chemical change.
The correct answer is B. The question is asking us for the process that does not involve a chemical change.
Let’s verify that process C does involve a chemical change.
We start with a mixture of a compound and an element.
Here’s the compound…
HIGHLIGHT molecules
And here’s the element…
HIGHLIGHT filled circles
And we end up with a mixture of another compound
HIGHLIGHT and two elements….this one
HIGHLIGHT and this one
HIGHLIGHT.
Note that nothing really happened to the element being represented here by filled circles.
The chemical change here involves the break up each triatomic molecule.
Into a diatomic molecule
HIGHLIGHT and an atom
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2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08