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Chemical Reactions
Only 3 pages.
Which of the following could represent a chemical change?
Atoms are represented by circles, and molecules are represented
by circles that are connected to each other. The different colored
circles represent different kinds of atoms. Note that there are
THREE (3) different kinds of atoms on the LEFT hand side. They are:
White atom , grey atom , and black atom .
The Answer is . Why ?
In ANY chemical change, no atoms are destroyed and no new atoms
are created. Therefore, any of the three kinds atoms (white),
(grey) and
(black) should NOT disappear AFTER the chemical
change. That is, we should have
1.
Since # of WHITE ATOMS on the left is 4, # of WHITE ATOMS on
the right must be 4 also.
2.
Since the # of GREY ATOMS on the left is 4, # of GREY ATOMS
on the right must be 4 also.
3.
Since # of BLACK ATOMS on the left is only ONE, # of BLACK
ATOMS on the right must be ONLY ONE also!
NEXT PAGE, PLEASE!
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4. Only three kinds of ATOMS (white),
(grey), and
(black)
should appear on the right hand side because no new atoms are
allowed to be created from the chemical change (from ANY
chemical change!).
ONLY and satisfy the FOUR conditions described above. But
is NOT a chemical change because NOTHING changes from left
hand side to right hand side. Understand? No? In , NO new
combinations of three different atoms
are formed. The
molecules of right hand side are identical with those of left hand
side. Don’t you think so? That is, no new molecules are formed on
the right (product side). Therefore, in , no new substance is
formed. This is not a chemical CHANGE!
On the other hand, in , new combinations of the three different
atoms (
) appear on the right hand side.
+
+
Compare these combinations with the
combinations on the left hand side of this
chemical change. See the picture on the
preceding page.
Different combinations of 3 different atoms (
(three molecules are formed)
).
So, OINLY “” represents a chemical change.
BUT,
note that the TOTAL number of
particles is CONSERVED in this particular chemical change!
Go to the NEXT page. Please!
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Remember that, in general, the TOTAL number of
“PARTICLES” is NOT conserved in a chemical change. In
chemical changes, BOTH molecules and atoms that are not
constituents of molecules (Like iron atoms) are counted as
PARTICLES.
In “”, the total number of particles before the chemical
change is THREE, and the total number of particles after the
chemical change is THREE also. So, in this particular
chemical change, the TOTAL number of particles is
conserved (remains the Same) before and the after the
chemical change.
Thus, it is NOT always true that the TOTAL number of
PARTICLES is NOT conserved in chemical change! WOW!
Well, is that right?? Seems that the chemical change in “”
may not represent any TRUE ACTUAL chemical change
because NO atoms are specified. I don’t know. I had better
ask some chemistry professor. In my Chapter 6 and Final
Exam, I will take the position for which the TOTAL number of
“PARTICLES” is NOT conserved in chemical changes. OK?
In the chemical change + → , the TOTAL
number of “PARTICLES” is definitely NOT conserved!
On the other hand, in ANY physical change, however,
the TOTAL number of particles is A~~~~LWAYS conserved
only because molecules are NOT broken apart into atoms in
PHYSICAL changes. So, it is impossible to produce any new
combinations of atoms since ALL the atoms still belong to
the same molecules (e.g., water molecules in physical
change melting and boiling).