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Bell work for September
• Carbon atoms can link themselves together into
long chains and rings to form a vast number of
highly complicated molecules. Which of the
following statements BEST explains why carbon
atoms behave this way?
A They easily form ionic bonds with each other.
B They easily form covalent bonds with each other.
C They easily combine with atoms of oxygen.
D They easily become highly charged ions.
Standard 4.8
Summarize evidence (including the evolution of gas;
the formation of a precipitate; and/or changes in
temperature, color, and/or odor) that a chemical
reaction has occurred.
When a chemical reaction occurs, there is
some observable evidence…
• When bubbles form, it may be evidence that a
chemical reaction has occurred and that a
new gas has been formed.
– An example of this is adding an active metal such
as zinc to a hydrochloric acid solution. Hydrogen
gas will evolve. This is evidence that a chemical
reaction has occurred.
• When a precipitate forms, it could be evidence
that an insoluble solid has formed and fallen out
of solution. This is a chemical reaction.
• All chemical reactions there is an energy change.
– When paper burns, heat and light are given off, an
exothermic change. This would be evidence that a
chemical reaction has occurred.
– Many physical changes also involve an energy change.
For instance, melting is an endothermic change.
• Color change can be an evidence for a
chemical change.
• An odor being given off is often evidence that
a chemical reaction has occurred.