Question

reflect
when you combine two or more substances called reactants, the atoms
interact, rearrange, and produce new substances called products. a
chemical reaction takes place. some chemical reactions take place
quickly, such as a burning match. others require more time, such as
chains left outside for a month exposed to weather, which causes the
iron to react with the oxygen in the air, producing a new compound
called iron hydroxide, or rust. this overall reaction can be described in
writing with the following chemical reaction equation:

$$ 4 mathrm { fe } + 6 mathrm { h } _ { 2 } mathrm { o } + 3 mathrm { o } _ { 2 } ightarrow 4 mathrm { fe } ( mathrm { oh } ) _ { 3 } $$

chemical reaction - a process by which
two or more chemical substances
interact and are chemically changed,
producing different chemical substances
what do you think?
take a look at the pictures below of a smelly, rotting pumpkin; a burning campfire; and some
tarnished silverware. these images are examples of chemical reactions taking place. in each
image, how do you know a chemical reaction is taking place?
we can observe evidence of chemical reactions.
scientists confirm that a chemical reaction has occurred by determining if a new substance with
new properties was formed, sometimes using instrumentation. in most chemical reactions, there
are signs that indicate a chemical reaction has occurred. if you observe one or more of the signs,
this provides evidence that a chemical reaction may have taken place. five possible signs of a
chemical reaction are production of a gas, production of light, unexpected temperature change,
unexpected color change, and the formation of a precipitate. these signs can be helpful as long
as we remember that the only way to be certain that a chemical reaction has occurred is to identify
a new substance that was produced in the reaction. remember, not all chemical reactions will
produce one of the five signs.
evidence of chemical
reactions

Explanation:

• Rotting pumpkin: A new substance is formed as the pumpkin decomposes, and there may be a change in color and an unpleasant smell (which can be related to the production of new chemical substances).
• Burning campfire: There is a production of light (and heat), which are signs of a chemical reaction. Also, new substances like ash and gases (such as carbon dioxide) are formed.
• Tarnished silverware: A new substance (silver sulfide, which causes the tarnish) is formed, indicating a chemical reaction.

Answer:

• For the rotting pumpkin: A new substance is formed (decomposition products), and there may be color change and smell (related to new chemical substances).
• For the burning campfire: Production of light (and heat) and formation of new substances (ash, gases like \(CO_2\)).
• For the tarnished silverware: Formation of a new substance (silver sulfide).