Chemical Reactions - Broadneck High School

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Chemical Reactions
Remember the Krebs Cycle?

The Citric Acid Cycle is also known as the
Krebs Cycle or Tricarboxylic Acid (TCA)
Cycle. It is a series of chemical reactions
that takes place in the cell that breaks down
food molecules into carbon dioxide, water,
and energy.
Chemical Reactions
We know that electrons make bonds.
 We know that bonds make chemicals.
 What do chemicals do?

What do you already know
about chemical reactions?
With your neighbors list at least 3 things you
already know about chemical reactions.
 They create chemical changes.
 New, different chemicals are formed.
 They break/form chemical bonds.
 Atoms can’t be created or destroyed.
Chemical Reaction:
the process by which one or more
substances are changed into one or more
different substances.
 Chemical reactions create new chemicals.
 They do this by breaking/re-forming
chemical bonds.
What happens when Hydrogen (H2) and
oxygen (O2) come together to create water
(H2O)?
•
•
•
I have the same number of each atoms on each side.
Green bonds are bonds that get broken. Red bonds are
bonds that are re-formed.
I have different chemicals on both sides of the reaction.
Signs of a Chemical Reaction
Signs of a Chemical Reaction
1. Color changes - Different combinations of
molecules reflect light differently. A color
change indicates a change in molecules.
2. Heat content changes - In all chemical
reactions, the heat content of the reactants
and the content of the products is never the
same. Sometimes the difference is great
and can be easily detected; at other times
the difference is slight and is more difficult
to detect.
Signs of a Chemical Reaction
3. A gas is produced - Whenever a gaseous
product forms in a liquid solution, bubbles
can be seen. A colorless gas produced in a
reaction of solids is much harder to detect.
4. A precipitate forms - Precipitates are
insoluble products formed by a reaction
taking place in a liquid solution. This
insoluble product will eventually settle to
the bottom, but might immediately appear
by turning the clear solution cloudy.
Homework
HW: Read Physical Changes on pg# 42 &
Chemical Changes pg# 53-55
 Do 2.4 Section Assessment pg# 55
Answer question #28-34.
Write out the question and answer for credit.

Solutions
28.
29.
30.
The composition of matter always changes
during a chemical change.
a transfer of energy, change in color, the
production of a gas, the formation of a
precipitate
The mass of the products is always equal
to the mass of the reactants.
Solutions
31.
32.
33.
34.
In a physical change, the chemical
composition of a substance does not
change. In a chemical change, the
chemical composition of the reactants
changes as one or more products form.
a. physical
b. physical
c. chemical
d. chemical
Mass is conserved in every physical
change or chemical reaction.
43.2 g

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