Chemical Reactions

Chemical
Reactions

UNIT 2: Atoms and Interactions of Matter

Chemical Reactions

A chemical reaction is the
process in which atoms
are rearranged to produce
new substances.

Chemical Reactions

During chemical reactions,
bonds between elements and
compounds are broken and
new bonds are formed as
new substances are
produced.

Multiple Choice

What happens during a chemical reaction?

• atoms undergo a physical change

• atoms gain mass

• atoms lose mass

• atoms are rearranged to form new substances

Chemical Reactions

A chemical formula uses
chemical symbols and
numbers to represent a
given substance.

Chemical Reactions

The following is a chemical
formula:

NaCl

Multiple Choice

Which of the following is a chemical formula?

• NaCl

• 6CO2 + 6H2O → C6H12O6 + 6O2

• 2H2 + O2 → 2H2O

• C + O2 → CO2

A chemical equation is an
expression that uses symbols
to show the relationship
between the starting
substances and the substances
that are produced by a
chemical reaction.

Chemical Reactions

The following is a chemical
equation:

6CO2 + 6H2O → C6H12O6 + 6H2O

Multiple Choice

Which of these is a chemical equation?

• HCl

• NaH3

• 2H2 + O2 → 2H2O

• CH4

Chemical Reactions

Reactants are the
substances that participate
in a chemical reaction.

Chemical Reactions

Products are the
substances formed in a
reaction.

Multiple Choice

In the following equation, 2Na + Cl₂ → 2NaCl, the product is 2Na + Cl. True or False?

• True

• False

Chemical Reactions
The arrow sign in a
chemical equation is
known as the yields sign
and points from reactants
to products.

Chemical Reactions

Law of conservation of
mass states that matter is
neither created nor
destroyed.

Chemical Reactions

This means that a
chemical equation must
show the same numbers
and kinds of atoms on
both sides of the arrow.

Multiple Choice

Which law applies to the need for chemical equations to be balanced?

• The law of conservation of mass

• The law of conservation of energy

Chemical Reactions

Endothermic reaction is a
chemical reaction that
requires an input of
energy.

Chemical Reactions

Exothermic reaction is a
chemical reaction in which
energy is released to the
surroundings.

Multiple Choice

Which of these reactions absorbs energy?

• endothermic reaction

• exothermic reaction

The law of conservation of
energy states that energy
cannot be created or destroyed.
The total amount of energy does
not change during endothermic
or exothermic reactions.

The rates of chemical reactions
can be affected by the
concentration of reactants, by
the surface area of reactant
particles, by higher
temperatures, and by catalysts.

Chemical Reactions SUMMARY

▪Bonds are broken and
formed during chemical
reactions to produce new
substances

Chemical Reactions SUMMARY

▪A chemical equation uses
symbols to show the
relationship between the
products and the
reactants.

Chemical Reactions SUMMARY

▪The law of conservation of
mass requires that
chemical equations be
balanced.

Chemical Reactions SUMMARY

▪Exothermic reactions
release energy to the
surroundings, and
endothermic reactions
absorb energy from the
surroundings.

Chemical Reactions SUMMARY

▪Reaction rate is affected
by reactant concentration,
temperature, surface area,
and catalysts.