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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
23
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
3
3.2 Changes in Matter
Matter can undergo two fundamental kinds of changes. Changes that
do not alter the composition of matter are called physical changes.
Phase changes, in which matter changes from one phase (or state) to
another, are common examples of physical changes. The temperatures at which the phase changes of boiling and melting take place
are important physical properties of substances.
A chemical change occurs when one or more substances
change into new substances. A chemical change is also known as a
chemical reaction. The appearance of new substances is the sign
that a chemical reaction has occurred. In a chemical reaction, the
substances present at the start are called reactants. The new substances that are formed in the reaction are called products. A
chemical reaction is represented by a chemical equation, which
shows the relationship between reactants and products.
Practice Problems
3. Identify each of the following as an example of a chemical
change or a physical change.
a. Moisture in the air forms beads of water on a cold
windowpane.
b. An electric current changes water into hydrogen and oxygen.
c. Yeast cells in bread dough make carbon dioxide and ethanol
from sugar.
d. Olive oil, vinegar, salt, and pepper are shaken together to
make salad dressing.
e. Molten bronze is poured into a mold and solidifies to form a
figurine.
f. A reactant decomposes to form two products.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
23
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
3
3.2 Changes in Matter
Matter can undergo two fundamental kinds of changes. Changes that
do not alter the composition of matter are called physical changes.
Phase changes, in which matter changes from one phase (or state) to
another, are common examples of physical changes. The temperatures at which the phase changes of boiling and melting take place
are important physical properties of substances.
A chemical change occurs when one or more substances
change into new substances. A chemical change is also known as a
chemical reaction. The appearance of new substances is the sign
that a chemical reaction has occurred. In a chemical reaction, the
substances present at the start are called reactants. The new substances that are formed in the reaction are called products. A
chemical reaction is represented by a chemical equation, which
shows the relationship between reactants and products.
Practice Problems
3. Identify each of the following as an example of a chemical
change or a physical change.
a. Moisture in the air forms beads of water on a cold
windowpane.
b. An electric current changes water into hydrogen and oxygen.
c. Yeast cells in bread dough make carbon dioxide and ethanol
from sugar.
d. Olive oil, vinegar, salt, and pepper are shaken together to
make salad dressing.
e. Molten bronze is poured into a mold and solidifies to form a
figurine.
f. A reactant decomposes to form two products.