Name ______________________________________________Period_____
Understanding Chemical Reactions
(Use with book pages 183-190)
Changes in Matter
1. A _________________________ change does not produce new substances.
2. During a ___________________ change, new substances form.
a. The starting substances and the substances __________________ have
different physical and chemical ___________________________.
b. A chemical reaction is a process in which ____________________ of one
or more substances rearrange for form one or more new ____________.
Signs of a Chemical Reaction
1. Sometimes, changes in ______________________ properties, such as color
or odor, indicate a chemical reaction.
a. Formation of bubbles of a ____________________ can also be a sign of
a chemical reaction.
b. A solid formed when two liquids are mixed is called a _______________
and can be evidence of a chemical reaction.
2. A change in ____________________ is another sign that a chemical
reaction has occurred.
a. _______________________ energy is absorbed or released during a
chemical reaction and is evidenced by warming or cooling.
b. ______________________ energy might also be released during a
chemical reaction.
3. The only way to be certain a chemical reaction has taken place is to
compare the ____________________ of the substances before and after
the change.
What happens in a chemical reaction?
1. During a chemical reaction, _________________________of elements or
compounds ___________________ and form new elements or compounds.
2. Atoms rearrange when chemical ________________between atoms break.
Chemical Equations
1. A ____________________________is a description of a reaction using
element _______________________ and chemical formulas.
2. Element symbols represent ____________________________________.
a. Symbols of elements are shown on the __________________________.
b. When an element exists as a _______________________ molecule, the
element symbol is followed by the subscript 2.
3. Chemical formulas represent __________________________.
a. A chemical formula contains ____________________ symbols and
__________________________ to describe the makeup of a compound.
b. When chemical formulas differ, the represent different _____________.
4. A chemical equation includes the substances that _____________________
and the substances _______________________________.
a. ________________________ are the starting substances in a reaction.
b. _______________________ are the substances produced by a reaction.
c. In a chemical equation, the ____________________ are written to the
left of an arrow, and the ______________________ are written to the
right of the arrow.
d. Two or more reactants are separated by ____________________ signs,
as are any two or more products.
Conservation of Mass
1. The law of _____________________________ states that the total mass of
the reactants before a reaction is the same as the total mass of the
products after the chemical reaction.
2. Mass is conserved in a chemical reaction because ___________________
are conserved.
3. To show that mass is conserved, a chemical equation must show that the
number of each type of __________________________________ must be
________________________, or the same on both sides of the equation.
a. Chemical equations are balanced by adding _______________________.
b. A coefficient is a _________________________ placed in front of an
element symbol or a chemical formula in an equation.
c. In the formula 2H2O, the 2 in front off H2O is a coefficient. This means
there are __________ ____________________ of water in the reaction.
d. Only ____________________________ can be changed when balancing
an equation.
Explain this with the water example
1 – Write the unbalanced equation
2- Count atoms of each element in the
reactants and the products.
3 – Add coefficients to balance atoms