Chemistry
Intro to Chapter 9 – Chemical Reactions
Name _______________________________
Period ______
1. Writing molecular formulas – (You all know this, but it’s good to review and think about
how to do this.) Write the formula for the following molecules. Use SUBSCRIPTS to show how
many atoms of an element are in the molecule. Place the subscript AFTER the element symbol. Do
NOT use a subscript of one (1). THESE MUST BE WRITTEN PERFECTLY – ELEMENT
SYMBOLS CORRECT AND NUMBERS ARE SUBSCRIPTS.
Example: Magnesium bromide (1 atom magnesium, 2 atoms bromine)
a. Calcium chloride (1 atom calcium, 2 atoms chlorine)
MgBr2
_____________________________
b. Aluminum chloride (1 atom aluminum, 3 atoms chlorine) _____________________________
c. Ozone (3 atoms oxygen)
___________________________
d. Dichloromethane (1 atom carbon, 2 atoms hydrogen, 2 atoms chlorine) ____________________
e. Aluminum oxide (2 atoms aluminum, 3 atoms oxygen)
______________________________
f. Glucose (6 atoms carbon, 12 atoms hydrogen, 6 atoms oxygen) ___________________________
2. Writing a chemical equation – Read the paragraph on page 283 in the book.
Follow these rules when writing a chemical equation:
 Write the REACTANTS on the left side. Use a plus sign between molecules.
 Use an arrow to show what is produced in the reaction.
 Write the PRODUCTS of the reaction on the right side. Use a plus sign between molecules.
 Use numbers in front of molecular formulas to show how many molecules are involved in
the reaction (these numbers are the COEFFICIENTS). Do NOT use a one (1) as a
coefficient.
For this reaction:
2Al (s) + 6HCl (aq)  2AlCl3 (aq) + 3H2 (g)
What are the reactants? _________________________________________
What are the products? _________________________________________
How many molecules of HCl are involved in the reaction? ____ How many molecules of AlCl3 ___
How do you say what the arrow means? (see book) ______________________________________
What are the numbers in front of each compound called? __________________________________
What is the “physical state” of each of the compounds in the reaction? (see book)
Al _____________ HCl ______________ AlCl3 _______________ H2 _______________
What does the word “aqueous” mean? _________________________________________________
3. Write the chemical equation for the following chemical reactions. Include subscripts showing the
physical state of the compounds. Include coefficients showing the number of molecules of each
compound.
Example: 2 molecules of hydrogen gas (H2) react with one molecule of oxygen gas (O2) to yield
two molecules of water (H2O) vapor.
2H2 (g) + O2 (g)  2H2O (g)
a. 1 molecule of nitrogen gas (N2) reacts with 1 molecule of oxygen gas (O2) to yield 2 molecules of
nitrogen monoxide gas (NO)
________________________________________________________________________________
b. 1 molecule of sodium hydroxide (NaOH) reacts with 1 molecule of hydrochloric acid (HCl) to
yield 1 molecule of sodium chloride (NaCl) and 1 molecule of water (H2O). All reactants and
products are in a water solution.
________________________________________________________________________________
c. 1 molecule of solid zinc metal (Zn) reacts with 1 molecule of solid sulfur (S) to yield 1 molecule
of solid zinc sulfide (ZnS)
________________________________________________________________________________
4. For the following reaction:
2Al (s) + 6HCl (aq)  2AlCl3 (aq) + 3H2 (g)
Count the atoms of each element in the reactants and in the products:
Reactants
Products
Write a statement about what you found out:
Al
_______
_______
H
_______
_______
Cl
_______
_______
_____________________________________________________
_____________________________________________________
_____________________________________________________
Look up the “Law of Conservation of Mass” . What does it say? ____________________________
________________________________________________________________________________
Is the law obeyed in the reaction above? _____ Why do you say that? ________________________
________________________________________________________________________________