Use the terms in the boxes to fill in the blanks in the following paragraphs.
Atoms
Correct
Mass
Balanced
Element
Mg
Chemical Reaction
Equation
Numbers
Coefficients
Formula
Products
Reactants
Substance
Two
Yields
A ___________________________ is a well defined example of a chemical change. A chemical
___________________________ can be used to show the changes that occur in a chemical reaction. In a
chemical reaction, the substance on the left side of the arrow are the starting substance. These substances are
called ___________________________. The substances on the right side of the arrow are the substances that
result from the reaction. These substances are called ___________________________. The arrow is read as
either produces or ___________________________.
According to the law of conservation of ___________________________, atoms are neither lost nor
gained during a chemical reaction. This law is illustrated when a chemical equation is ___________________.
When this is done, there will be the same number of ___________________________ of each kind on both
sides of the equation.
In a chemical equation, the numbers that are placed in front of the symbols and the formulas are called
___________________________. They are necessary to keep the ___________________________ of atoms
in balance.
There are several rules for balancing an equation. First, write the correct _________________________
for each reactant and product. Next, choose the coefficients that make the number of atoms of each
___________________________ on each side of the equation equal. The correctly written formula should not
be changed. If you change the formula of a substance, the equation is no longer ________________________.
Changing a formula will indicate a ___________________________ different than the one intended.
To balance the equation Mg + O2  MgO, first choose coefficients to make the number of atoms of
each element on each side of the equation equal. You would need to place a coefficient of
___________________________ in front of the product MgO. You would also need to place a coefficient of
two in front of the reactant ___________________________.
Use the equations to answer the questions.
Zn + S  ZnS
1. What are the reactant(s) in this chemical equation? __________________________________________
2. What are the product(s) in this chemical equation? __________________________________________
3. According to the law of conservation of mass, if the total mass of the product in this chemical reaction is
14 grams, what must be the combined masses of the reactants be? ______________________________
2H2 + O2  2H2O
4. What are the reactant(s) in this chemical equation? __________________________________________
5. What are the product(s) in this chemical equation? __________________________________________
6. What do the coefficients tell you about the ratio of reactants? _________________________________
__________________________________________________________________________________
7. How many units of product are produced? ________________________________________________
Write the chemical equations for the following reactions.
8. Two units of sodium plus one unit of chlorine gas produce two units of sodium chloride.
__________________________________________________________________________________
9. One unit of methane (CH4), plus two units of oxygen (O2) produce one unit of carbon dioxide (CO2) and
two units of water. ___________________________________________________________________
10. One unit of aluminum sulfate plus three units of barium chloride yield two units of aluminum chloride
plus three units of barium sulfate. _______________________________________________________
Label the parts of the equation using the following words: Coefficient, Reactants, Products, Subscripts, Yields.
2 K + MgBr2  2KBr + Mg
Classify the following chemical reactions as: Synthesis, Decomposition, Single Displacement, or Double
Displacement.
_______________________________________ 2H2 + O2  2H2O
_______________________________________ 2H2O  2H2 + O2
_______________________________________ Zn + H2SO4  ZnSO4 + H2
_______________________________________ 2CO + O2  2CO2
_______________________________________ 2HgO  2Hg + O2
_______________________________________ 2KBr + Cl 2  2KCl + Br2
_______________________________________ CaO + H2O  Ca(OH)2
_______________________________________ AgNO3 + NaCl  AgCl + NaNO3
_______________________________________ 2H2O2  2H2O + O2
_______________________________________ Ca(OH)2 + H2SO4  CaSO4 + 2H2O
True/False. Write out the word “true” or “false” for each statement.
____________________The new substances formed as a result of a chemical reaction are called products.
____________________The law of conservation of mass states that mass is neither created nor destroyed in a
chemical reaction.
____________________A chemical equation must be balanced in order to show that mass is conserved during
a reaction.
____________________Because the equation N2H4 + O2N2+H2O has two nitrogen atoms on each side, the
equation is balanced.
____________________A decomposition reaction is the opposite of a synthesis reaction.
____________________A combustion reaction is a reaction in which a substance reacts with carbon dioxide,
often producing heat and light.
____________________The reaction that forms water can be classified as either a synthesis reaction or a
combustion reaction.
____________________The formation of chemical bonds absorbs energy.
____________________In exothermic reaction, the energy required to break the bonds in the reactants is
greater than the energy released as the products form.