Do you Know the Basics Quiz
Atoms, Molecules and Recognizing Balanced Equations
If the equations are balanced, circle them. If they are not balanced, explain how you know they
are not balanced in the space below the equation.
1. Mg + 2HCl
MgCl2 + H2
2. H2 + O2
H2O
This equation is not balanced because there are two atoms of oxygen on the reactants side and
only one on the products side.
3. Cu + H2SO4
CuSO4 + H2
4. Fe + S
Fe2S3
This equation is not balanced because there are only one atom of iron and one atom of sulfur on
the reactants side, but two atoms of iron and three of sulfur on the products side.
5. N2 + 3H2
6. AlN
2NH3
Al + N2
This equation is not balanced because there is only one atom of nitrogen on the reactants side,
but two atoms of nitrogen on the products side.
How many different kinds of molecules are in the equation below? List them and tell the
numbers of each.
7. Mg(OH)2 + 2HCl
Molecule
Mg(OH)2
HCl
MgCl2
H20
MgCl2 + H2O
How Many
One
Two
One
One
How many different kinds of ATOMS are in the chemical equation below? List them and tell
the number found on each side of the equation.
8. 2 K + 2H2O
H2 + 2KOH
ATOM
NUMBER
K (Potassium)
2
H (Hydrogen)
4
O (Oxygen)
2
9. In chemical reactions one or more new substances are created.
Are new atoms created? ___No________ Justify your answer below.
According to the law of conservation of mass, matter cannot be gained or lost in a chemical
reaction. Atoms that go in, must come out. Students may give evidence saying that the numbers
and types of atoms are the same on both sides of the equation.
In all of these reactions, the bonds that hold one atom to another in the reactants are broken, the
atoms rearrange themselves, and bond together in new ways to form the products.
10. What is the difference between reactants and products in a chemical reaction?
Reactants are the molecules that go into a chemical reaction. They are changed (the atoms are
rearranged) in the reaction to form products.
11. What is the difference between an element and a compound?
Elements are pure substances made out of one single kind of atom. They can be found on the
periodic table. Compounds are chemicals made out of two or more different types of atoms
bonded together to form a new substance.