1. Chemical Equation Balancing
Practice Worksheet
By Daniel R. Barnes, this ppt init 2/9/2018
based on a much older worksheet

2. O O O O O Cl Cl Cl H H H H H 1.a. H2O 1.b. 2O2 two oxygen molecules
water molecule
1.c. 3HCl H H H Cl Cl Cl
three hydrogen chloride molecules

3. Cl- Cl- Cl- Cl- Cl- Cl- Cl- Cl- 1.d. 8NaCl Na+ Na+ Na+ Na+ Na+ Na+ Na+
8 formula units of sodium chloride

4. O C O C O C O C Cl Cl Cl Cl 1.e. 4CO2 4 carbon dioxide molecules
1.f. 3Cl2 Cl Cl Cl
3 chlorine molecules Cl

5. 2. Atom-counting
a. How many carbon atoms in CH4?
just one
b. How many oxygen atoms in 6CO2?
6 x 2 = 12
(multiply the coefficient times the subscript)
c. How many hydrogen atoms in 3(NH4)3PO4?
3 x 4 x 3 = 12 x 3 = 36
d. How many nitrogen atoms in 5(NH4)2SO4?
5 x 1 x 2 = 10

6. 3. Vocabulary
A chemical equation is made of at least two
formulas
and one arrow. The substances on the left of the arrow are the
reactants
and the substances on the right are the
products.

7. 4. Concepts
a. What never changes during a chemical reaction?
# of atoms of each element, any atom’s element,
# protons/neutrons, total mass, total energy
b. What DOES change during a chemical reaction?
who each atom is bonded to, chemical formulas, location of electrons, amount of stored “potential” energy
c. What is the difference between coefficients and subscripts?
Coefficients are full-sized and are placed in front of a formula.
Subscripts are little, lowered, and come after an element.
Coefficients can be changed when balancing an equation,
but subscripts can not.

8. 5. Balancing Equations
a H O2  H2O
H: H:
O: O: 2 2 2 4 2 4 2 1 2

9. 5. Balancing Equations
b CH O2  CO H2O
C: C:
H: H:
O: O: 2 2 1 1 4 2 4 2 4 3 4

10. 5. Balancing Equations
c NaOH HCl  NaCl H2O
Na: Na:
O: O:
H: H:
Cl: Cl: 1 1 1 1 2 2 1 1
If it isn’t broken . . .
don’t fix it.

11. 5. Balancing Equations
d V O2  V2O5
V: V:
O: O: 4 2 5 2 1 2 4 2 4 2 10 5 10
It’s totally legal to put an odd number over two in front of a diatomic element like O2.
In fact, chemists do it all the time.
Sometimes, though, it’s important to have only integers for your coefficients.
Notice that 5 x 2 = 2 x

12. 5. Balancing Equations
e C8H O2  CO H2O
C = C =
H = H =
O = O = 8 1 18 2 2 3
THIS SLIDE UNDER CONSTRUCTION . . .

13. 5. Balancing Equations
f NH4OH H2SO4  (NH4)2SO H2O
THIS SLIDE UNDER CONSTRUCTION . . .