Balancing Chemical Equations Test Questions

Balancing chemical equations is a basic skill in chemistry. This collection of 10 chemistry test questions tests your ability to balance a chemical reaction. These equations will be balanced for mass. Other tests are available if you're practicing balancing equations for both mass and charge.

Question 1

Chemistry flasks with colored liquids — A balanced equation has the same number and type of atoms on both sides of the equation. Steve McAlister, Getty Images

__ AgI + __ Na

S + __ NaI

Question 2

__ Ba

Question 3

__ CaCl

+ __ NaCl

Question 4

__ FeS + __ O

Question 5

__ PCl

₅₂₃₄

+ __ HCl

Question 6

__ As + __ NaOH → __ Na

Question 7

__ Hg(OH)

Question 8

__ HClO

Question 9

__ CO + __ H

Question 10

__ KClO

+ __ KCl

Answers

1. 2 AgI + 1 Na₂S → 1 Ag₂S + 2 NaI
2. 1 Ba₃N₂ + 6 H₂O → 3 Ba(OH)₂ + 2 NH₃
3. 3 CaCl₂ + 2 Na₃PO₄ → 1 Ca₃(PO₄)₂ + 6 NaCl
4. 4 FeS + 7 O₂ → 2 Fe₂O₃ + 4 SO₂
5. 1 PCl₅ + 4 H₂O → 1 H₃PO₄ + 5 HCl
6. 2 As + 6 NaOH → 2 Na₃AsO₃ + 3 H₂
7. 3 Hg(OH)₂ + 2 H₃PO₄ → 1 Hg₃(PO₄)₂ + 6 H₂O
8. 12 HClO₄ + 1 P₄O₁₀ → 4 H₃PO₄ + 6 Cl₂O₇
9. 8 CO + 17 H₂ → 1 C₈H₁₈ + 8 H₂O
10. 10 KClO₃ + 3 P₄ → 3 P₄O₁₀ + 10 KCl

Tips for Balancing Equations

When balancing equations, remember the number of atoms of each element needs to be the same on both sides of the equation.
The coefficients (numbers in front of a species) are multiplied by every atom in that chemical.
The subscripts are multiplied only by the affected atom.
To start balancing, begin with less-common elements, like metal atoms or oxygen, and leave hydrogen atoms for last (they are usually the easiest to balance.
Be sure to check your work! Make a tally of all the atoms of each element on each side of the equation. Are they the same? Good! If not, go back and rework the coefficients and subscripts.
Although this test did not cover it, it's good practice to indicate the state of matter for each chemical species (s for solid, l for liquid, g for gas, and aq for a species in aqueous solution).