Balanced Equations

Balanced equations can be written for the formation (synthesis) or decomposition of compounds. These balanced equations can then be used to determine the mass relationships among the chemicals in the reactions. Writing the balanced equations is the focus of the pages listed here. Working with the mass relationships is the subject of the next section.

Objective 9: From the name of a compound, write the balanced equation for its synthesis from the elements

This is a somewhat involved process, but very manageable if you take it step by step. First, note that synthesis means the formation of that compound. Since you are to start from the elements, you will need to figure out the proper formulas for the elements as well as the formula for the compound. Then follow through by balancing the equation. Remember the seven elements that are diatomic in elemental form!

Exercises

Write the balanced equation for synthesizing each of the following compounds, starting with the appropriate elements.

a. potassium bromide

b. aluminum oxide

c. iron (III) chloride

d. iron (II) chloride

e. dinitrogen pentoxide

f. chromium (VI) oxide

Answers

a. potassium bromide 2 K + Br₂ → 2 KBr

b. aluminum oxide 4 Al + 3 O₂ → 2 Al₂O₃

c. iron (III) chloride 2 Fe + 3 Cl₂ → 2 FeCl₃

d. iron (II) chloride Fe + Cl₂ → FeCl₂

e. dinitrogen pentoxide 2 N₂ + 5 O₂ → 2 N₂O₅

f. chromium (VI) oxide 2 Cr + 3 O₂ → 2 CrO₃

Objective 10: From the name of a compound, write the balanced equation for its decomposition into the elements

This objective is very much the same as the previous one. What's different is that we start with the compound and end up with the elements.

Exercises

Write the balanced equation for decomposing each of the following compounds into the appropriate elements.

a. sodium chloride

b. sulfur hexachloride

c. dinitrogen trioxide

d. aluminum sulfide

e. magnesium nitride

f. potassium iodide

g. chromium (III) oxide

Answers

a. sodium chloride 2 NaCl → 2 Na + Cl₂

b. sulfur hexachloride SCl₆ → S + 3 Cl₂

c. dinitrogen trioxide 2 N₂O₃ → 2 N₂ + 3 O₂

d. aluminum sulfide Al₂S₃ → 2 Al + 3 S

e. magnesium nitride Mg₃N₂ → 3 Mg + N₂

f. potassium iodide 2 KI → 2 K + I₂

g. chromium (III) oxide 2 Cr₂O₃ → 4 Cr + 3 O₂