Section 7: Double Displacement – Gas Producing Reactions

Chapter 6: Chemical Reactions

Learning Goals

Identify and write equations for gas evolution reactions.

Gas Producing ReactionsGases that are commonly produced are carbon dioxide, hydrogen cyanide, sulfur dioxide, ammonia, and hydrogen sulfide.

2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)

Gas Producing ReactionsMany gas producing reactions occur when a product from a double displacement reaction decomposes.

HNO3(aq) + Na2CO3(aq) → H2CO3(aq) +

NaNO3(aq)

H2O and

CO2

Gas Producing ReactionsBegin by writing a skeletal equation

that includes the reactants and products that form when the cation of each reactant combines with the anion of the other. HNO3(aq) + Na2CO3(aq) → H2CO3(aq) +

NaNO3(aq)

Gas Producing ReactionsYou must recognize that H2CO3(aq) decomposes into H2O(l) and CO2(g) and write the corresponding equation. HNO3(aq) + Na2CO3(aq) → H2O(l) +

CO2(aq) + NaNO3(aq)

Gas Producing ReactionsFinally, balance the equation.

2HNO3(aq) + Na2CO3(aq) → H2O(l) + CO2(aq) + 2NaNO3(aq)

Practice

Write chemical, complete ionic, and net ionic equations for each of the following reactions. Perchloric acid reacts with aqueous potassium carbonate, forming carbon dioxide gas and water.

Practice

Nitric acid reacts with aqueous sodium carbonate.

Practice

Aqueous hydrobromic acid reacts with aqueous potassium sulfite.