Skip to main content
Chemistry LibreTexts

5.8: Gas Evolution Reactions

  • Page ID
    369558
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Learning Objectives

    • Identify when a reaction will evolve a gas.

     

    Gas Evolving Reactions

    A gas evolution reaction is a chemical process that produces a gas, such as oxygen or carbon dioxide. In the following examples, an acid reacts with a carbonate, producing salt, carbon dioxide, and water, respectively. For example, nitric acid reacts with sodium carbonate to form sodium nitrate, carbon dioxide, and water (Table \(\PageIndex{1}\)):

    \[​\ce{2HNO3(aq)+Na2CO3(aq)→2NaNO3(aq)+CO2(g)+H2O(l)​}\]

    Sulfuric acid reacts with calcium carbonate to form calcium sulfate, carbon dioxide, and water:

    \[\ce{H2SO4(aq) + CaCO3(aq) → CaSO4(aq) + CO2(g)+H2O(l)}\]

    ​Hydrochloric acid reacts with calcium carbonate to form calcium chloride, carbon dioxide, and water:

    \[​\ce{2HCl(aq) + CaCO3(aq) → CaCl2(aq) + CO2(g) + H2O(l)}\]​

    Figure \(\PageIndex{1}\) demonstrates this type of reaction:

    Reaction setup with one test tube containing sodium carbonate and hydrochloric acid that's connected to by a tube to a second test tube containing limewater
    Figure \(\PageIndex{1}\): Reaction of acids with carbonates. In this reaction setup, lime water (water + calcium hydroxide) is poured into one of the test tubes and sealed with a stopper. A small amount of hydrochloric acid is carefully poured into the remaining test tube. A small amount of sodium carbonate is added to the acid, and the tube is sealed with a rubber stopper. The two tubes are connected. As a result of the acid-carbonate reaction, carbon dioxide is produced and the lime water turns milky.

    In this reaction setup, lime water, a dilute calcium hydroxide (\(Ca(OH)_2\)) solution, is poured into one of the test tubes and sealed with a stopper. A small amount of hydrochloric acid is carefully poured into the remaining test tube. A small amount of sodium carbonate is added to the acid, and the tube is sealed with a rubber stopper. The two tubes are connected. As a result of the acid-carbonate reaction, carbon dioxide is produced and the lime water turns milky.

     

    Table \(\PageIndex{1}\): Types of Compounds That Undergo Gas-Evolution Reactions
    Reactant Type Intermediate Product Gas Evolved Example
    sulfide none \(\ce{H2S}\) \(\ce{2HCl(aq) + K2S \rightarrow H2S (g) + 2KCl (aq)}\)
    carbonates and bicarbonates \(\ce{H2CO3}\) \(\ce{CO2}\) \(\ce{2HCl(aq) + K2CO2 \rightarrow H2O (l) + CO2(g) + 2KCl (aq)}\)
    sulfites and bisulfites \(\ce{H2SO3}\) \(\ce{SO2}\) \(\ce{2HCl(aq) + K2SO2 \rightarrow H2O (l) + SO2(g) + 2KCl (aq)}\)
    ammonia \(\ce{NH4OH}\) \(\ce{NH3}\) \(\ce{NH4Cl(aq) + KOH \rightarrow H2O (l) + NH3(g) + 2KCl (aq)}\)

     

    The gas-evolving experiment lime water is illustrated in the following video:

    Video \(\PageIndex{1}\): Carbon Dioxide (\(CO_2\)) & Limewater (Chemical Reaction). As the reaction proceeds, the limewater on the turns from clear to milky; this is due to the \(CO_2(g)\) reacting with the aqueous calcium hydroxide to form calcium carbonate, which is only slightly soluble in water.

    When this experiment is repeated with nitric or sulfuric acid instead of \(HCl\), it yields the same results: the clear limewater turns milky, indicating the production of carbon dioxide. Another method to chemically generate gas is the oxidation of metals in acidic solutions. This reaction will yield a metal salt and hydrogen gas.

    \[\ce{2HCl (aq) + Zn(s) \rightarrow ZnCl_2 (aq) + H_2 (g)}\]

    Here, hydrochloric acid oxidizes zinc to produce an aqueous metal salt and hydrogen gas bubbles. Recall that oxidation refers to a loss of electrons, and reduction refers to the gain of electrons. In the above redox reaction, neutral zinc is oxidized to \(Zn^{2+}\), and the acid, \(H^+\), is reduced to \(H_2(g)\). The oxidation of metals by strong acids is another common example of a gas evolution reaction.

    Contributors & Affiliations

    This page was constructed from content via the following contributor(s) and edited (topically or extensively) by the LibreTexts development team to meet platform style, presentation, and quality:


    5.8: Gas Evolution Reactions is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

    • Was this article helpful?