9.5: Classifying Chemical Reactions- Take Two
- Page ID
- 451550
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Classify a chemical reaction as a precipitation reaction, neutralization reaction, or redox reaction.
In the previous section, we classified chemical reactions according to the pattern of how the atoms rearranged. Another way to classify reactions is based on the types of products and reactants. We will examine three types of reactions in this manner: precipitation reactions, neutralization reactions, and redox reactions. A brief introduction to each type of reaction is given bellow, followed by a page looking at the type of more reaction in more depth.
Precipitation Reactions
In a precipitation reaction, the reactants are two aqueous (soluble) ionic compounds. One of the products is an insoluble ionic compound; the second product is an ionic compound that remains aqueous. When aqueous solutions of potassium iodide and lead (II) nitrate are mixed, the following reaction occurs:
\[2 \ce{KI} \left( aq \right) + \ce{Pb(NO_3)_2} \left( aq \right) \rightarrow 2 \ce{KNO_3} \left( aq \right) + \ce{PbI_2} \left( s \right) \label{eq10}\]
There are very strong attractive forces that occur between \(\ce{Pb^{2+}}\) and \(\ce{I^-}\) ions and the result is a brilliant yellow precipitate (Figure \(\PageIndex{3}\)). The other product of the reaction, potassium nitrate, remains soluble.
_iodide_precipitating_out_of_solution.jpg?revision=1&size=bestfit&width=194&height=240)
Here are several more examples of precipitation reactions. Notice that the pattern of two soluble ionic compounds reacting to form a insoluble ionic compound and a soluble ionic compounds is repeated in each reactions. Also notice that the order of products is arbitrary: the insoluble ionic compound can be written as the first product or as the second product.
\[ \ce{BaCl_2} \left( aq \right) + \ce{Na_2SO_4} \left( aq \right) \rightarrow 2 \ce{NaCl} \left( aq \right) + \ce{BaSO_4} \left( s \right) \]
\[ \ce{Cu(NO_3)_2} \left( aq \right) + \ce{Na_2CO_3} \left( aq \right) \rightarrow \ce{CuCO_3} \left( s \right) + 2\ce{NaNO_3} \left( aq \right) \]
\[3 \ce{NaOH} \left( aq \right) + \ce{AlCl_3} \left( aq \right) \rightarrow \ce{Al(OH)_3} \left( s \right) + 3\ce{NaCl} \left( aq \right)\]
Neutralization Reactions
The reactants in a neutralization reaction are an acid and a hydroxide salt (another name for any ionic compound that contains hydroxide ions). One of the products is always water, and the other is a new ionic compound. Notice in the following examples that the hydroxide salt can be either solid or aqueous and that the order of both the reactants and the products is arbitrary.
\[\ce{HCl} \left( aq \right) + \ce{NaOH} \left( aq \right) \rightarrow \ce{NaCl} \left( aq \right) + \ce{H_2O} \left( l \right)\]
\[2\ce{KOH} \left( s \right) + \ce{H_2SO_4} \left( aq \right) \rightarrow \ce{K_2SO_4} \left( aq \right) + 2\ce{H_2O} \left( l \right)\]
\[\ce{Ba(OH)_2} \left( aq \right) + 2\ce{HNO_3} \left( aq \right) \rightarrow 2\ce{H_2O} \left( l \right) + \ce{BaSO_4} \left( aq \right)\]
Redox Reactions (Oxidation-Reduction Reactions)
To simplify discussion of this complex topic, we will only look at redox reactions in which an atom appears in its elemental form on one side of a reaction and as part of a compound on the other side of the reaction. The reaction of heptane and oxygen gives water vapor and carbon dioxide:
\[\ce{C_7H_16} \left( l \right) + 11\ce{O_2} \left( g \right) \rightarrow 7\ce{CO_2} \left( g \right) + 8\ce{H_2O} \left( g \right)\]
To identify this as a redox reaction, focus on the oxygen atoms. On the reactant side, they appear in the form of elemental oxygen. On the product side, they appear in two compounds: carbon dioxide and water.
In the examples that follow notice that the elements may be monoatomic or diatomic They may appear as products or reactants. There may also be two or more types of atoms transitioning from their elemental form to part of a compound (or vice versa). Also, you do not need to pay attention to the phase labels when identifying a redox reaction.
\[2 \ce{Na} \left( s \right) + \ce{Cl_2} \left( g \right) \rightarrow 2 \ce{NaCl} \left( s \right) \]
\[2 \ce{CO} \left( g \right) + \ce{O_2} \left( g \right) \rightarrow 2 \ce{CO_2} \left( g \right)\]
\[2 \ce{HgO} \left( s \right) \rightarrow 2 \ce{Hg} \left( l \right) + \ce{O_2} \left( g \right)\]
\[\ce{Zn} \left( s \right) + 2 \ce{HCl} \left( aq \right) \rightarrow \ce{ZnCl_2} \left( aq \right) + \ce{H_2} \left( g \right)\]