Skip to main content
Chemistry LibreTexts

13: The Phase Rule and Phase Diagrams

  • Page ID
    20414
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    \( \newcommand{\tx}[1]{\text{#1}}      % text in math mode\)
     \( \newcommand{\subs}[1]{_{\text{#1}}} % subscript text\)
     \( \newcommand{\sups}[1]{^{\text{#1}}} % superscript text\)
     \( \newcommand{\st}{^\circ}            % standard state symbol\)
     \( \newcommand{\id}{^{\text{id}}}      % ideal\)
     \( \newcommand{\rf}{^{\text{ref}}}     % reference state\)
     \( \newcommand{\units}[1]{\mbox{$\thinspace$#1}}\)
     \( \newcommand{\K}{\units{K}}  % kelvins\)
     \( \newcommand{\degC}{^\circ\text{C}} % degrees Celsius\)
     \( \newcommand{\br}{\units{bar}}  % bar (\bar is already defined)\)
     \( \newcommand{\Pa}{\units{Pa}}\)
     \( \newcommand{\mol}{\units{mol}}  % mole\)
     \( \newcommand{\V}{\units{V}}  % volts\)
     \( \newcommand{\timesten}[1]{\mbox{$\,\times\,10^{#1}$}}\)
     \( \newcommand{\per}{^{-1}}  % minus one power\)
     \( \newcommand{\m}{_{\text{m}}}  % subscript m for molar quantity\)
     \( \newcommand{\CVm}{C_{V,\text{m}}} % molar heat capacity at const.V\)
     \( \newcommand{\Cpm}{C_{p,\text{m}}} % molar heat capacity at const.p\)
     \( \newcommand{\kT}{\kappa_T} % isothermal compressibility\)
     \( \newcommand{\A}{_{\text{A}}}  % subscript A for solvent or state A\)
     \( \newcommand{\B}{_{\text{B}}}  % subscript B for solute or state B\)
     \( \newcommand{\bd}{_{\text{b}}}  % subscript b for boundary or boiling point\)
     \( \newcommand{\C}{_{\text{C}}}  % subscript C\)
     \( \newcommand{\f}{_{\text{f}}}  % subscript f for freezing point\)
     \( \newcommand{\mA}{_{\text{m},\text{A}}} % subscript m,A (m=molar)\)
     \( \newcommand{\mB}{_{\text{m},\text{B}}} % subscript m,B (m=molar)\)
     \( \newcommand{\mi}{_{\text{m},i}}        % subscript m,i (m=molar)\)
     \( \newcommand{\fA}{_{\text{f},\text{A}}} % subscript f,A (for fr. pt.)\)
     \( \newcommand{\fB}{_{\text{f},\text{B}}} % subscript f,B (for fr. pt.)\)
     \( \newcommand{\xbB}{_{x,\text{B}}}       % x basis, B\)
     \( \newcommand{\xbC}{_{x,\text{C}}}       % x basis, C\)
     \( \newcommand{\cbB}{_{c,\text{B}}}       % c basis, B\)
     \( \newcommand{\mbB}{_{m,\text{B}}}       % m basis, B\)
     \( \newcommand{\kHi}{k_{\text{H},i}}      % Henry's law constant, x basis, i\)
     \( \newcommand{\kHB}{k_{\text{H,B}}}      % Henry's law constant, x basis, B\)
     \( \newcommand{\arrow}{\,\rightarrow\,} % right arrow with extra spaces\)
     \( \newcommand{\arrows}{\,\rightleftharpoons\,} % double arrows with extra spaces\)
     \( \newcommand{\ra}{\rightarrow} % right arrow (can be used in text mode)\)
     \( \newcommand{\eq}{\subs{eq}} % equilibrium state\)
     \( \newcommand{\onehalf}{\textstyle\frac{1}{2}\D} % small 1/2 for display equation\)
     \( \newcommand{\sys}{\subs{sys}} % system property\)
     \( \newcommand{\sur}{\sups{sur}} % surroundings\)
     \( \renewcommand{\in}{\sups{int}} % internal\)
     \( \newcommand{\lab}{\subs{lab}} % lab frame\)
     \( \newcommand{\cm}{\subs{cm}} % center of mass\)
     \( \newcommand{\rev}{\subs{rev}} % reversible\)
     \( \newcommand{\irr}{\subs{irr}} % irreversible\)
     \( \newcommand{\fric}{\subs{fric}} % friction\)
     \( \newcommand{\diss}{\subs{diss}} % dissipation\)
     \( \newcommand{\el}{\subs{el}} % electrical\)
     \( \newcommand{\cell}{\subs{cell}} % cell\)
     \( \newcommand{\As}{A\subs{s}} % surface area\)
     \( \newcommand{\E}{^\mathsf{E}} % excess quantity (superscript)\)
     \( \newcommand{\allni}{\{n_i \}} % set of all n_i\)
     \( \newcommand{\sol}{\hspace{-.1em}\tx{(sol)}}\)
     \( \newcommand{\solmB}{\tx{(sol,$\,$$m\B$)}}\)
     \( \newcommand{\dil}{\tx{(dil)}}\)
     \( \newcommand{\sln}{\tx{(sln)}}\)
     \( \newcommand{\mix}{\tx{(mix)}}\)
     \( \newcommand{\rxn}{\tx{(rxn)}}\)
     \( \newcommand{\expt}{\tx{(expt)}}\)
     \( \newcommand{\solid}{\tx{(s)}}\)
     \( \newcommand{\liquid}{\tx{(l)}}\)
     \( \newcommand{\gas}{\tx{(g)}}\)
     \( \newcommand{\pha}{\alpha}        % phase alpha\)
     \( \newcommand{\phb}{\beta}         % phase beta\)
     \( \newcommand{\phg}{\gamma}        % phase gamma\)
     \( \newcommand{\aph}{^{\alpha}}     % alpha phase superscript\)
     \( \newcommand{\bph}{^{\beta}}      % beta phase superscript\)
     \( \newcommand{\gph}{^{\gamma}}     % gamma phase superscript\)
     \( \newcommand{\aphp}{^{\alpha'}}   % alpha prime phase superscript\)
     \( \newcommand{\bphp}{^{\beta'}}    % beta prime phase superscript\)
     \( \newcommand{\gphp}{^{\gamma'}}   % gamma prime phase superscript\)
     \( \newcommand{\apht}{\small\aph} % alpha phase tiny superscript\)
     \( \newcommand{\bpht}{\small\bph} % beta phase tiny superscript\)
     \( \newcommand{\gpht}{\small\gph} % gamma phase tiny superscript\)

    \( \newcommand{\upOmega}{\Omega}\)

     \( \newcommand{\dif}{\mathop{}\!\mathrm{d}}   % roman d in math mode, preceded by space\)
     \( \newcommand{\Dif}{\mathop{}\!\mathrm{D}}   % roman D in math mode, preceded by space\)
     \( \newcommand{\df}{\dif\hspace{0.05em} f} % df\)

     \(\newcommand{\dBar}{\mathop{}\!\mathrm{d}\hspace-.3em\raise1.05ex{\Rule{.8ex}{.125ex}{0ex}}} % inexact differential \)
     \( \newcommand{\dq}{\dBar q} % heat differential\)
     \( \newcommand{\dw}{\dBar w} % work differential\)
     \( \newcommand{\dQ}{\dBar Q} % infinitesimal charge\)
     \( \newcommand{\dx}{\dif\hspace{0.05em} x} % dx\)
     \( \newcommand{\dt}{\dif\hspace{0.05em} t} % dt\)
     \( \newcommand{\difp}{\dif\hspace{0.05em} p} % dp\)
     \( \newcommand{\Del}{\Delta}\)
     \( \newcommand{\Delsub}[1]{\Delta_{\text{#1}}}\)
     \( \newcommand{\pd}[3]{(\partial #1 / \partial #2 )_{#3}} % \pd{}{}{} - partial derivative, one line\)
     \( \newcommand{\Pd}[3]{\left( \dfrac {\partial #1} {\partial #2}\right)_{#3}} % Pd{}{}{} - Partial derivative, built-up\)
     \( \newcommand{\bpd}[3]{[ \partial #1 / \partial #2 ]_{#3}}\)
     \( \newcommand{\bPd}[3]{\left[ \dfrac {\partial #1} {\partial #2}\right]_{#3}}\)
     \( \newcommand{\dotprod}{\small\bullet}\)
     \( \newcommand{\fug}{f} % fugacity\)
     \( \newcommand{\g}{\gamma} % solute activity coefficient, or gamma in general\)
     \( \newcommand{\G}{\varGamma} % activity coefficient of a reference state (pressure factor)\)
     \( \newcommand{\ecp}{\widetilde{\mu}} % electrochemical or total potential\)
     \( \newcommand{\Eeq}{E\subs{cell, eq}} % equilibrium cell potential\)
     \( \newcommand{\Ej}{E\subs{j}} % liquid junction potential\)
     \( \newcommand{\mue}{\mu\subs{e}} % electron chemical potential\)
    \( \newcommand{\defn}{\,\stackrel{\mathrm{def}}{=}\,} % "equal by definition" symbol\)

     \( \newcommand{\D}{\displaystyle} % for a line in built-up\)
     \( \newcommand{\s}{\smash[b]} % use in equations with conditions of validity\)
     \( \newcommand{\cond}[1]{\\[-2.5pt]{}\tag*{#1}}\)
     \( \newcommand{\nextcond}[1]{\\[-5pt]{}\tag*{#1}}\)
     \( \newcommand{\R}{8.3145\units{J$\,$K$\per\,$mol$\per$}}     % gas constant value\)
     \( \newcommand{\Rsix}{8.31447\units{J$\,$K$\per\,$mol$\per$}} % gas constant value - 6 sig figs\)

    \( \newcommand{\jn}{\hspace3pt\lower.3ex{\Rule{.6pt}{2ex}{0ex}}\hspace3pt} \)
    \( \newcommand{\ljn}{\hspace3pt\lower.3ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise.45ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise1.2ex{\Rule{.6pt}{.5ex}{0ex}} \hspace3pt} \)
    \( \newcommand{\lljn}{\hspace3pt\lower.3ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise.45ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise1.2ex{\Rule{.6pt}{.5ex}{0ex}}\hspace1.4pt\lower.3ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise.45ex{\Rule{.6pt}{.5ex}{0ex}}\hspace-.6pt\raise1.2ex{\Rule{.6pt}{.5ex}{0ex}}\hspace3pt} \) 

    We encountered the Gibbs phase rule and phase diagrams in Chapter 8 in connection with single-substance systems. The present chapter derives the full version of the Gibbs phase rule for multicomponent systems. It then discusses phase diagrams for some representative types of multicomponent systems, and shows how they are related to the phase rule and to equilibrium concepts developed in Chapters 11 and 12.


    This page titled 13: The Phase Rule and Phase Diagrams is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Howard DeVoe via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.