16.7: Standard Molar Entropies
- Page ID
- 49567
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Because the entropy of a substance depends on the amount of substance, the pressure, and the temperature, it is convenient to describe the entropy of a substance in terms of Sm°, its standard molar entropy, i.e., as the entropy of 1 mol of substance at the standard pressure of 1 atm (101.3 kPa) and given temperature. Values of the standard molar entropies of various substances at 298 K (25°C) are given in the table. A table like this can be used in much the same way as a table of standard enthalpies of formation in order to find the entropy change ΔSm° for a reaction occurring at standard pressure and at 298 K.
Table \(\PageIndex{1}\) The Standard Molar Entropies of Selected Substances at 298.15 K (25°C)
| Compound | Smo /J K-1mol-1 | Compound | Smo /J K-1mol-1 |
| Solids | Diatomic Gases | ||
| C (diamond) | 2.377 | ||
| C (graphite) | 5.74 | H2 | 130.7 |
| Si | 18.8 | D2 | 145.0 |
| Ge | 31.1 | HCl | 186.9 |
| Sn (gray) | 44.1 | HBr | 198.7 |
| Pb | 64.8 | HI | 206.6 |
| Li | 29.1 | N2 | 191.6 |
| Na | 51.2 | O2 | 205.1 |
| K | 64.2 | F2 | 202.8 |
| Rb | 69.5 | Cl2 | 223.1 |
| Cs | 85.2 | Br2 | 245.5 |
| NaF | 51.5 | I2 | 260.7 |
| MgO | 26.9 | CO | 197.7 |
| AlN | 20.2 | Triatomic Gases | |
| NaCl | 72.1 | H2O | 188.8 |
| KCl | 82.6 | NO2 | 240.1 |
| Mg | 32.7 | H2S | 205.8 |
| Ag | 42.6 | CO2 | 213.7 |
| I2 | 116.1 | SO2 | 248.2 |
| MgH2 | 31.1 | N2O | 219.9 |
| AgN3 | 99.2 | O3 | 238.9 |
| Liquids | Polyatomic Gases( > 3) | ||
| Hg | 76.0 | CH4 | 186.3 |
| Br2 | 152.2 | C2H6 | 229.6 |
| H2O | 69.9 | C3H8 | 269.9 |
| H2O2 | 109.6 | C4H10 | 310.2 |
| CH3OH | 126.8 | C5H12 | 348.9 |
| C2H5OH | 160.7 | C2H4 | 219.6 |
| C6H6 | 172.8 | N2O4 | 304.3 |
| BCl3 | 206.3 | B2H6 | 232.0 |
| Monatomic Gases | BF3 | 254.0 | |
| He | 126.0 | NH3 | 192.5 |
| Ne | 146.2 | ||
| Ar | 154.8 | ||
| Kr | 164.0 | ||
| Xe | 169.6 | ||