16.7: Standard Molar Entropies
- Page ID
- 49567
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 |