2HSCN + 2e− → SCN− + H2S↑ + CN−
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- Reduction of thiocyanic acid
Reduction of thiocyanic acid yields thiocyanate ion, hydrogen sulfide, and cyanide ion (Other reactions are here). This reaction is an oxidation-reduction reaction and is classified as follows:
Table of contents
Reaction data
Chemical equation
- Reduction of thiocyanic acid
General equation
- Reduction of reducible species
- ReactantOxidizing agent + e− ⟶ ProductReduction product
Oxidation state of each atom
- Reduction of thiocyanic acid
Reactants
| Chemical formula | Name | Coefficient | Type | Type in general equation |
|---|---|---|---|---|
| HSCN | Thiocyanic acid | 2 | Oxidizing | – |
| e− | Electron | 2 | – | Electron |
Products
| Chemical formula | Name | Coefficient | Type | Type in general equation |
|---|---|---|---|---|
| SCN− | Thiocyanate ion | 1 | – | – |
| H2S | Hydrogen sulfide | 1 | – | – |
| CN− | Cyanide ion | 1 | Reduced | – |
Thermodynamic changes
Changes in aqueous solution (1)
- Reduction of thiocyanic acid◆
ΔrG 46.1 kJ/mol K 0.84 × 10−8 pK 8.08
| Standard enthalpy of reaction ΔrH° kJ · mol−1 | Standard Gibbs energy of reaction ΔrG° kJ · mol−1 | Standard entropy of reaction ΔrS° J · K−1 · mol−1 | Standard heat capacity of reaction at constant pressure ΔrCp° J · K−1 · mol−1 | |
|---|---|---|---|---|
per 1 mol of Equation | 53.5 | 46.1 | 155.6 | – |
per 1 mol of | 26.8 | 23.1 | 77.80 | – |
per 1 mol of Electron | 26.8 | 23.1 | 77.80 | – |
per 1 mol of Thiocyanate ion | 53.5 | 46.1 | 155.6 | – |
per 1 mol of | 53.5 | 46.1 | 155.6 | – |
per 1 mol of Cyanide ion | 53.5 | 46.1 | 155.6 | – |
Changes in aqueous solution (2)
- Reduction of thiocyanic acid◆
ΔrG 51.9 kJ/mol K 0.81 × 10−9 pK 9.09
| Standard enthalpy of reaction ΔrH° kJ · mol−1 | Standard Gibbs energy of reaction ΔrG° kJ · mol−1 | Standard entropy of reaction ΔrS° J · K−1 · mol−1 | Standard heat capacity of reaction at constant pressure ΔrCp° J · K−1 · mol−1 | |
|---|---|---|---|---|
per 1 mol of Equation | 34.5 | 51.9 | 71 | – |
per 1 mol of | 17.3 | 25.9 | 36 | – |
per 1 mol of Electron | 17.3 | 25.9 | 36 | – |
per 1 mol of Thiocyanate ion | 34.5 | 51.9 | 71 | – |
per 1 mol of | 34.5 | 51.9 | 71 | – |
per 1 mol of Cyanide ion | 34.5 | 51.9 | 71 | – |
Changes in aqueous solution (3)
- Reduction of thiocyanic acid◆
ΔrG 36.4 kJ/mol K 0.42 × 10−6 pK 6.38
| Standard enthalpy of reaction ΔrH° kJ · mol−1 | Standard Gibbs energy of reaction ΔrG° kJ · mol−1 | Standard entropy of reaction ΔrS° J · K−1 · mol−1 | Standard heat capacity of reaction at constant pressure ΔrCp° J · K−1 · mol−1 | |
|---|---|---|---|---|
per 1 mol of Equation | – | 36.4 | – | – |
per 1 mol of | – | 18.2 | – | – |
per 1 mol of Electron | – | 18.2 | – | – |
per 1 mol of Thiocyanate ion | – | 36.4 | – | – |
per 1 mol of | – | 36.4 | – | – |
per 1 mol of Cyanide ion | – | 36.4 | – | – |
Changes in aqueous solution (4)
- Reduction of thiocyanic acid◆
ΔrG 42.2 kJ/mol K 0.40 × 10−7 pK 7.39
| Standard enthalpy of reaction ΔrH° kJ · mol−1 | Standard Gibbs energy of reaction ΔrG° kJ · mol−1 | Standard entropy of reaction ΔrS° J · K−1 · mol−1 | Standard heat capacity of reaction at constant pressure ΔrCp° J · K−1 · mol−1 | |
|---|---|---|---|---|
per 1 mol of Equation | – | 42.2 | – | – |
per 1 mol of | – | 21.1 | – | – |
per 1 mol of Electron | – | 21.1 | – | – |
per 1 mol of Thiocyanate ion | – | 42.2 | – | – |
per 1 mol of | – | 42.2 | – | – |
per 1 mol of Cyanide ion | – | 42.2 | – | – |
Thermodynamic data of reactants
| Chemical formula | Standard enthalpy of formation ΔfH° kJ · mol−1 | Standard Gibbs energy of formation ΔfG° kJ · mol−1 | Standard molar entropy S° J · K−1 · mol−1 | Standard molar heat capacity at constant pressure Cp° J · K−1 · mol−1 |
|---|---|---|---|---|
| HSCN (ai) | 76.44[1] | 92.71[1] | 144.3[1] | -40.2[1] |
| HSCN (ao) | – | 97.56[1] | – | – |
| e− | – | – | – | – |
* (ai):Ionized aqueous solution, (ao):Un-ionized aqueous solution
Thermodynamic data of products
| Chemical formula | Standard enthalpy of formation ΔfH° kJ · mol−1 | Standard Gibbs energy of formation ΔfG° kJ · mol−1 | Standard molar entropy S° J · K−1 · mol−1 | Standard molar heat capacity at constant pressure Cp° J · K−1 · mol−1 |
|---|---|---|---|---|
| SCN− (ao) | 76.44[1] | 92.71[1] | 144.3[1] | -40.2[1] |
| H2S (g) | -20.63[1] | -33.56[1] | 205.79[1] | 34.23[1] |
| H2S (ao) | -39.7[1] | -27.83[1] | 121[1] | – |
| CN− (ao) | 150.6[1] | 172.4[1] | 94.1[1] | – |
* (ao):Un-ionized aqueous solution, (g):Gas
References
List of references
- 1Janiel J. Reed (1989)The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI UnitsNational Institute of Standards and Technology (NIST)
- ^ ΔfH°, 76.44 kJ · mol−1
- ^ ΔfG°, 92.71 kJ · mol−1
- ^ S°, 144.3 J · K−1 · mol−1
- ^ Cp°, -40.2 J · K−1 · mol−1
- ^ ΔfG°, 97.56 kJ · mol−1
- ^ ΔfH°, 76.44 kJ · mol−1
- ^ ΔfG°, 92.71 kJ · mol−1
- ^ S°, 144.3 J · K−1 · mol−1
- ^ Cp°, -40.2 J · K−1 · mol−1
- ^ ΔfH°, -20.63 kJ · mol−1
- ^ ΔfG°, -33.56 kJ · mol−1
- ^ S°, 205.79 J · K−1 · mol−1
- ^ Cp°, 34.23 J · K−1 · mol−1
- ^ ΔfH°, -39.7 kJ · mol−1
- ^ ΔfG°, -27.83 kJ · mol−1
- ^ S°, 121. J · K−1 · mol−1
- ^ ΔfH°, 150.6 kJ · mol−1
- ^ ΔfG°, 172.4 kJ · mol−1
- ^ S°, 94.1 J · K−1 · mol−1