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  3. 4(NH4)2Cr2O7 + 18e^− → 8NH3↑ + 3Cr + 8OH^− + 5CrO4^2−

4(NH4)2Cr2O7 + 18e− → 8NH3↑ + 3Cr + 8OH− + 5CrO42−

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Reduction of ammonium dichromate
4(NH4)2Cr2O7Ammonium dichromate + 18e−Electron
⟶
8NH3↑Ammonia + 3CrChromium + 8OH−Hydroxide ion + 5CrO42−Chromate ion

Reduction of ammonium dichromate yields ammonia, chromium, hydroxide ion, and chromate ion (Other reactions are here). This reaction is an oxidation-reduction reaction and is classified as follows:

Table of contents
  1. 1Reaction data
  2. 2Thermodynamic changes
  3. 3References
  4. 4Related reactions
  5. 5Related categories

Reaction data

Chemical equation

Reduction of ammonium dichromate
4(NH4)2Cr2O7Ammonium dichromate + 18e−Electron
⟶
8NH3↑Ammonia + 3CrChromium + 8OH−Hydroxide ion + 5CrO42−Chromate ion

General equation

Reduction of reducible species
ReactantOxidizing agent + e−
⟶
ProductReduction product

Oxidation state of each atom

Reduction of ammonium dichromate

Reactants

Chemical formulaNameCoefficientTypeType in general
equation
(NH4)2Cr2O7Ammonium dichromate4
Oxidizing
–
e−Electron18
–
Electron

Products

Chemical formulaNameCoefficientTypeType in general
equation
NH3Ammonia8
–
–
CrChromium3
Reduced
–
OH−Hydroxide ion8
–
–
CrO42−Chromate ion5
–
–

Thermodynamic changes

Changes in standard condition (1)

Reduction of ammonium dichromate
◆
ΔrG809.7 kJ/mol
K0.14 × 10−141
pK141.85
4(NH4)2Cr2O7Ionized aqueous solution + 18e−
⟶
8NH3↑Gas + 3CrCrystalline solid + 8OH−Un-ionized aqueous solution + 5CrO42−Un-ionized aqueous solution
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
406.2809.7−178.8–
101.5202.4−44.70–
per 1 mol of
Electron
22.5744.98−9.933–
per 1 mol of
50.77101.2−22.35–
per 1 mol of
135.4269.9−59.60–
per 1 mol of
Hydroxide ion
50.77101.2−22.35–
per 1 mol of
Chromate ion
81.24161.9−35.76–

Changes in standard condition (2)

Reduction of ammonium dichromate
◆
ΔrG729.3 kJ/mol
K0.17 × 10−127
pK127.77
4(NH4)2Cr2O7Ionized aqueous solution + 18e−
⟶
8NH3↑Un-ionized aqueous solution + 3CrCrystalline solid + 8OH−Un-ionized aqueous solution + 5CrO42−Un-ionized aqueous solution
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
132.8729.3−828.0–
33.20182.3−207.0–
per 1 mol of
Electron
7.37840.52−46.00–
per 1 mol of
16.6091.16−103.5–
per 1 mol of
44.27243.1−276.0–
per 1 mol of
Hydroxide ion
16.6091.16−103.5–
per 1 mol of
Chromate ion
26.56145.9−165.6–

Thermodynamic data of reactants

Chemical formulaStandard 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
(NH4)2Cr2O7 (cr)-1806.7[1]–––
(NH4)2Cr2O7 (ai)-1755.2[1]-1459.5[1]488.7[1]–
e−––––
* (cr):Crystalline solid, (ai):Ionized aqueous solution

Thermodynamic data of products

Chemical formulaStandard 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
NH3 (g)-46.11[1]-16.45[1]192.45[1]35.06[1]
NH3 (ao)-80.29[1]-26.50[1]111.3[1]–
Cr (cr)0[1]0[1]23.77[1]23.35[1]
Cr (g)396.6[1]351.8[1]174.50[1]20.79[1]
OH− (g)-143.5[1]–––
OH− (ao)-229.994[1]-157.244[1]-10.75[1]-148.5[1]
CrO42− (ao)-881.15[1]-727.75[1]50.21[1]–
* (g):Gas, (ao):Un-ionized aqueous solution, (cr):Crystalline solid

References

List of references

  1. 1
    Janiel J. Reed (1989)
    The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI Units
    National Institute of Standards and Technology (NIST)