6 HCl (aq) + 4 KI (aq) + K2SeO3 (aq) → 2 I2 (s) + 6 KCl (aq) + Se (s hexagonal black) + 3 H2O (ℓ)

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Stoichiometry

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HCl            Mass: g  or Solution Volume: mL of Concentration: mol/L
KI             Mass: g  or Solution Volume: mL of Concentration: mol/L
K2SeO3         Mass: g  or Solution Volume: mL of Concentration: mol/L
I2             Mass: g
KCl            Mass: g  or Solution Volume: mL of Concentration: mol/L
Se             Mass: g
H2O            Mass: g

Enthalpy of Reaction

[2ΔHf(I2 (s)) + 6ΔHf(KCl (aq)) + 1ΔHf(Se (s hexagonal black)) + 3ΔHf(H2O (ℓ))] - [6ΔHf(HCl (aq)) + 4ΔHf(KI (aq)) + 1ΔHf(K2SeO3 (aq))]
[2(0) + 6(-419.55) + 1(0) + 3(-285.83)] - [6(-167.15) + 4(-307.59) + 1(-1013.99)] = -127.54 kJ
-127.54 kJ     (exothermic)

Entropy Change

[2ΔSf(I2 (s)) + 6ΔSf(KCl (aq)) + 1ΔSf(Se (s hexagonal black)) + 3ΔSf(H2O (ℓ))] - [6ΔSf(HCl (aq)) + 4ΔSf(KI (aq)) + 1ΔSf(K2SeO3 (aq))]
[2(116.14) + 6(158.98) + 1(42.44) + 3(69.91)] - [6(56.48) + 4(213.79) + 1(217.55)] = 26.74 J/K
26.74 J/K     (increase in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(I2 (s)) + 6ΔGf(KCl (aq)) + 1ΔGf(Se (s hexagonal black)) + 3ΔGf(H2O (ℓ))] - [6ΔGf(HCl (aq)) + 4ΔGf(KI (aq)) + 1ΔGf(K2SeO3 (aq))]
[2(0) + 6(-414.55) + 1(0) + 3(-237.18)] - [6(-131.25) + 4(-334.89) + 1(-936.47)] = -135.31 kJ
-135.31 kJ     (spontaneous)

From ΔG = ΔH - TΔS:
-135.51 kJ     (spontaneous)

Equilibrium Constant, K (at 298.15 K)

5.08868343175936E+23
This process is favorable at 25°C.