In the soilution below why is the value of K 6.7478 and not 6.7478 * 1015     Question Calculate ΔG° and K (at 298K) for this reaction: 2H2S(g) + SO2(g) ↔ 3S(s) + 2H2O(g) Expert Answer     Step 1 The standard Gibbs free energy can be calculated as follows: ∆G∘=nΣ∆G∘(Products)−mΣ∆G∘(Reactants)   where ΔGo: Standard Gibbs free energy n and m are stoichiometric coefficients and Equilibrium Constant (K) can be calculated as follows: ∆G∘=−RTlnK   where R: Gas Constant (8.314 JK-1mol-1) ΔGo: Standard Gibbs free energy K: Equilibrium Constant T: Temperature (298 K) Step 2 The standard Gibbs free energy of formation for the following substances are: ΔGof (H2S) = -33.4 kJ/mol ΔGof (SO2) = -300.1 kJ/mol ΔGof (S) = 0 kJ/mol ΔGof (H2O) = -228.6 kJ/mol Substituting all these values in this equation- ∆G∘======[3∆Gf∘(S)+2∆Gf∘(H2O)]−[2∆Gf∘(H2S)+1∆Gf∘(SO2)][3(0 kJ/mol)+2(−228.6 kJ/mol)]−[2(−33.4 kJ/mol)+1(−300.1 kJ/mol)][0 −457.2] kJ/mol−[−66.8−300.1] kJ/mol−457.2−[−366.9] kJ/mol−457.2+366.9 kJ/mol−90.3 kJ/mol   Now, equilibrium constant (K) can be calculated as: ∆G∘=−RTlnK   substitute all values in this equation as- −90.3 kJ/mol−90.3 kJ/mollnKlnKKK======−8.314×10−3kJK−1 mol−1×298 K×lnK−2.4775 kJ/mol×lnK−90.3 kJ/mol−2.4775 kJ/mol36.4480e36.44806.7478   Step 3 The value of ΔGo is -90.3 kJ/mol and the K value is 6.7478 for this reaction.

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Chapter17: Spontaneity, Entropy, And Free Energy
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Problem 7RQ: If you calculate a value for G for a reaction using the values of Gf in Appendix 4 and get a...
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In the soilution below why is the value of K 6.7478 and not 6.7478 * 1015

 

 

Question

Calculate ΔG° and K (at 298K) for this reaction:

2H2S(g) + SO2(g) ↔ 3S(s) + 2H2O(g)


Expert Answer

 
 
Step 1

The standard Gibbs free energy can be calculated as follows:

∆G∘=nΣ∆G∘(Products)−mΣ∆G∘(Reactants)

 

where

ΔGo: Standard Gibbs free energy

n and m are stoichiometric coefficients

and Equilibrium Constant (K) can be calculated as follows:

∆G∘=−RTlnK

 

where

R: Gas Constant (8.314 JK-1mol-1)

ΔGo: Standard Gibbs free energy

K: Equilibrium Constant

T: Temperature (298 K)

Step 2

The standard Gibbs free energy of formation for the following substances are:

ΔGof (H2S) = -33.4 kJ/mol

ΔGof (SO2) = -300.1 kJ/mol

ΔGof (S) = 0 kJ/mol

ΔGof (H2O) = -228.6 kJ/mol

Substituting all these values in this equation-

∆G∘======[3∆Gf∘(S)+2∆Gf∘(H2O)]−[2∆Gf∘(H2S)+1∆Gf∘(SO2)][3(0 kJ/mol)+2(−228.6 kJ/mol)]−[2(−33.4 kJ/mol)+1(−300.1 kJ/mol)][0 −457.2] kJ/mol−[−66.8−300.1] kJ/mol−457.2−[−366.9] kJ/mol−457.2+366.9 kJ/mol−90.3 kJ/mol

 

Now, equilibrium constant (K) can be calculated as:

∆G∘=−RTlnK

 

substitute all values in this equation as-

−90.3 kJ/mol−90.3 kJ/mollnKlnKKK======−8.314×10−3kJK−1

mol−1×298 K×lnK−2.4775 kJ/mol×lnK−90.3 kJ/mol−2.4775 kJ/mol36.4480e36.44806.7478

 

Step 3

The value of ΔGis -90.3 kJ/mol and the K value is 6.7478 for this reaction.

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