The following reaction was described as the cause of sulfur deposits formed at volcanic sites:
It may also be used to remove SO, from powerplant stack gases. (a) Identify the type of
Interpretation:
The value of Kp, type of the given reaction, and whether the reaction is more or less effective at low temperature are to be determined, and the type of redox reaction is to be identified.
Concept introduction:
The disproportion reaction is a type of redox reaction. The compound of intermediate oxidation state converts into two different compounds, one is at a higher oxidation state and the other is at s lower oxidation state.
The relation between free energy change and standard free energy change is as follows:
Here,
At equilibrium the above equation is reduced to the expression:
The standard free energy change for the reaction is calculated using the following expression:
Here,
The standard enthalpy change of the reaction
Here,
The entropy changes of the system
The standard entropy change for this reaction is calculated using the expression as follows:
Here,
Answer to Problem 99AP
Solution:
a)
This is the reverse of a disproportion redox reaction.
b)
The value of the equilibrium constant for the given reaction is
c)
The reaction is less effective at high temperature.
Explanation of Solution
a) Type of redox reaction
The equation for the reaction of
Here, sulfur changes its oxidation state from
Thus, this reaction is the type of reverse disproportion reaction.
b) The equilibrium constant at
The equation for the reaction of
The standard free energy change for the reaction is calculated using the following expression:
Here,
The Gibbs energy for the reaction is as follows:
The standard free energy of formation of any element in its stable allotropic form at
From appendix
Substitute the values of the standard free energy of formation of the compound and
Therefore, standard free energy change for the reaction is
The equilibrium pressure constant is calculated using the expression as:
Here,
Substitute the values of
Therefore, the equilibrium constant for the given reaction is
c) Effectiveness of procedure at a high temperature
The equation for the reaction of
The standard enthalpy change of the system,
The standard enthalpy change of the reaction
Here,
The enthalpy change for the given reaction is as follows:
From appendix 2, the standard enthalpy changes for the formation of the substances are as follows:
Substitute the standard enthalpy change of the formation value of the substances in the above expression
The entropy changes of the system
The standard entropy change for this reaction is calculated using the expression as follows:
Here,
The entropy change for the reaction is as follows:
From appendix
Substitute the standard entropy values of the substances in the above expression
The standard Gibbs free energy change for the given reaction at temperature
Here,
Substitutes the value of
Therefore, standard Gibbs free energy change for the given reaction is
The change in entropy for this reaction is negative. The change in Gibbs free energy will become positive at high temperature. The reaction will be less effective at high temperature.
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Chapter 18 Solutions
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