Nickel metal reacts with carbon monoxide to form tetra-carbonyl nickel, Ni(CO)4:
This reaction is exploited in the Mond process in order to separate pure nickel from other metals. The reaction above separates nickel from impurities by dissolving it into the gas phase. Conditions are then changed so that the reaction runs in the opposite direction to recover the purified metal.
(a) Predict the sign of
(b) Use tabulated
(c) Find the range of temperatures at which this reaction is spontaneous in the forward direction.
Concept Introduction:
Gibb’s free energy is a state function which predicts whether a process is spontaneous or not at conditions of constant pressure and temperature. Gibb’s free energy change for a process at constant temperature is defined as:
Where
If a process is exothermic and entropy of the process decreases, that is
If a process is endothermic and entropy of the process increases, that is
Enthalpy change for a process is determined as:
Where v is for stoichiometric coefficients.
Similarly entropy change for a process is determined as:
Where v is for stoichiometric coefficients and
Similar to enthalpy and entropy, standard Gibb’s free energy change can be calculated as:
Also
Answer to Problem 10.88PAE
Solution:
a) The sign of
b)
c)
The reaction is spontaneous in the forward direction at temperatures below 392.3 K.
a)
Explanation of Solution
Entropy is defined as the measure of randomness or disorder in a system.
More number of particles would mean more random arrangements of particles of a system. And so entropy of any system increases if it moves towards more random distribution of particles constituting the system.
One way to increase entropy of a system is to increase the number of particles present. So a chemical reaction that would increase the number of moles of gas in the system would increase entropy.
Given reaction is:
The reactants have 4 moles of gas while the product has just one. Hence entropy of products is less than the reactants. Thus the sign of
b)
Given reaction is:
The thermodynamic enthalpies of formation for the compounds as tabulated are
Calculate enthalpy change the above reaction that is
The thermodynamic Gibb’s free emergies of formation for the compounds as tabulated are
Calculate enthalpy change the above reaction that is
Similarly, thermodynamic entropies for the compounds as tabulated are
Calculate enthalpy change the above reaction that is
c)
If a process is exothermic and entropy of the process decreases, that is
Calculate the temperature at which
The reaction is spontaneous in the forward direction at temperatures below 392.3 K.
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Chapter 10 Solutions
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