Chemical Thermodynamics Question 390
Question: The factor of $ \Delta G $ values is important in metallurgy. The $ \Delta G $ values for the following reactions at $ {{800}^{{}^\circ }}C $ are given as:
$ S_2( s )+2O_2( g )\xrightarrow{{}}2SO_2( g );\Delta G=-544kJ $
$ 2Zn( s )+S_2( s )\xrightarrow{{}}2ZnS( s );\Delta G=-293kJ $
$ 2Zn( s )+O_2( g )\xrightarrow{{}}2ZnO( s );\Delta G=-480kJ $
Then $ \Delta G $ for the reaction: $ 2ZnS(s)+3O_2(g)\xrightarrow{{}}2ZnO(s)+2SO_2(g) $ will be:
Options:
A) $ -357kJ $
B) $ -731kJ $
C) $ -773kJ $
D) $ -229kJ $
Show Answer
Answer:
Correct Answer: B
Solution:
- For the reaction $ 2,ZnS\to 2,Zn+S_2:\Delta G_1^{{}^\circ }=293kJ $ ………(i) $ 2,Zn+O_2\to 2,ZnO;\Delta G_2^{{}^\circ }=-480kJ $ ……….(ii) $ S_2+2O_2\to 2SO_2;\Delta G{ _3}^{{}^\circ }=-544kJ $ ………(iii) $ \Delta {{G}^{{}^\circ }} $ for the reaction $ 2ZnS+3O_2\to 2ZnO+2SO_2 $ can be obtained by adding eqn. (i), (ii) and (iii)
$ \Rightarrow \Delta G{}^\circ =293-480-544=-731kJ $
