The extraction of metals from their oxides using carbon at high temperature involves number of important points. At a given pressure, a reaction is spontaneous if the Gibbs energy change is negative.
( Δ G = Δ H – T Δ S). Consider MO (s) ⎯→ M (s/ l ) + 
O 2(g)
The entropy change for this reaction is positive. On increasing the temperature this generally causes Δ G to become negative.
The variation of Δ G for
C (s) + O 2(g) ⎯→ CO 2(g) with increasing temperature is insignificant while for
C (s) + 
O 2 ⎯→ CO (g) , Δ G agains falls with increase in temperature. Δ G is state function.
Δ G° for formation for FeO (s) , CaO (s) and CrO (s) are -500 KJ/mole, –1300 KJ/mole and -700 KJ/mole at 25°C while for oxidation of C (gr) it remains practically -400 KJ/mole and starts becoming more and more negative after 700 K.
(i) Which of the following is theoretically reducible by C (s) at room temperature and 1 bar pressure –
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
(i)
Sol. Consider 2MO(s) + C(s) ⎯→ 2M (s) + CO 2(g)
(ii)
Sol. Δ G becomes more negative with temperature after 700K as most of the carbon now gets oxidized by C (s) + 
O 2 ⎯→ CO (g) and complete reaction can now be considered as MO (s) + C (s) ⎯→ M (s/ l ) + CO (g)
(iii)
Sol. Δ G becomes more negative for
MO (s) ⎯→ M (s/ l ) + 
O 2 (g)
as temperature is increased
Prepare Smarter with CGP Edu
Get practice questions, solutions, and test series in one place.
Write a Review
Share your experience with this question and solution.
Commentary
Send your comment, doubt, correction, or feedback to admin.
Similar Questions
Explore conceptually related problems