Ncert Solutions Chemistry Class 12th

The free energy formation ( Δ_fG^o ) of CO from C becomes lower at temperatures above 1120K whereas that of CO₂ from C becomes lower above 1323K than Δ_fG⁰ of ZnO. However, Δ _fG⁰ of CO₂ from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn but not CO. therefore, out of C and CO, C is a better reducing agent than CO for ZnO.

The value of Δ _fG⁰ for the formation of Cr₂O₃ is – 540 kJ mol^-1 which are higher than that of Al₂O₃ is – 827 Kjmol^-1. Thus, Al can reduce Cr₂O₃ to Cr. Hence, the reduction of Cr₂O₃ with Al is possible.

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Freons or chlorofluorocarbons [CFCs] are aerosols that accelerate the depletion of ozone. In presence of ultraviolet radiation [UV radiation], these chlorofluorocarbons break down to give chlorine ions which combine with the ozone atoms in the atmosphere to give oxygen atoms.

The standard Gibbs free energy formation of ZnO from Zn is lower than that of CO₂ from CO. That is why CO cannot reduce ZnO to Zn. thus, Zn is not extracted from ZnO through reduction using CO.

For the group of low-grade copper ores, leaching is carried out using acid or bacteria in the presence of air or oxygen. In this process, copper goes into the solution as Cu²⁺ ions.

The resulting solution is then treated with scrap iron or H₂ to obtain metallic copper.

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Stability of an ionic compound depends on its lattice energy. More the lattice energy of a compound, more stable it will be. Lattice energy is directly proportional to the charge carried by an ion.

When a metal combines with oxygen, the lattice energy of the oxide involving O^2- ion is much more than the oxide involving O^- ion. Hence, the oxide having O^2-ions are more stable than oxides having O^-. Hence, we can say that formation of O^2- is energetically more favorable that formation of O^-.

Cryolite (Na₃AlF₆) has two roles in the metallurgy of aluminium:

(i) It lowers the melting point of the mixture to about

(ii) It increases the electrical conductivity of the

Copper matte contains Cu₂S and FeS. When a blast of hot air is passed through molten matte took in a silica lined convertor, FeS present in matte is oxidized to FeO which combines with Silica (SiO₂) to form FeSiO₃, slag.

When the whole of iron has been removed as slag, some of the Cu₂S undergoes oxidation to form Cu₂O which then reacts with more Cu₂O to form copper metal.