Question:
The reaction $Cr_2O_3 + 2Al \to Al_2O_3 + 2Cr (\Delta G^? = - 421\, kj)$ is thermodynamically feasible due to -ve value of $\Delta G$. Why does this reaction not take place at room temperature?
The reaction $Cr_2O_3 + 2Al \to Al_2O_3 + 2Cr (\Delta G^? = - 421\, kj)$ is thermodynamically feasible due to -ve value of $\Delta G$. Why does this reaction not take place at room temperature?
Updated On: Jul 7, 2022
- Certain amount of activation energy is essential for thermodynamically feasible reactions also
- Due to high melting point of chromium oxide the reaction does not take place
- Overall value of $\Delta G$ for the net reaction becomes positive
- Molecules of $Cr_2O_3$ and $Al$ are not oriented properly
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The Correct Option is A
Solution and Explanation
The spontaneous reaction also requires a certain amount of activation energy therefore heating is required.
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Concepts Used:
Concentration of Ore
The concentration of ore, also known as ore enrichment, is the process of removing gangue particles from ore in order to enhance the percentage of metal in the ore. The difference in physical or chemical properties of the ore and the impurities determines the procedures used to remove impurities from the ores.
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- Hand-picking - It was the traditional system of directly concentrating ore with the hands. With the use of a hammer, the gangue or adhering solid matrix is removed from the ore in this procedure. The separation and identification of gangue are based on colour or lump form differences.
- Hydraulic Washing - On passing the ore via an upward stream of water, the lighter gangue particles are separated from the heavier metal ore. This is a gravity separation method.This process is used to enrich ores that are heavier than the gangue particles that are present in them. A stream of water is run through crushed and finely powdered ore in this procedure. Water washes away the lighter gangue particles, leaving the larger ore particles behind.
- Froth Floatation Process - The purpose of this process is to extract gangue from sulfide ores. The ore is pulverized and mixed with water to form a suspension. Collectors and Froth Stabilizers are added to this. Collectors like pine oils, fatty acids, etc. boost the metal part of the ore’s non-wettability, allowing it to form a froth.