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प्रश्न
The reaction,
Cr2O3 + 2Al → Al2O3 + 2Cr
(ΔGθ = -421kJ) is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?
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उत्तर १
The change in Gibbs energy is related to the equilibrium constant, K as
`triangleG = -RTInK`
At room temperature, all reactants and products of the given reaction are in the solid state. As a result, equilibrium does not exist between the reactants and the products. Hence, the reaction does not take place at room temperature. However, at a higher temperature, chromium melts and the reaction takes place.
We also know that according to the equation
`triangleG = triangleH-TtriangleS`
Increasing the temperature increases the value of `TtriangleS` making the value of `triangleG` more and more negative. Therefore, the reaction becomes more and more feasible as the temperature is increased.
उत्तर २
This is explained on the basis of Keq, the equilibrium constant. In the given redox reaction, all reactants and products are solids at room temperature, so, there is no equilibrium between the reactants and products and hence the reactions does not occur at RT. At high temperature, Cr melts and values of TAS increases. As a result, the value of `triangle_rG^theta` becomes more negative and hence the reaction proceeds rapidlyt
संबंधित प्रश्न
How is ‘cast iron’ different from ‘pig iron’?
Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?
The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.
In the extraction of copper from its sulphide ore, the metal is formed by the reduction of \[\ce{Cu2O}\] with ______.
In the metallurgy of aluminium ______.
Choose the correct option of temperature at which carbon reduces \[\ce{FeO}\] to iron and produces \[\ce{CO}\].
For the reduction of \[\ce{FeO}\] at the temperature corresponding to point D, which of the following statements is correct?
For the metallurgical process of which of the ores calcined ore can be reduced by carbon?
(i) Haematite
(ii) Calamine
(iii) Iron pyrites
(iv) Sphalerite
The mixture of compounds A and B is passed through a column of \[\ce{Al2O3}\] by using alcohol as eluant. Compound A is eluted in preference to compound B. Which of the compounds A or B, is more readily adsorbed on the column?
Why is sulphide ore of copper heated in a furnace after mixing with silica?
Write down the reactions taking place in Blast furnace related to the metallurgy of iron in the temperature range 500-800 K.
Explain the following:
\[\ce{CO2}\] is a better reducing agent below 710 K whereas \[\ce{CO}\] is a better reducing agent above 710 K.
Explain the following:
Generally sulphide ores are converted into oxides before reduction.
Explain the following:
Carbon and hydrogen are not used as reducing agents at high temperatures.
Heating of MgCl2 6H2O in absence of HCl gives ______.
Carbon deposition reaction taking place in ______.
Assertion: For the extraction of iron, haematite ore is used.
Reason: Haematite is a carbonate ore of iron.
\[\ce{Au + CN^- + H2O + O2 -> [Au(CN)2]^- + OH^-}\]
The number of CN− ions involved in the balanced equation is ______.
