Chemical Thermodynamics · JEE Main previous year questions

2010 2 questions

1. Q652010 · 25 Apr 2010 · Shift 1

   For a particular reversible reaction at temperature T, $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ were found to be both +ve. If ${\mathrm{T}}_{\mathrm{e}}$ is the temperature at equilibrium, the reaction would be spontaneous when :

   1. A.${\mathrm{T}}_{\mathrm{e}}>\mathrm{T}$
   2. B.$\mathrm{T}>{\mathrm{T}}_{\mathrm{e}}$
   3. C.${\mathrm{T}}_{\mathrm{e}}$ is 5 times $\mathrm{T}$
   4. D.$\mathrm{T}={\mathrm{T}}_{\mathrm{e}}$
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   Answer: B

2. Q752010 · 25 Apr 2010 · Shift 1

   The Gibbs energy for the decomposition of $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ at $500^{\circ }\mathrm{C}$ is as follows : $$\frac{2}{3}\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3\to \frac{4}{3}\mathrm{Al}+{\mathrm{O}}_2,{\Delta }_{r}G=+966\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$$ The potential difference needed for electrolytic reduction of $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ at $500^{\circ }\mathrm{C}$ is at least :

   1. A.4.5 V
   2. B.3.0 V
   3. C.2.5 V
   4. D.5.0 V
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   Answer: C