MCQ
Tin is obtained from cassiterite by reduction with coke. Use the data given below to determine the minimum temperature (in $K$ ) at which the reduction of cassiterite by coke would take place.

At $ 298 K : \Delta_{ f } H ^{\circ}\left( SnO _2( s )\right)=-581.0 kJ mol ^{-1}, \Delta_{ fH } H ^{\circ}\left( CO _2( g )\right)=-394.0 kJ mol ^{-1}$

$S ^{\circ}\left( SnO _2( s )\right)=56.0 J K ^{-1} mol ^{-1}, S ^{\circ}( Sn ( s ))=52.0 J K ^{-1} mol ^{-1}$

$S ^{\circ}( C ( s ))=6.0 J K ^{-1} mol ^{-1}, S ^{\circ}\left( CO _2( g )\right)=210.0 J K ^{-1} mol ^{-1}$

Assume that the enthalpies and the entropies are temperature independent.

  • A
    $934$
  • $935$
  • C
    $936$
  • D
    $937$

Answer

Correct option: B.
$935$
b
$SnO _{2( s )}+ C _{( s )} \longrightarrow Sn _{( s )}+ CO _{2( g )}$

$\Delta H ^{\circ} r \times n =[-394]-[-581]=187 kJ / mole$

$\Delta S _{ rxH }^{\circ}=[52+210]-[56+6]$

$=200 J / k \text {-mole }$

$T =\frac{\Delta H ^{\circ}}{\Delta S ^{\circ}}=\frac{187 \times 1000}{200}=935 K$

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