Chemical Thermodynamics Question 474

Question: The standard heat of combustion of Al is $ -,837.8,kJ,mo{{l}^{-1}} $ at $ 25^{o}C $ . If Al reacts with $ O_2 $ at $ 25^{o}C, $ which of the following releases 250 kcal of heat-

Options:

A) The reaction of 0.624 mole of Al

B) The formation of 0.624 mole of $ Al_2O_3 $

C) The reaction of 0.312 mole of Al

D) The formation of 0.150 mole of $ Al_2O_3 $

Show Answer

Answer:

Correct Answer: B

Solution:

  • $ 2,Al+\frac{3}{2}O_2\xrightarrow{{}}Al_2O_3; $

$ \Delta H^{o}=-,837.8,kJ,mo{{l}^{-1}} $

2 mol 1.5 mol 1 mol 1 mol 0.75 mol 0.5 mol $ 837.8,kJ,mo{{l}^{-1}}\equiv $ Combustion of 1 mole Al or formation of 0.5 mole $ Al_2O_3 $

$ 250,kcal=\frac{250\times 8.314}{2},kJ $

$ =1.24,mol,Al $

or $ =0.62,mol $ of $ Al_2O_3 $



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