A) ? 81.98 kJ
B) ? 819.8 kJ
C) ? 40.99 kJ
D) + 819.8 kJ
Correct Answer: B
Solution :
Given: Weight of iron burnt\[=4g;\] Heat liberated \[=29.28\,KJ\]and atomic weight of iron \[(Fe)=56\]. We know that in ferric oxide \[(F{{e}_{2}}{{O}_{3}}),\,2\,\,moles\]of iron or \[2\times 56=112\,gram\]of iron are burnt. We also know that when \[4grams\]of iron are burnt, then heat liberated = 29.28 kJ, therefore when \[112\,grams\]of the iron are burnt, then heat liberated \[=\frac{29.28\times 112}{4}=-819.8\,kJ\] (Minus sign due to liberation of heat).
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