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The equation below shows the thermite reaction, which has often been used for welding iron.
8 Al (s) + 3 Fe3O4 (s) ----------> 4 Al2O3 (s) + 9 Fe(s)
ΔH = -3350*KJ/mol rxn
1. It is highly exothermic; the reacting mixture can reach temperatures as high as 3000°C. 8 Al(s) + 3 Fe3O4(s) ® 4 Al2O3(s) + 9 Fe(s) DH° = –3350 kJ How much heat would be released by the reaction of 47.6 g of Al with 69.12 g of Fe3O4?

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Answer:

335 Joules kJ of heat will be released

Explanation:

Given the balanced equation:

8 Al (s) + 3 Fe3O4 (s) ----------> 4 Al2O3 (s) + 9 Fe(s),

ΔH = -3350*KJ/mol rxn

This is the heat  released when 8 moles of Al react with 3 mol Fe3O4.

We then need to calculate the moles of reactants, verify if there is a limiting reagent and proceed to answer the question based on the soichiometry of the reaction.

Atomic weight Al = 26.98 g/mol  Molecular Weight Fe3O4 = 231.53 g/mol

mol Al = 47.6 g/26.98 g/mol = 1.76 mol

mol Fe3O4 = 69.12 g/ 231.53 g/mol = 0.30 mol

Limiting reagent calculation:

8 mol Al / 3 mol Fe3O4  x 0.30 mol Fe3O4 =  0.80  mol Al are required and we have 1.76 mol, therefore  Fe3O4 is the limiting reagent

Amount of Heat

-3350 kJ/ 3 mol Fe3O4  x 0.30 mol Fe3O4 = -335.00 kJ

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