Solve chemical reaction for temperature of exothermic reaction (thermite)

Question

Hi there, I I have a question about Physics/ chemistry.

If I have a bag of iron oxide(lll) and powdered aluminium in the ratio of 3:1 totalling 72g, with 54g being Fe2O3 and 18g of 2Al, what would the temperature be when it burns during the exothermic reaction? Can you give full working out and equations?

P.S the powder would be mixed and put in a plant pot.

Answer 1

First, just to set the record straight.  It should be iron(III) oxide, and no need for the 2 in front of Al, until you balance the equation.  So, the balanced equation would be:

Fe2O3 + Al ==> 2Fe + Al2O3

 

The temperature will be approximately 784ºC or about 1443ºF

 

To answer your question, you would first convert the mass of each reactant to moles, using the respective molar masses. Then calculate the moles of product formed based on the mole ratio of products to reactants.  Then calculate ∆H from 

∆H = Σ∆H products - Σ∆H reactants.  

 

Next use a similar procedure and calculate ∆S and ∆G of reaction.

 

Once you have ∆H, ∆S and ∆G, you can find the temperature from ∆G = ∆H - T∆S.

 

Or, you can simply look up the answer at http://chemistry-reference.com/reaction.asp?rxnnum=32