Watch the video of the thermite reaction, and then choose which of the following
ID: 837998 • Letter: W
Question
Watch the video of the thermite reaction, and then choose which of the following statements are correct for the thermite reaction. Check all that apply.
Check all that apply.
Check all that apply.
The internal energy of the system decreases
Calculate the standard enthalpy of the reaction, ?H?rxn, for the thermite reaction:
2Al(s)+Fe2O3(s)?2Fe(s)+Al2O3(s)
Elements in their standard state have an enthalpy of formation value of zero. The standard enthalpies of formation of Fe2O3 and Al2O3 are
?H?f of Fe2O3(s)=?825.5 kJ/mol
?H?f of Al2O3(s)=?1675 kJ/mol
Express your answer to three significant figures and include the appropriate units.
The internal energy of the reactants is more than the internal energy of the products. Heat is absorbed from the surroundings. The enthalpy change for the system is negative. The thermite reaction is endothermic.The internal energy of the system decreases
Calculate the standard enthalpy of the reaction, ?H?rxn, for the thermite reaction:
2Al(s)+Fe2O3(s)?2Fe(s)+Al2O3(s)
Elements in their standard state have an enthalpy of formation value of zero. The standard enthalpies of formation of Fe2O3 and Al2O3 are
?H?f of Fe2O3(s)=?825.5 kJ/mol
?H?f of Al2O3(s)=?1675 kJ/mol
Express your answer to three significant figures and include the appropriate units.
?H?rxn= value ?? units ??Explanation / Answer
The internal energy of the reactants is more than the internal energy of the products.
Consider ?Hreactant > ?Hproduct.
Then: ?Hreaction = ?Hproduct - ?Hreactant is less than zero because ?Hreactant is a larger number than ?Hproduct.
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The enthalpy change for the system is negative.
Consider the system the reaction. As I demonstrated above, the ?Hreaction is in fact negative. It's an exothermic reaction--you can tell from the video that it releases a lot of heat.
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The internal energy of the system decreases.
This is generally true because the products are lower in energy than the reactants. Thus the energy of the system tends toward a minimum.
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Calculations
As stated before, we have ?Hreaction = ?Hproduct - ?Hreactant
?Hreaction = ( 2?HAl2O3 + 1?HFe ) - ( 2?HAl + 1?HFe2O3 )
?Hreaction = (1(-1675 kJ/mol) + 2(0) kJ/mol) - (2(0) kJ/mol + 1(-825.5 kJ/mol))
Notice that when multiplying by the stoichiometric coefficients the number of moles cancels out.
?Hreaction = -849.5 kJ = -850 kJ (three sig figs)
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