In a calorimeter, a 1g sample of aluminium oxide is formed. , 17kj of energy is released. The molar enthalpy of combustion of aluminium is?
2016-02-25 4:02 pm
I was having trouble with this. I got the answer thats a little too high. Some one help out and show how to do it. Thank you
回答 (1)
2016-02-25 4:19 pm
The molar enthalpy of combustion of aluminium means the enthalpy change when 1 mole of aluminium undergoes completely combustion in standard state.
Al(s) + (3/4)O₂(g) → (1/2)Al₂O₃ .... ΔH = ? kJ/mol
1 mole of Al gives 1/2 mole of Al₂O₃.
2 moles of Al gives 1 mole of Al₂O₃.
Energy released = 17 kJ
Molar mass of Al₂O₃ = 27×2 + 16×3 = 102
No. of moles of Al₂O₃ = 1/102 mol
No. of moles of Al used = (1/102) × 2 = 0.0196 mol
Molar enthalpy of combustion of Al = -17/0.0196 = -867 kJ/mol
Al(s) + (3/4)O₂(g) → (1/2)Al₂O₃ .... ΔH = ? kJ/mol
1 mole of Al gives 1/2 mole of Al₂O₃.
2 moles of Al gives 1 mole of Al₂O₃.
Energy released = 17 kJ
Molar mass of Al₂O₃ = 27×2 + 16×3 = 102
No. of moles of Al₂O₃ = 1/102 mol
No. of moles of Al used = (1/102) × 2 = 0.0196 mol
Molar enthalpy of combustion of Al = -17/0.0196 = -867 kJ/mol
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