# Enthalpy change question help!!

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#1
I'm really stuck on this question to do with enthalpy change.

The standard enthral you of combustion of octane (c8h18) is -5512kjmol-1. Some octane was burnt in a calorimeter contains 300g of water. The temperature of the water went up by 55k. Calculare an estimated mass of octane
burnt.
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5 years ago
#2
(Original post by Jinneybean)
I'm really stuck on this question to do with enthalpy change.

The standard enthral you of combustion of octane (c8h18) is -5512kjmol-1. Some octane was burnt in a calorimeter contains 300g of water. The temperature of the water went up by 55k. Calculare an estimated mass of propane burnt.
Did you mean to work out the mass of octane? because if so I have done that. I'm also guessing you mean 55 degrees and not 55k.

You have to work out the energy using Q = mcΔT so 300 x 4.18 x 55 = 68.97 in kJ

Then you use the equation mol = Q/ΔH which is 0.0125 moles

To work out mass use g = n x M which works out to be 1.43g
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#3
(Original post by lucyjane_x)
Did you mean to work out the mass of octane? because if so I have done that. I'm also guessing you mean 55 degrees and not 55k.

You have to work out the energy using Q = mcΔT so 300 x 4.18 x 55 = 68.97 in kJ

Then you use the equation mol = Q/ΔH which is 0.0125 moles

To work out mass use g = n x M which works out to be 1.43g
Thanks I meant octane
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