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calculation of enthalpy change

in class i heated 500cm^3 of water using 3 an alcohol.
now i started with 104.61g of propan-1-ol and ended with 103.21, so the total mass of alcohol burnt is 1.40g. the intitial temp. of the water was 18oC and end temp. was 28oC, so a temp. change of 10K.
this is what i got so far-
energy change in water=mass X specific heat capacity X temp change
=500 X 4.18 X 10
=20900 J mol^-1
number of moles of propan-1-ol=1.4/60=0.02333mol
the question asks to calculate the energy when one mole of alcohol is burnt.
how do i do this...thanks.

Reply 1

Myth717

I got 23.4 :s-smilie:

but now im confused as I knw its wrong

Reply 2

devan5

propan-1-ol is C3H8OH=>Mr of 61

1.4/61=0.023 mol

so 0.023mol gives 20900jmol^-1
therefore 1mol=20900/0.023

1mol=908695.6522 J mol^-1

i think this is the right answer.

Reply 3

zafaru123

in my data book, enthalpies of combustion of one mole, the value is about 2000kJ for propan-1-ol

Reply 4

devan5

the final answer i gave was depending on this (in class i heated 500cm^3 of water using 3 an alcohol.
now i started with 104.61g of propan-1-ol and ended with 103.21, so the total mass of alcohol burnt is 1.40g. the intitial temp. of the water was 18oC and end temp. was 28oC, so a temp. change of 10K.) has the book taken this into consideration?