molar heat of combustion question (1 Viewer)

[megaman64]

mass of water = 250g
initial mass of burner = 221.4g
final mass of burner = 219.1g
initial temp of water = 19 C
final temp of water = 59 C

ethanol was used in the burner

calculate the molar heat of combustion of ethanol, using the data

i got 209KJ/mol, but the answers say 838KJ/mol

and i dont know what i got wrong. can anybody help?

Thanks

 

[Parvee]

delta H1=mCdeltaT, where m is 0.25, C is 4.18x10^3 and delta T is 40
You should get delta H1=41800J
delta H2=-deltaH1, where delta H2 is the heat released by the fuel

Molar heat of combustion= delta H2/(mass/molar mass), where your mass is 2.3g (mass of ethanol used) and molar mass of ethanol is 46
You should end up with -836000J=-836kJ

 

[megaman64]

i did (2.3/46)x41800 i dont know why you need to divide it.

 

[Parvee]

That's the formula for molar heat of combustion.