[potatopotato]

Hi

I want to know if this is done correctly for my lab (these are collected data and are calculated accordingly)...

3.   Ethanol combustion:
Mass of water = 175 ml x 1.00g/mL = 175g
Temperature change of water heated by ethanol burning
40ºC – 7ºC = 33ºC
The energy absorbed by water from ethanol burning
Q = m x c x Δt
Q = 175g x 4.2 J/gºC x 33ºC
Q = -24255 J or -24.255 kJ

4.   Ethanol combustion:
a.   Density of ethanol is 0.789 g/mL:   3.0 mL x 0.789 g/mL = 2.367g
The mass of ethanol consumed in combustion:   2.367g – 0g = 2.367g
b.   The combustion heat of ethanol =   -24255 J / 2.367g
    =   -10247 J/g
c.   The heat of combustion of ethanol to be C2H5OH:
= 2.367g / (2x12g/mol + 6x1 g/mol + 16g/mol)
= 2.367g / 46 g/mol
= 0.05 mol
            C2H5OH =   -24255 J / 0.05 mol
               =   -471368.8213 J/mol
               =   -471.37 kJ/mol

Is ethanol C2H5OH supposed to have less heat combustion than wax (paraffin) C24H50?? Or is it sources of error that can cause difference in answers... One of the questions asks me is "alcohol or wax the better fuel?"

Another question is is candle combustion complete or incomplete?

[enahs]

Your setup and calculations appear to be correct (I did not put them in a calculator and see if you just made a simple calculator mistake). You are however ~66% away from the accepted value....