[yitzik]

I understand that the heat released when burning alcohols is greater as long as the number of carbons in the alcohol chain is increased (i.e the enthalpy of butanol is greater than propanol > ethanol> methanol). my question is about the rate of combustion. which of those alcohols will burn faster? is there any relation between the rate of combustion and the number of carbons in straight alcohols (or straight chain hydrocarbons)? I know that the evaporation rate is inversely proportional to the number of carbons in the chain, is there a different relationship regarding the rate of combustion?

this is actually my question, but i would like to share what brought me to ask this. we have made an experiment with a bomb calorimter to determine the enthalpy of combustion of the first 4 alcohols. i have made 4 plots of the temperature v.s. the time and calculated the temperature change and ultimatelty the enthalpy. yet it seems from the shape of the graph's that the increase in temperature is steeper for the long chain alcohols. i'm not sure if it's just my imagination or that there is really a significant relation here. is that actually indicating that as the number of carbons is increased- the rate of combustion is faster?

[Borek]

Define rate of combustion and propose how to measure it.

[yitzik]

RATE OF COMBUSTION:    the time it takes to 1 mole of alcohol to burn completly.
i measure the change in temperature (final-initial) during the burning of the alcohol in the calorimeter and devide it by the time it took to reach the final temperature.

thanks!

[yitzik]

although i must say that i actually used weight instead of moles, about 2 gram for each type of alcohol...

[Enthalpy]

The speed of a combustion depends on many things unrelated with the burned molecule. It could be the speed of evaporation, how finely the fuel is mixed with the oxidiser, how dilute the oxidiser is (oxygen or air), whether a shock wave can feed itself, and so on. So it's not a property of the fuel.

What is your setup in the calorimetric bomb? If the alcohol is liquid in a cup, then the evaporation rate might well determine the duration of the combustion. Injecting the fuel as a mist like a Diesel engine does would burn it much faster.

[Borek]

RATE OF COMBUSTION:    the time it takes to 1 mole of alcohol to burn completly.

How are you going to take into account all factors mentioned by Ehthalpy?

[billnotgatez]

From WIKI

Molar mass
n-butanol    74.123 g/mol
n-propanol  60.096 g/mol
ethanol       46.069 g/mol
methanol    32.04 g/mol