Energy changes

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How do you calculate the standard enthalpy change of combustion for different alcohols if you are given the quantity of heat energy produced when 1.00 g of each alcohol was burned in a combustion calorimeter, e.g. 1.00 g of methanol produces 22.34 kJ of energy?

Igloo writes
 
Standard enthalpy changes are based on one mole of a substance as opposed to 1.00 gram. So the first thing you must do is to calculate the molar mass of the alcohol and then scale up the energy accordingly.
 
I shall use another example, rather than yours, so that you can see how the method works and then use it to carry out your calculations.
 
Assume you are told that 1.00 g of benzene, C₆H₆, releases 41.9 kJ of energy when completely burnt.
 
The first thing to do is to work out the molar mass of benzene:
M_r[C₆H₆] = (6x12) + (6x1) = 78 g mol^-1
 
So, if 78 g of benzene is completely burnt, the energy released would be 41.9 x 78 = 3270 kJ
 
Since energy is evolved in a combustion process, the reaction must be exothermic, so we must remember to include a negative sign in front of the answer.
 
The enthalpy change of combustion of benzene = - 3270 kJ mol^-1
 

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updated: 20 January 2006