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Higher Chemistry Enthalpy Calculation

Hey, does anyone know a simple step method on how to calculate the mass of an alcohol when in an enthalpy context. Can you please explain something simple and easy so that i can use it for similar questions please, thanks :smile:

3. Different fuels are used for different purposes.
(a) Ethanol, C2H5OH, can be used as a fuel in some camping stoves.
(i) The enthalpy of combustion of ethanol given in the data booklet is
−1367 kJ mol−1.
Using this value, calculate the mass of ethanol, in g, required to raise the
temperature of 500 g of water from 18 °C to 100 °C.
Show your working clearly
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Psraim
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Original post by Misshussain23
Hey, does anyone know a simple step method on how to calculate the mass of an alcohol when in an enthalpy context. Can you please explain something simple and easy so that i can use it for similar questions please, thanks :smile:

3. Different fuels are used for different purposes.
(a) Ethanol, C2H5OH, can be used as a fuel in some camping stoves.
(i) The enthalpy of combustion of ethanol given in the data booklet is
−1367 kJ mol−1.
Using this value, calculate the mass of ethanol, in g, required to raise the
temperature of 500 g of water from 18 °C to 100 °C.
Show your working clearly


Firstly, calculate heat evolved. Which is q=mcΔT, q=500*4.18*(100-18) = 171380J, this would be a negative value because it's combustion.
Convert it into kJ and substitute it into ΔH=q/mol, -1367 = -171.380/mol, rearranging this gives mol = -171.380/-1367, mol = 0.125...
Relative molecular mass of the alcohol in this context (Ethanol) is 46, multiply that with the value you got for moles to get the mass of the alcohol.
Mass of Ethanol required = 46*0.125... = 5.77g

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