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Sources of error in enthalpy change of combustion

Hello, the question asks which of these are sources of error in the experiment for determining the enthalpy change of combustion, resulting it becoming a less exothermic value.

1- some heat is lost to the surroundings
2-there may be some incomplete combustion
3-some fuel may evaporate duing the experiment

the options were, all of the above, only 1 & 2, only 2&3 or just 3

the answer is 3

i understand that some heat being lost to surroundings would make it less exothermic, because delta T is smaller, making Q smaller and delta H less exothermic.

But why does incomplete combustion or the fuel evaporating in the spirit burner effect it?

Thank you
Original post by ehlamleyla
Hello, the question asks which of these are sources of error in the experiment for determining the enthalpy change of combustion, resulting it becoming a less exothermic value.

1- some heat is lost to the surroundings
2-there may be some incomplete combustion
3-some fuel may evaporate duing the experiment

the options were, all of the above, only 1 & 2, only 2&3 or just 3

the answer is 3

i understand that some heat being lost to surroundings would make it less exothermic, because delta T is smaller, making Q smaller and delta H less exothermic.

But why does incomplete combustion or the fuel evaporating in the spirit burner effect it?

Thank you


Combustion is an example of an exothermic reaction. If the combustion reaction is incomplete, then the exothermic value will be less negative.
And how would you would that error from occurring?
Reply 3
Original post by ehlamleyla
Hello, the question asks which of these are sources of error in the experiment for determining the enthalpy change of combustion, resulting it becoming a less exothermic value.
1- some heat is lost to the surroundings
2-there may be some incomplete combustion
3-some fuel may evaporate duing the experiment
the options were, all of the above, only 1 & 2, only 2&3 or just 3
the answer is 3
i understand that some heat being lost to surroundings would make it less exothermic, because delta T is smaller, making Q smaller and delta H less exothermic.
But why does incomplete combustion or the fuel evaporating in the spirit burner effect it?
Thank you

If fuel evaporates, mass of alcohol used would be more than you actually used up. This would give more number of moles of alcohol used and make it less exothermic
(edited 4 weeks ago)

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