Question

Both n-octane and isooctane have essentially the same heat of combustion. How is that possible if they have different structures? Explain.

Answer 1

we know that

n-octane and isoocatne are isomers

also

chemical formula of

n-octane ---> C8H18

iso octane --> C8H18

so

they bothe have the molecular formula

now

the combustion reaction for both of them is essentially the same

C8H18 + 12.5 02 ---> 8 C02 + 9 H20

So

finally

we can see that n-octane and iso-octane have different chemical structures

but they have the same number and types of bonds that are broken upon combustion

also

C02 and H20 are the products in both cases

we know that

heat of combustion depends on the bonds broken and bonds formed

here

bonds formed and bonds broken are same for combustion of iso octane and n-ocatne

as a result

both of them have the same heat of combustion