Year 12s: what will be the first way you research your future options? >>

Enthalpy of Combustion from mean bond enthalpies

Scroll to see replies

Using multiples of the moles of molecules will affect the final answer because enthalpies of combustion are calculated for 'one mole' of a molecule. You have to divide your final answer by 2 to get the correct value (if you multiply the eqn by 2)... Also because you are using mean bond enthalpies rather than bond dissociation enthalpies most quotes will vary. As long as you use values from the same source you should get the right answer :smile:

Reply 21

kickass112

We were bieng taught Hess's Law today and at the moment I am sturggling to graps the logic behind it. In the examples we were given in class, we could have used Hess's law to find the enthalpy of combusting the reactant in air, etc. but because we were given all the necessary bond enthalpies, could have worked out overall enthalpy change straight from the reactant and product enthalpies

:?