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Thanks! So it's always trial and error? There's no way to work it out directly right?
View attachment 54313
Wouldn't A form H2O2 ?
And if not what will it form? like what would the equation be?
No, it would not be correct. The signs + and - are very important in Hess Law reactions, and it is important to keep them in mind while attempting questions of this sort.
but why? why wud that be not correct?
View attachment 54304
How to do this one?
I form the table but then I don't know what to do (which values for P and Q?)
help with this please
Iodine: Covalent and van der waals forces
oh.. I get your point but why not B?The answer is A.
From the diagram and the arrow showing the enthalpy change of formation, we can conclude that the bottommost layer is CO2(g).
Thus, the second from bottom level has to be Option C, which shows the elements in their standard states. Working our way upwards, we can see that the change from Option B to Option A is an enthalpy change of vaporisation, which is positive. Therefore, A is the top level.
yea right, but I'm talking about ENTHALPY CHANGE OF COMBUSTION of H2For enthalpy change of formation, the arrow must point from the individual constituents to the final product. If the arrow is in the opposite direction, the enthalpy change will have the same magnitude but opposite direction.
oh.. I get your point but why not B?
yea right, but I'm talking about ENTHALPY CHANGE OF COMBUSTION of H2
But don't all molecules have van der waals forces?Iodine: Covalent and van der waals forces
Silicon dioxide: Giant covalent
Sodium chloride: Ionic
Zinc: Metallic
Oh.. so it shud have been +2* enthalpy change of combustion? am I right?That's exactly the same. Recall the definition of combustion and you should realise that the arrow should be pointing toward the product of combustion.
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