destroyer chem 121

[arpitpatel86]

I have a big problem with these types of questions.......i keep getting confused when to do products minus reactants and when to do reactants minus products.....why do u not do products minus reactants on this problem....the that they divided each reach by 2......and how they cancel RHO out.....but they did reactants minus products...can some1 please clarify or maybe have an easiar method to know when to do products minus reactans or reactants minus products?


also tell me if im correct on this one: larger Ka= stronger acid
larger Kb= stronger base
smaller pKa= stronger acid?
smaller pkb= stonger base?

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[DRHOYA]

I don't have destroyer in front of me, so I can't answer your first question. However, you are correct in your pKa, Ka reasoning.

 

[arpitpatel86]

ne1?

 

[151AND8TH]

That's a Hess Law problem -- You divided by 2 because you are trying to get the coefficient of the product of step (b) which is 2RhO2 to be equal to the coeficient of the main reaction (product) which is RhO2.. and the same thing for the reactant of step (a) to that of the main reaction (reactant) which is Rh ----since you are in a "diving" everything by , you MUST alos divide the dH by 2. (-800/2)+(-300/2)=-550

again this is hess law.. I'd stay away from product minus reactant.. [reactant - product] is used when you are dealing with bond breaking/fromation. the rest of those state equations are [product-reactant]

The Hess trick is to remove anything that appears more than once then compare the coefficient of the steps to that of the main reaction