Question

Predict whether each of the following reactions would be spontaneous or non spontaneous under standard conditions or if it is impossible to tell with the data given.
a)2KClO3(s)+3C(s)-->3CO2(g)+2KCl(s) Exothermic

b) 2NO(g) + O2(g) ---> 2NO2(g) Exothermic

c)H2(g)+Zn(ClO3)2(s)-->2HClO3(l)+Zn(s) Endothermic


Does information come from the state the elements are in from reactant to product? I know that the exo/endothermic is useful but I do not remember how to use it.

Answer 1

Frankly, I think there is insufficient information for all of them. You need delta G. In a general sense exothermic reactions (delta H is -) often are spontaneous unless delta S screws things up and endothermic reactions (delta H is +) unless delta S screws things up. Technically, however, you need both delta H as well as T and delta S so you can calculate delta G from dG = dH - TdS.

Answer 2

In the problem it states if the reactions underwent standard conditions, would that mean they would all have the same temperature and delta s meaning the only thing that would ,make the difference is the delta H?

Answer 3

I think standard conditions in this case means 25 C and 1 atm and ALL will have those conditions. What counts is dH and dS where
dHrxn = (n*dHf products) = (n*dHf reactants) and
dSrxn = (n*dSf products) - (n*dSf reatants) or
dGrxn = (n*dGf products) - (n*dGf reactants)