Hw 5J.11

[Amy Luu 2G]

Predict whether each of the following equilibria will shift toward products or reactants with a temperature increase:
a) N2O4(g) 2NO2(g), H°= +57 kJ
c) Ni(s) + 4CO(g) Ni(CO)4(g), H° -161 kJ

I am confused on how to determine whether the reaction is endothermic or exothermic. For a, since delta H is +57 kJ, I thought this meant that there is an increase in temperature of the environment and therefore must be an exothermic reaction since the reaction would be releasing heat/energy. I had the same thought process for c where I thought it was an endothermic reaction since there is a decrease in energy/heat so I assumed the reaction absorbed heat. Please clarify, thank you!

[vpena_1I]

It is the other way around. A positive delta H corresponds to an endothermic reaction in which the products formed have greater energy than the reactants. Energy can be thought of as a reactant in this case, which explains why an increase in heat will result in greater product formation.

[ELu 1J]

I think you just have to memorize that if delta H is negative, the reaction is exothermic and if delta H is positive, the reaction is endothermic.