Endothermic vs Exothermic

[EmilyC_3D]

Is the best way to tell if a reaction is endothermic vs exothermic, just the look at delta H or are there other factors we should be looking at in problems?

[Neel Sharma 3F]

If the delta H is provided then that is the easiest way to tell. However, if it is not provided you can sometimes use the knowledge on the relative stability of products to tell if heat will be required or released. Often when bonds form and the resulting molecule is more stable than the reactants, heat is released. When the product is less stable than the reactant, energy is inputted. Hope this helps!

[Sana Nagori 2H]

I think delta H is what we look at because it tells us whether the heat of the system increased or decreased with the reaction

[Hannah Lechtzin 1K]

The change in H (delta H) is the best way to tell. If delta H is greater than zero it is endothermic, while if it is less than zero it is exothermic.

[Christine Nguyen 3D]

Adding on to everyone else's responses, it would be an endothermic reaction if it requires heat, favoring the formation of the products. It would be exothermic if heat is released, favoring reactant formation. Another way of looking at it is reviewing the dimerization of nitrogen dioxide: 2 NO2(g)<-> N2O4(g). The forward reaction would be exothermic because you are taking 2 moles of NO2 and putting them together to form 1 mole of N2O4, thus, releasing heat. The reverse reaction would be endothermic because you are using (adding) energy to break 1 mole of N2O4 into 2 moles of NO2. Hope this helped!

[Yun Su Choi 3G]

As a rule of thumb, breaking a bond requires energy so it is endothermic. On the flip side, forming a bond releases energy, making it exothermic.

[sophia kosturos 2B]

If delta H is provided, that that is the easiest way to tell whether a reaction is exothermic or endothermic. If delta H is positive then the reaction is endothermic and if the delta H is negative then the reaction is exothermic. If the delta H is not provided then you must have to assume that if bonds are being broken then that requires energy and is thus endothermic. And on the flip side, if bonds are being formed then that releases energy and is exothermic.

[rhettfarmer-3H]

Yes, delta H is a perfect and most direct way to tell if it's endothermic or exothermic. endothermic being negative(absorbed) and exothermic positive(released). Another way to tell is where the heat is. If heat is in the product then it's exothermic and if it's a reactant it's endothermic.