Question

i will medal and fan
What must be true of the bonds for a reaction to be endothermic, and
what must be true for the reaction to be exothermic.

Answer 1

Any time that a bond is formed, energy is released. Likewise, any time that a bond is broken, energy must be supplied. In an endothermic reaction, the energy required to break the bonds in the reactants must be greater than the energy released forming the bonds in the product. For an exothermic reaction, the opposite will be true: More energy is released in forming the bonds of the product than is absorbed to break the bonds in the reactants.

Answer 2

In an Endothermic reaction, you need to put in a certain amount energy to get the reaction going. On a reaction diagram for an endothermic reaction the energies of the products will be more than the reactants.

An exothermic reaction is defined by a release of heat which to my opinion would signify that the products are at a lower energy than the reactants, and hence more stable. Lower energy means more stable.

Don't forget that you need to put in energy regardless of whether the reaction is endothermic or ectothermic and that's called the activation energy the minimum energy you need to get the reaction to happen, because one requirement is that the particles have to be In the proper orientation/ have sufficient kinetic energy, in order to react.

Remember you need to put in energy to break bonds altogether, and that's how I understand activation energy.

Also when you form bonds you release energy.