Chemical a and chemical b react in an exothermic reaction. what can be known about what will happen when chemical a and chemical b are mixed together?

More energy will be released from the old substance than the new substance will need to form it's chemical bonds.

Explanation:

Given

Chemical A and Chemical B react in an exothermic reaction.

This means energy is released when they react to give products. The product formation also requires energy, which is got from the energy released when A and B reacts. The energy that is left after the formation of products is released as heat. So in order for a reaction to be exothermic, the energy released  by the reactants should be more than the energy required for the new chemical bonds to be formed to give the products.

1.43 x 10^-11 j the guy commented the awnser just making sure u see it .

a electronegativity decreases beacuse the size of nucleus is bigger.