According to bond energy tables, the triple bond of N2 is 946 kJ/mol while the bond of I2 is 151 kJ/mol. Based on simple chemical ideas about what molecular properties lead to activation energies, it is reasonable to expect that the reaction of H with N2 will have a higher activation energy than the reaction of H with I2.
1. Yes, I2 is heavier than N2.
2. No, bond energies do not matter much; lone pairs are crucial.
3. Yes, in both cases the reactant bond must be stretched by collisions and more energy is required for the stronger bond.
4. Yes, in both cases the reactant bond must be broken before the H can bond.
5. No, activation energies have nothing to do with bond energies.

Let us remind ourselves of the basics of the collision theory. According to this theory, chemical reaction occurs because of the collision of particles of substances in a chemical reaction system.

This means that the bond between reactants must first be broken and new bonds formed in products. Activation energy is the minimum energy required for a reaction to occur. This energy goes into the rearrangement of reactant bonds to enable them to recombine and form products.

Since the N2 bond energy is far higher than the I2 bond energy, a greater degree of energy is needed overcome the energy barrier in the reaction of H2 with N2 compared to the reaction of H2 and I2 . Therefore, the activation energy for the reaction of H2 and N2 is much higher than the activation energy for the reaction of H2 with I2.