Why is it that a chemical with a lower enthalpy have stronger bonds?

[ninbam1k]

A chemical with a lower enthalpy has less energy in its bonds, making its bonds stronger and thus leaving it with greater stability.

Why is that? ^

Cheers.

[Graphite]

2 Ways to think about it. Just by looking at an energy profile: The energy of product must be lower than the energy of reactants to give a product-reactant enthalpy value below zero

2nd way: 1st law of thermodynamics - conservation of energy. If energy is released not as much is transferred to the new bond formation process

So it is stable because if it is lower in energy, means that the reaction is highly exothermic. Once the energy is released, it is unlikely that the products are able to capture this energy (activation) to undergo the reverse reaction

[ninbam1k]

i see, so, because a high amount of excess energy was released, the tendancy of reabsorbing the energy is quite low due to the extremely high energy being released, right?

cheers

[Graphite]

Yep, the energy is likely to diffuse away quickly and unlikely to be available.

[Mao]

In chemistry, we define zero enthalpy to be the energy of the system when every bond is broken (in the most over-simplified sense).

For a strong bond, we require a lot of energy to break this bond. I.e. we need to add a lot of energy to take it to zero enthalpy. Thus the enthalpy must be large and negative (lower).

For a weak bond, we require less energy to break the bond, thus the enthalpy is small and negative (higher).