Calculation of rupture force in a covalent bond

A force is the derivative of a potential energy:

$$vec{F} = -vec{nabla} U$$

If you choose to apply a continuous force to stretch a bond until rupture, the force will need to exceed the restorative force (as described say by Hooke's law for small displacements from equilibrium) due to mutual attraction of the atoms. The maximum value of that restorative force is the maximum value of the gradient of the potential, therefore:

$$vec{F}_{text{rupture, continuous}} = (vec{nabla} U )_{text{max}}$$

Note a quadratic potential (such as leading to Hooke's law) does not predict rupture. You would require a more accurate description of the internuclear potential to compute the rupture force.