What 2 factors determine whether a collision between reactants is effective

The kinetic energy and the orientation of the molecules.

Explanation:

As per the collision theory, in order for the reactants yield the products, the molecules or particles must collide with a kinetic energy greater than or equal to the activation energy, and they must collide in the right orientation for the old bonds can be broken and the new ones formed.

The particles of reactants that collide either with less kinetic energy than the needed or in a different orientation will not drive to formation of new products but will "bounce" without producing any chemical change.

This theory is in agreement with the observations that increasing the concentration of reactants increases the rate of reaction, because more collisions will be occur, such as increasing the temperature also increases the rate of reaction, because the collisions will be more energetic.