Find the total number of collisions between molecules in 1.00 s in 1.00 l of nitrogen gas at standard temperature and pressure ( 0 °c , 1.00 atm). use 1.88 × 10−10 m as the effective radius of a nitrogen molecule. (the number of collisions per second is the reciprocal of the collision time.) keep in mind that each collision involves two molecules, so if one molecule collides once in a certain period of time, the collision of the molecule it hit cannot be counted.