Frequency of effective collisions

The frequency of effective collisions is the number of effective collisions that happen per unit time, and the rate of reaction depends directly on it. Malay: kekerapan perlanggaran berkesan · Chinese: 有效碰撞的频率.

This quantity is the bridge between the collision theory and every rate factor. An effective collision is one with enough energy and the correct orientation to react. If more of them happen each second, more product forms each second, so the rate is higher. Every way of speeding up a reaction works by raising this frequency, either by making collisions more frequent overall, or by making a larger fraction of them energetic enough to be effective, or both.

Example. Raising the concentration of a solution packs more particles into the same volume, so collisions, including effective ones, happen more often and the rate increases. Raising the temperature does two things at once: particles move faster, so they collide more often, and a greater fraction now has energy above the activation energy, so a much larger share of collisions is effective. Both routes increase the frequency of effective collisions.

Confusion to avoid. Do not write only about the total frequency of collisions. Concentration, surface area and pressure mainly change how often particles meet, but temperature and a catalyst change the fraction that is effective. A complete explanation states clearly that it is the frequency of effective collisions that rises, not just the number of collisions.

Because this single quantity controls the rate, it is the phrase examiners look for when you explain any factor, so anchoring your answers on the frequency of effective collisions makes them reliable in SPM Chemistry. Our teachers train students to end every rate explanation on this phrase so that no mark is lost to a loose ending.