Multiple choiceQuestion 1 · Recall
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By the end, you can define reaction rate and distinguish collision frequency, effective collisions and non-effective collisions.
Imagine reactant particles trying to get through a doorway. The rate of reaction tells us how quickly reactants disappear or products appear.
A fast reaction changes noticeably in a short time. A slow reaction changes only a little in the same time.
Rate of reaction
The rate of reaction is the change in concentration of a reactant or product per unit time.
For a reactant, its concentration decreases, so we usually use the magnitude of the change:
A common unit is .
Collision frequency
Collision frequency is the number of collisions between reacting particles per unit time.
More collisions per second do not automatically mean a faster reaction: the collisions must also be effective.
A collision is effective if it leads to a reaction. At this level, that means the particles collide with enough energy and the correct orientation for bonds to break and new bonds to form.
A non-effective collision is a collision that does not produce products. The particles may bounce apart because they lack enough energy, have the wrong orientation, or both.