Imagine that the reactant mixture (substrate and reagents) is represented by a large number of people occupying a stadium or auditorium. There are two exit sites, one leading to location 1 and the other to location 2. The first exit site has eighteen turnstiles, each permitting passage of one person at a time, and only in one direction. The second exit has only two turnstiles. Consequently, the rate at which people can leave through the first exit is nine times greater than through exit 2. We may consider the people ending up in location 1 as equivalent to molecules of propyl alcohol, and those in location 2 equivalent to propene molecules.