A plateau is the flat part of a rate curve where the gradient is zero, showing that the reaction has stopped and no more product forms.
A plateau is the flat part of a rate curve where the gradient is zero, showing that the reaction has stopped and no more product is forming. Malay: plato · Chinese: 平台.
On a graph of gas volume or product mass against time, the curve rises steeply at first and then bends over until it becomes horizontal. This horizontal section is the plateau. A zero gradient means the measured quantity is no longer changing, so the reaction has finished. The reaction stops because one of the reactants, the limiting reactant, has been completely used up; any other reactant left over is in excess and cannot react further on its own.
Example. When a fixed mass of marble chips reacts with excess acid, the volume of carbon dioxide climbs and then levels off at a plateau. The height of that plateau is set by the amount of marble, the limiting reactant. If you repeat the experiment with more concentrated acid but the same marble, the curve rises more steeply and reaches the plateau sooner, but the plateau is at the same height, because the total amount of gas depends only on the limiting reactant, not on the rate.
Confusion to avoid. Do not read a higher plateau as a faster reaction. The steepness of the curve shows the rate; the height of the plateau shows the total amount of product. A faster reaction reaches the plateau sooner, but only more limiting reactant makes the plateau higher.
The plateau links the rate curve to the idea of a limiting reactant, and reading both the steepness and the final height correctly is a skill SPM Chemistry tests when it compares two experiments on one graph.
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