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GCSE Chemistry · key term
A horizontal part of a graph where the measured quantity is no longer changing.
Used by Edexcel and OCR
Paper 1
A flat section of a temperature–time graph where the temperature stays constant.
Revise: Mathematical ApplicationsDuring the first plateau, the substance melts: energy is still being supplied, but its temperature stays constant while it changes state. The next rising section shows the liquid warming; the second plateau represents boiling. The graph therefore connects numerical readings with the physical changes you have studied.
Specification CM5.2ii, CM6.1ii · Paper 2 (Foundation), Paper 4 (Higher)
A plateau means the measured quantity has stopped changing. Do not automatically call it equilibrium: in a typical rate experiment, the limiting reactant may have been used up.
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The curve commonly becomes less steep as the reaction proceeds because reactants are being used up. It eventually reaches a plateau when the measured quantity no longer changes. In a typical experiment this may be because the limiting reactant has been used up; a plateau does not, by itself, prove that the system is at equilibrium.
A horizontal part of a graph showing that the measured quantity is no longer changing.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A level section of a graph where the measured quantity is no longer changing.
Revise: Drawing rate graphsThe horizontal section is a plateau: the measured volume is no longer increasing, so the rate of gas production is zero at that stage. In this example, about 45 cm³ is the total volume collected, not a rate.