One of the difficulties experienced by students is the determination of rate by drawing a tangent to the curve and using gradient to determine rate. In many pre-16 and post-16 chemistry courses students are expected to be able to do this for both initial rate as well as rate at specific times during the reaction. This includes drawing tangents to the line and determining the rate at set times during a reaction.

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It may be worth discussing this with maths colleagues to find out when and where this is done in maths lessons so that you can be consistent with the language you use.