The method used to measure the rate of reaction largely depends on the chemistry being investigated.

Typically we aim to measure the appearance of a product or the disappearance of a reactant over time.

If products are gaseous we can measure volume of gas produced or if the reaction is carried out in an open system then mass loss can be measured. Where evolution of a precipitate occurs then turbidity may be measured.

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The image above shows the equipment used to measure the rate of reaction between sodium thiosulfate and hydrochloric acid (a stop clock is also necessary). In the activity students measure the diappearance of the black cross on the paper as the sulfur precipitate obscures a view of the cross. This is a very common practical as it requires relatively simple equipment. However the level of equipment available in the laboratory may be a restricting factor and students may need to be enouraged to see a variety of methods in order to choose the one that best suits their needs based on accuracy and reliability.