Chemistry · The rate and extent of chemical change. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The rate of reaction tells you how fast a reactant is used up or a product is formed. To measure it you need a quantity that changes and the time it takes to change. You can measure the volume of gas collected in a gas syringe, the loss of mass as a gas escapes from a flask on a balance, or the time for a cross under the flask to disappear as the mixture goes cloudy.
On a graph of amount of product against time, the slope shows the rate. A steep line means a fast reaction. The curve becomes less steep as the reactants are used up and is flat when the reaction has stopped. The slope of a tangent gives the rate at one moment.
Students divide time by quantity, or leave the time in minutes when the answer is wanted per second. Put the quantity on top, the time underneath, and change minutes to seconds first.
Answer: 0.60 cm3/s
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