Reactions happen at different rates

Chemical reactions take place at a variety of rates, for instance explosions are very rapid whereas iron rusts relatively slowly. Many ionic reactions in solutions happen in a fraction of a second and so they appear to be instantaneous . 

Most reactions that you will study happen in a matter of minutes some of these will be used as examples to show how the rate of a reaction might be quantitatively measured. 

In Unit 5.3 the ways in which reactions can be made to proceed more or less rapidly are discussed. 

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