Question

PLZ HELP!!!!!!!
how do you know if a reaction is going to completion??????????

Answer 1

That depends on what kind of reaction you are performing.
For example, a reaction that liberate gases (e.g. dil.HCl + Na -> H2) is completed when no more gas forms. For reaction that involves changing in colour of ions, like reduction of MnO4- to Mn2+, as the colour intensity is directly proportional to the conc. of MnO4- ion; when there is no more change in colour intensity (no more purple colour in this example), then you know there is no more MnO4-, i.e. reaction is completed. For reversible reactions, you can check the conc. of any reactant/product at regular intervals, say 5 mins. The reaction is at eqm (dunno if thats what u call complete tho lol) when there is no further change in conc. of any reactant/product. hope this helps :)