what is the definiton of lucas reagent? what is the easiest way to define lucas reagents?

Lucas' reagent is a solution of zinc chloride in concentrated hydrochloric acid, used to classify alcohols of low molecular weight. The reaction is a substitution in which the chlorine replaces the hydroxyl group. Even though this reaction is normally very unfavorable, the zinc ion complexes with the hydroxyl group (by accepting a lone electron pair from O of -OH), making it a better leaving group. The remaining carbocation then combines with the chloride ion to form a chloroalkane.

Lucas' _test_ is a way of using Lucas' _reagent_ to figure out what kind of alcohol you have.  ("Kind" here just means is it a primary alcohol, or a secondary alcohol, or a tertiary alcohol.)

The rate at which the alcohol reacts with Lucas' reagent depends on the kind of alcohol.  Tertiary alcohols react very quickly.  Primary alcohols don't really react with the Lucas' reagent at all.  Secondary alcohols react, but slowly.

So if you add a few drops of Lucas' reagent to a test tube with your unknown alcohol, then you can look at the mixture in the test tube and see what kind of alcohol by what happens.  The mixture will turn cloudy, once it has reacted.  If it turns cloudy as soon as you add the reagent, then it must be a tertiary alcohol.  If it turns cloudy, but it takes a few minutes, it's probably a secondary alcohol.  If it never turns cloudy at all, it's probably a primary alcohol.