In a past paper I did it said " C2H6 --->C2H5Cl" and the reagent was chlorine gas , but why doesn't chloroethane have two chlorines since there were two molecules of chlorine (Cl2)
In a past paper I did it said " C2H6 --->C2H5Cl" and the reagent was chlorine gas , but why doesn't chloroethane have two chlorines since there were two molecules of chlorine (Cl2)
There are two sources of confuzzlement...
There are not "two molecules of chlorine", rather there are two atoms in a molecule of chlorine.
I suspect you're getting radical substitution and electrophilic addition confused. Ethane (in your Q) is saturated, it won't do addition reactions.