Basically, resistance is something that obstructs the flow of charge because of collision of electrons flowing in the conducting wires on either side of the resistor with the ions in the resistor right? So say I have a 9V battery connected to a 100 ohm resistor, the potential drop across it would be the full 9V i.e. 9J of work is done per coulomb of charge.
However, when another resistor is connected in series, say another 100 ohm resistor, the potential drop across the first would (in this case) be halved. How is it possible for less amount of work to be done per unit charge? After all, there is no change in resistance or resistivity of the resistor right?
Have I simply got the definition wrong?