Explain the difference between the two quantities.
In a DC circuit the resistance of the componets you speak of are constant: the resistnce, R, will have a value of R Ohms; the capacitance, C, normally has a very high value, say, many Meg ohms; and the Inductor, L, is generally a lowish resistance. In AC circuits however, the resistance of both the capacitor and the inductor change depending on the frequency of the applied ac signal, while that of the resistor, R, still remains constant. It's because the resistance of the capacitor and inductor now depends upon the frequency of the signal that we give it a different name- we call it Reactance. We say that the capacitor has capacitive reactance and the inductor has inductive reactance; both of which are measured in ohms.
Impedance can have both resistive and either inductive or capacitive components (in electrical engineering-speak, we give the impedance as a complex number for a given frequency).
