what is difference between impedence and reactance?

Circuits with capacitors and inductors are more complicated than the resistive circuits we talked about earlier, in that their behavior depends on the frequency: A “voltage divider ” containing a capacitor or inductor will have a frequency dependent division ratio.
In addition, circuits containing these components (known collectively as reactive components), “corrupt” input waveforms such as square waves, as we just saw.
However, both capacitors and inductors are linear devices, meaning that the amplitude of the output waveform, whatever its shape, increases exactly in proportion to the input waveform’s amplitude. This linearity has many consequences, the most important of which is probably the following:
The output of a linear circuit, driven with a sine wave at the same frequency (with, at most, changed amplitude and phase).