And to supplement Mark's very splendid coverage of this question:
* Capacitive and Inductive Reactance are both 90° out of phase with DC resistance and are 180° out of phase with each other. As such, they are both the same except for whether the current leads or lags the voltage.
* In a pure resistance, the voltage and current are in phase with each other (i.e. a phase difference of 0). In a pure reactance, the voltage and current are 90° (or π/2 radians) out of phase with each other. The only difference between Inductive Reactance and Capacitive Reactance is the direction of that phase shift.
* The voltage across the Capacitive component of a circuit element lags the current by π/2. You can visualize this by doing the following thought experiment: When power is first applied to a fully drained capacitor, there is 0 volts across the capacitor and maximum current. As the capacitor charges, these conditions transition to the final state where the voltage across the capacitor is equal to the source voltage and the current flowing into ['through'] the capacitor is 0. ∴ voltage, which is at 0 at first, lags the current which is a full bore at the start of our experiment.
* The voltage across the Inductive component of a circuit element leads the current by π/2. A similar thought experiment illustrates this: when power is first applied to an inductor that has no energy stored in it, the full source voltage is across it and there is 0 current lowing through it until, finally, there is 0 voltage across the inductor and the maximum current is flowing (limited by any series resistance in the circuit).
* Capacitive Reactance is inversely proportional to the signal frequency (i.e. as the frequency [applied to the capacitor] goes up, the reactance goes down).
* Inductive Reactance is directly proportional to the signal frequency (i.e. as the frequency [applied to the inductor] goes up, the reactance also goes up).
* In a series or parallel capacitor/inductor circuit, the capacitive reactance and the inductive reactance will exactly cancel each other at the resonant frequency [leaving only the resistive component]. Another way of saying that: when the inductive reactance magnitude is equivalent to the capacitive reactance magnitude, in a circuit, they are at resonance. And, because the phase angle between the capacitive reactance and the inductive reactance is at opposition [180°], they exactly cancel when the magnitudes are the same.
* In DC resistance, because the current and voltage are in phase, there is power dissipation in the resistance [P=IE]. In pure AC Reactance, there is no power loss. Basically, the energy is stored and released but not dissipated. If any power dissipation occurs, it happened in some resistive component in the circuit. This can happen in a capacitor and in an inductor, since, in all but the most exotic cases [such as an inductor made out of superconducting material], these components are not pure capacitance or pure inductance. A capacitor, along with it's predominate capacitive character, also contains resistive elements and inductive elements -- in fact, at a high enough frequency (i.e. near at and above it's self resonant frequency) a capacitor behaves more like an inductor! And vice versa!!
