What can cause the voltage across reactances in a series RLC circuit to be higher than the voltage applied to the entire circuit?
Why At series resonance the inductive and capacitive reactances are equal and cancel, so the circuit impedance drops to just the resistance and current reaches its maximum. That large current flows through XL and XC, producing voltages of Q times the applied voltage across each reactance. They are 180 degrees out of phase and cancel each other, so Kirchhoff's law still holds even though each individual reactive voltage can be many times the source voltage.
Watch out Low Q does the opposite: the voltage magnification factor is Q itself, so a high Q, not a low one, produces the big reactive voltages. Resistance limits the resonant current and therefore reduces the effect.
Series resonance = voltage magnification: V across L or C equals Q times the source voltage.