Units
From the expression for a discharging capacitor: Q(t) = Qoe-t/RC , we see that the quantity RC must have units of time. Let’s check it out:
From Ohms law: V=IR, Ohm=W= Volt/Amp;
By definition: C = Q/V, Farad = Coul/Volt.
units of RC: W*Farads = [Volt/Amp]*(Coul/Volt) = Coul/Amp = Coul/[Coul/sec] = sec.