According to the book I'm studying, the unit of permittivity is C^2/ N ∙ m^2. This unit can be expressed as farads per meter. How so?

The potential energy in a capacitor is 1/2 ∙ Q ∙ V = 1/2 ∙ C ∙ V^2 = Q^2 / (2 ∙ C). The units of this potential energy are Joules. Why are Joules the units for electrical potential energy?

Thanks!

Jagella