chemistry
posted by jordy .
What energy is required to excite a hydrogen atom in its n = 2 state to the n = 3 state ?

Isn't this the point of the Rydberg equation?
1/lambda= R(1/n^2 1/m^2)
but E=plancksConstant*c/lambda
so E=plancksconstant*c * R (1/n^21/m^2)
c is the speed of light, R is the Rydberg constant, m,m are the two states.
What is neat about this method is it can be 'extended' to other atoms, by the multiplication Z^2 where Z is the atomic number.