Help with wavelength and frequency please?

Question

-What is the magnitude of the energy change associated with emission of one mole of photons of light with wavelength of 5.755×1014 Hz


- If it takes 2.0E-1 sec. for one wavelength of a wave to pass a stationary point, what is the frequency of the wave (Hz)


-What is wavelength of an electromagnetic wave the velocity of which is 3.0E+10 cm/sec and the frequency of which is 1.3E+17 Hz? (in cm)


-How much energy (in joules) is contained in one mole of photons (electromagnetic quanta) of frequency 9.0E+17 Hz?


PLEEEEEEEASE help
i have a test tomorrow and i need to know how to work these out
:)

Answer 1

One mole always consists of the same number of molecules, whatever the material, so I assume it contains the same number of photons:

http://en.wikipedia.org/wiki/Mole_(unit)

A single photon carries the energy determined by its frequency and Planck's constant:

E = h f
where h = Planck's constant and f = frequency in Hz

http://en.wikipedia.org/wiki/Planck's_constant

So given the number of photons and the energy for each, you can solve the first and last of your problems.

Regarding the second. If one wave follows another, and it takes P/Q seconds for each to pass, how many pass in one second?

Regarding the third, the general rule is:

wave length = velocity / frequency

see: http://en.wikipedia.org/wiki/Wavelength