AP Chemistry
posted by qwerty123 .
Microwave ovens emit microwave radiation that is absorbed by water as heat. Suppose that the wavelength of the radiation that is 12.5 cm in an oven that has a power rating of 900 watts. (1W = 1 J/s)
a) How many moles of photons are released per minute
b) how long will it take to heat 100m.L of water from 20 Celsius to 100 Celsius. Assume all the water gets all of the microwaves energy as heat.

energy in J = hc/wavelength.That is E in J for 1 photon. Multiply by 6.022E23 to find moles. How many seconds will it take to at 900 watts. Multiply by 60 seconds/min.
Energy needed to heat water is
mass water x specific heat water x (TfinalTinitial) = q. 
A typical laser pointer is rated at 5.0 mW. It outputs red light with a wavelength of about 6300 Angstrom. How many photons of laser light will be emitted from the pointer if it is used 120 seconds.