Homework Help: Chemistry

Posted by Sarah on Monday, January 23, 2012 at 11:46pm.

A certain microwave oven delivers 633 watts (J/s) of power to a coffee cup containing 53.1 g of water at 25蚓. If the wavelength of microwaves in the oven is 9.75 cm, how long does it take, and how many photons must be absorbed, to make the water boil? The specific heat capacity of water is 4.18 J/蚓搽. Assume only the water absorbs the energy of the microwave.
___________ s
____________ photons

Chemistry - DrBob222, Tuesday, January 24, 2012 at 12:18am
How many J needed to raise T from 25C to 100 C? That is mass H2O x specific heat H2O x delta T = about 16,000 J but you need to get a more accurate number.

How much energy is available for a photon?
That is E = hc/wavelength =
6.626E-34*3E8/0.0975m = about 2E-24 J/photon.

2E-24 J/photon x # photons = 16,000
Solve for # photons.

633 J/s x # seconds = 16,000
Solve for # seconds.
Check my work. It's getting late.

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