Posted by **kelsie** on Monday, October 13, 2008 at 7:48pm.

Enormous numbers of microwave photons are needed to warm macroscopic samples of matter. A portion of soup containing 177 g of water is heated in a microwave oven from 20degrees Celsius to 98 degrees Celsius, with readiation of wavelength 1.55x10^-2m. How many photons are absorbed by the water in the soup?

- chemistry -
**DrBob222**, Monday, October 13, 2008 at 8:12pm
Calculate q for the heat required to heat the soup.

q = mass x specific heat H2O x delta T.

q = ?? in Joules.

Then use E = hc/wavelength to determine the energy per photon. Go from there. Post your work if you get stuck. Check my thinking.

- chemistry -
**Sam**, Tuesday, November 25, 2008 at 8:30pm
ok. whew. just put in my answer into webassign and i got it correct.

Ill show the example with the numbers I was given. That way you can actually do the problem with your numbers.

I found the way to do this at the link below.

so my water mass was 360 g

my temp went from 28C to 93C

the radiation of wavelength is 1.55 x 10-2 m (same)

k so the first thing to do is find the work needed.

Q=mcΔT

this is mass times (4.184J/g°C) ΔT. so (360)(4.184)(93-28) = 97905.6 J. The 4.184 changes things to Angstroms. The overall equation will have the units Joules.

k so we also have the equations

E'=hv and c=λv

h = 6.626 x 10^-34

c = 3 x 10^8

solve and replace so that somehow you get this

Q (97905.6 J) / (hc/1.55 x 10^-2)

so 97905.6/((6.626e-34)(3e8)/(1.55e-2))

I got 7.6e27

webassign verified it.

- your mom -
**Anonymous**, Monday, February 7, 2011 at 2:48pm
its so easy

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