79 kj to heat a cup of water?

It requires 79 kJ to heat a cup of water from room temperature to boiling in the microwave oven. If the wavelength of microwave radiation is 2.1×10−3m, how many moles of photons are required to heat the water?

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  • 1 month ago

    The energy of a single photon is

    hc/lambda

    where h = 6.626 x 10^(-34) J

    c = 3.00 x 10^8 m/s and

    lambda = 2.1 x 10^(-3) m.

    So the energy of 1 photon is around

    10^(-22) J but use a calculator.

    The energy of a mole of photons will then be

    around 60 J, and it will take around 1300 moles of photons to heat the water.

    But go back over this using a calculator.

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