What is the energy of a photon that emits a light of frequency 7.21 x 1014 Hz? A. 4.78 x 10-19 J B. 2.76 x 10-19 C. 1.0910-19 J D. 4.16 x 10-19 J

E = 4.78×10^−19 J

Explanation:

The chemical equation for the energy of a photon is given by:

E =hν , where h is the Planck constant and ν is the frequency.

E =hν = 6.626×10^−34 Js × 7.21×10^ 14

s−1 = 4.78 × 10^−19 J

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explanation:

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"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"