Enthalpy of Fusion

[Lusin_Yengibaryan_3B]

How many photons with a wavelength of 713 nm are needed to melt 459 g of ice? How would we use enthalpy of fusion to go about solving this problem? What steps are required to answer this question? I don't believe it was discussed in lecture.

[Kayla Law 2D]

Hi! For this problem I started by converting the wavelength given in the problem to energy (remember to convert the nanometers to meters). So using E = (hc)/λ, you solve for the energy of the photon which is about 2.79 x 10^-19 J. Next, the enthalpy of fusion is given in the table that they linked in the question. Since the enthalpy of fusion is 333.6 J / g, and the question is telling you to calculate how many photons are needed to melt 459 g, you multiply (333.6 J / g) x 459 g to figure out how many joules are needed to melt 459 g of ice. (333.6 J / g) x 459 g = 153122.4 J. So, now you have how many joules are needed to melt 459 g of ice, and you have the joules per photon. The question asks how many photons are needed to melt 459 g of ice, so all that is left to do is 153122.4 J / 2.79 x 10^-19 J in order to get the number of photons needed. Using your values, I got 5.49 x 10^23 photons. I hope this helps! :)

[Ivan Huang Dis 3B]

I believe they give you a link within the problem that tells you the enthalpy of fusion use that as your threshold energy