Integrated Concepts (a) An excimer laser used for vision...

Integrated Concepts (a) An excimer laser used for vision correction emits 193 -nm UV. Calculate the photon energy in eV. (b) These photons are used to evaporate corneal tissue, which is very similar to water in its properties. Calculate the amount of energy needed per molecule of water to make the phase change from liquid to gas. That is, divide the heat of vaporization in $\mathrm{kJ} / \mathrm{kg}$ by the number of water molecules in a kilogram. (c) Convert this to eV and compare to the photon energy. Discuss the implications.

Integrated Concepts
(a) An excimer laser used for vision correction emits 193 -nm UV. Calculate the photon energy in eV.
(b) These photons are used to evaporate corneal tissue, which is very similar to water in its properties. Calculate the amount of energy needed per molecule of water to make the phase change from liquid to gas. That is, divide the heat of vaporization in $\mathrm{kJ} / \mathrm{kg}$ by the number of water molecules in a kilogram.
(c) Convert this to eV and compare to the photon energy. Discuss the implications.

Key Concepts

Molecular Energy Calculation Using Avogadro’s Number

This concept involves scaling macroscopic thermodynamic quantities to the molecular level. By dividing a quantity such as the heat energy per kilogram by the number of molecules (which can be obtained using Avogadro’s constant), one can determine the energy required per individual molecule. This approach is fundamental in connecting bulk material properties to molecular-level interactions.

Energy Unit Conversion (Joules to Electron Volts)

Converting between energy units, particularly from joules to electron volts (eV), is a common practice in physics and chemistry. The electron volt is a convenient unit for expressing energies on a microscopic scale. This conversion allows for direct comparison of energies such as those of photons and molecular processes, thereby linking macroscopic thermodynamic phenomena with quantum mechanical events.

Ultraviolet Radiation

Ultraviolet (UV) radiation refers to electromagnetic radiation with wavelengths shorter than visible light, typically ranging from about 10 nm to 400 nm. UV light is particularly significant in contexts like photochemistry and medical applications, as its high photon energy (when using the appropriate wavelength) can produce effects such as breaking molecular bonds or inducing other chemical reactions.

Photon Energy Calculation

This concept involves the quantization of light energy, where a photon’s energy is determined using the equation E = hc/?. Here, h represents Planck’s constant, c is the speed of light, and ? is the wavelength of the photon. This formulation is critical in several fields such as optics and quantum mechanics, where understanding the energy level of specific wavelength photons, including those in the ultraviolet range, is essential.

Heat of Vaporization

The heat of vaporization is the amount of energy required to convert a substance from its liquid phase into a gas at a constant temperature. This thermodynamic concept is key in understanding phase transitions, as it quantifies the energy needed to overcome intermolecular forces holding molecules together in a liquid phase, an understanding essential in fields like physical chemistry and materials science.

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