Homework 2 - solutions

# Homework 2- - #2solutions Due 1 , structure,adensityof22.4g/cm3,.2gmol1 ForFCC,n=4atoms/unitcell,andV = 16R 3 2.Now C nAIr = V N CA Andsolvingf

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MAT 33 – Fall 2008 Homework #2 - solutions Due: 08/09/08 1) Calculate the radius of an iridium atom, given that Ir has an FCC crystal structure, a density of 22.4g/cm 3 , and an atomic weight of 192.2 gmol -1 . For FCC, n = 4 atoms/unit cell, and V C = 16 R 3 2 . Now, ρ = nA Ir V C N A And solving for R from the above two expressions yields R = nA Ir 16 ρ N A 2 1/3 = 4 atoms/unit cell ( 29 192.2 g/mol ( 29 2 ( 29 16 ( 29 22.4 g/cm 3 ( 29 6.023 x 10 23 atoms/mol ( 29 1/3 = 1.36 x 10 -8 cm = 0.136 nm 2.) Many elements and compounds exist in more than one crystalline form under different conditions of temperature and pressure. This phenomenon is called polymorphism . Calculate the theoretical volume change accompanying a polymorphic transformation in a pure metal from the FCC to the BCC crystal structure. Assume the hard-sphere model and that there is no change in atomic volume before and after the transformation. For the FCC crystal structure unit cell, the atoms are in direct contact along the

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## This note was uploaded on 02/10/2009 for the course MAT 33 taught by Professor Keith during the Spring '07 term at Lehigh University .

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Homework 2- - #2solutions Due 1 , structure,adensityof22.4g/cm3,.2gmol1 ForFCC,n=4atoms/unitcell,andV = 16R 3 2.Now C nAIr = V N CA Andsolvingf

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