SI Final Exam Practice Problems

SI Final Exam Practice Problems - ENGR 145 Chemistry of...

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ENGR 145 Chemistry of Materials Final Exam SI Practice Problems April 28, 2008 7:30 – 8:30 : Concept Review 8:30 – 10:30 : Practice Problems Schmitt Lecture Hall
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1. Molybdenum (Mo) is an important material that is commonly used in aircraft engines due to its ability to withstand very high temperatures without deformation or softening, and because it is Josh’s favorite element! Mo has an atomic number of 42, an atomic weight of 95.94 g/mol, and exists in a body- centered cubic crystal structure. a. Draw a schematic below of the crystal structure of Mo. Calculate the length of edge of the unit cell (also known as the lattice parameter) knowing that Mo has an atomic radius of 1.45 Å. b. Write the electron configuration for Mo. c. Draw the 4p, 5s, and 4d orbitals of the electron filling diagram for Mo. d. What type of magnetism will be present for Mo? Which type of magnetism will have a large enough effect to be measurable?
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e. Below is a list of crystallographic planes. Draw the each plane in the schematic unit cell. Determine whether or not the plane will meet the Bragg reflection condition and thus be present in an x-ray diffraction pattern for Mo (circle “YES” or “NO”). If the plane is present in the diffraction pattern, calculate the interplanar spacing, d hkl , and the angle at which the x-ray reflects off of the plane, θ , assuming n = 1 reflection. Plane: () 101 ( ) 311 () 031 Draw Plane Will reflection occur? YES NO YES NO YES NO Calculate d hkl (if applicable) Calculate θ (if applicable)
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2. Answer the following questions concerning impurities and material properties. a. Calculate the equilibrium number of vacancies per cubic meter for copper at 1000°C. The energy for vacancy formation is 0.9 eV per atom, and the atomic weight and density are 63.5 g / mol and 8.4 g / cm 3 , respectively. b. Describe the effect of impurities on thermal conductivity and explain why this behavior occurs. c. Describe the effect of impurities on carrier mobility in metals, and explain why this behavior occurs. If I were to increase the temperature of the sample in (a), how would the mobility change? d. Suppose to desire to construct a copper wire capable of carrying 5 Amps of current at room temperature. Wires need to have low resistance, so you do not want the resistance of the wire to exceed 1 Ω . You know the thermal conductivity of copper is 401 W / m K. What diameter should you wire be?
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3. Answer the following seemingly-random conceptual questions. a. Circle the term of phase that properly makes the following sentences about non-crystalline structures true . i. Ceramic glasses exhibit a large degree of ( long range order , short range order ) but have very little ( long range order , short range order ). ii.
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SI Final Exam Practice Problems - ENGR 145 Chemistry of...

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