spring 08 midterm+2+practice

spring 08 midterm+2+practice - McKeachie Chem 1B spring 08...

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McKeachie Chem 1B spring 08 - Practice problems for midterm 2 1. What mass of water, in g, at 0 °C could be converted to ice at 0 °C simply from the vaporization of 26.0 g of liquid ammonia? ( H vap for NH 3 = 80.3 J mol -1 , H sub for H 2 O = 46.70 kJ mol -1 , H vap for H 2 O = 6020 J mol -1 ) 2. Of the following pairs, which would you expect to have the higher vapor pressure? the higher H fus ? Explain. a) Br 2 (s) vs I 2 (s) b) CaCl 2 (s) or Cl 2 (s) c) C 6 H 6 (l) or C 6 H 5 OH(l) d) CH 3 (CH 2 ) 4 CH 3 (l) or CH 3 (CH 2 ) 5 CH 3 (l) 3. One form of elemental tungsten crystallizes with a body-centered cubic unit cell. If incoming x-ray radiation with a wavelength of 0.204 nm is scattered in phase by the crystal at a 40 degree angle, what is the atomic radius of tungsten, in pm? 4. When an electron in excited molybdenum falls from the L to the K orbital shell, an x-ray is emitted. These x-rays are diffracted at an angle of 7.75° by planes in a solid with a unit cell separation of 0.264 nm. What is the energy difference, in J, between the L and K shells in atomic molybdenum? (Hint: In Chem 1A you probably learned that as electrons fall between energy levels in an atom, they must emit photons with very specific energies!) 5. Determine the empirical formula and oxidation state of each ion for the following cubic unit cells: a) A unit cell containing I ions at the corners and a cesium ion in the center. b) A unit cell containing rhenium ions at the corners and oxide ions at the center of each edge. c) A unit cell containing oxide ions in the center of each face, a titanium ion in the center of the cell, and calcium ions at the corners. 6. Automotive air bags inflate when a sample of solid sodium azide (NaN 3 ) rapidly decomposes into sodium metal and nitrogen gas. The airbag is inflated by the nitrogen. If 300.0 g of sodium azide are allowed to decompose completely at STP, what volume, in L, of nitrogen gas will be produced?
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