F10Q12W15 - CHEM 0110 QUIZ 12 WEEK 15 MONDAY, 1:00 PM...

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CHEM 0110 QUIZ 12 WEEK 15 MONDAY, 1:00 PM December 6, 2010 NAME_______________________________________________________________________ 1. The enthalpy of fusion (melting) of ice, H 2 O(s), is ΔH fusion = +6.01 kJ/mol. a) How much heat in J is needed to melt 2.85g of ice? b) Is fusion of ice exothermic or endothermic? c) In summer, we cool drinks, sometimes to 0 o C, by adding ice. Explain carefully how this cooling is brought about by the ice. 2. a) Draw Lewis structures for (i) CH 3 Cl and (ii) CO 2 b) Which intermolecular forces are shown by each of these species? ANSWERS 1. a) Heat = 2.85 g x kJ 1 J 1000 x mol 1 kJ 6.01 x g 18.0 mol 1 = 952 J b) Endothermic c) Some of the ice melts, drawing heat energy from the drink. As the ice melts at 0 o C, it is possible to cool the drink all the way to that temperature. 2. a) H C H Cl H O C O b) CH 3 Cl: London or dispersion force; dipole-dipole CO 2 : Dispersion force only For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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CHEM 0110 QUIZ 12 WEEK 15 MONDAY, 6:00 PM December 6, 2010 NAME_______________________________________________________________________ 1. The equilibrium vapor pressure of H 2 O ( ) at 38 ° C is 49.7 mm Hg. Calculate the mass of water in a room of volume 2.8 x 10 5 L, if the air is at 38 ° C and is saturated with water vapor. Assume ideal gas behavior. R = 0.0821 L atm/mol K; 1 atm = 760 mm Hg 2. a) Which has a higher boiling point, H 2 O or H 2 S? Give your reasoning. b) Is the hydrogen bond always stronger than London-dispersion forces or is it possible to find a species which has London forces which are stronger than the H-bond in, for instance, water? ANSWERS 1. p = 49.7 mm Hg x Hg mm 760 atm 1 = 0.0654 atm n = K 311 K x atm/mol L 0.0821 L 10 x 2.8 x atm 0654 . 0 RT pV 5 = = 717 mol Mass = 717 mol x 18.0 g/mol = 12.9 kg. 2. a) H 2 O. Experimentally we know that water is a liquid at room temperature, whereas H 2 S is a gas – its boiling point must therefore be below room temperature. In terms of intermolecular forces, water has hydrogen bonding, which is stronger than the dipole- dipole and dispersion forces in H 2 S. b) The strength of London forces increases with molar mass, and a species with a high molar mass, which is a solid at room temperature, has London forces which are stronger than the H bond in liquid water. An example would a very long-chain hydrocarbon. CHEM 0110 QUIZ 12 WEEK 15 TUESDAY, 8:00 AM For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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December 7, 2010 NAME_______________________________________________________________________ 1. a) Characterize each of the following species as molecular, metallic, ionic or covalent network.: KOH C 6 H 6 Cu HF b) Which, if any, of these species do you expect to be solids at room temperature? c) Give the name of each of these species.
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This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

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F10Q12W15 - CHEM 0110 QUIZ 12 WEEK 15 MONDAY, 1:00 PM...

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